HFIP-mediated Desulfinative Friedel-Crafts Cyclobutenylation Reaction

In 1,1,1,3,3,3-hexafluoroisopropyl alcohol (HFIP), gem-bis(triflyl)cyclobutenes, which can be prepared by the (2+2) cycloaddition reaction of Tf2C=CH2 with alkynes, underwent desulfination to generate the corresponding cyclobutenyl cation. This unique reactivity was successfully applied to the Friedel-Crafts type cyclobutenylation reaction of several (hetero)aromatic compounds.

SN2 Reaction at the Amide Nitrogen Center Enables Hydrazide Synthesis

Nucleophilic substitutions are fundamentally important transformations in synthetic organic chemistry. Despite the substantial advances in bimolecular nucleophilic substitutions (SN2) at saturated carbon centers, analogous SN2 reaction at the amide nitrogen atom remains extremely limited. Here we report an SN2 substitution method at the amide nitrogen atom with amine nucleophiles for nitrogen-nitrogen (N-N) bond formation that leads to a novel strategy toward biologically and medicinally important hydrazide derivatives. We found the use of sulfonate-leaving groups at the amide nitrogen atom played a pivotal role in the reaction. This new N-N coupling reaction allows the use of O-tosyl hydroxamates as electrophiles and readily available amines, including acyclic aliphatic amines and saturated N-heterocycles as nucleophiles. The reaction features mild conditions, broad substrate scope (>80 examples), excellent functional group tolerability, and scalability. The method is applicable to late-stage modification of various approved drug molecules, thus enabling complex hydrazide scaffold synthesis.

Transition-Metal-Free Synthesis of 2-Substituted Benzo[cd]Indoles via the Reaction of 1-Halo-8-lithionaphthalenes with Nitriles

A simple and effective organolithium approach to the synthesis of 2-substituted benzo[cd]indoles from peri-dihalonaphthalenes and nitriles has been developed. The reaction proceeds via a surprisingly easy intramolecular aromatic nucleophilic substitution facilitated by the "clothespin effect". The discovered transformation provides good isolated yields, allows usage of an extensive range of nitriles, and demonstrates a good substituents tolerance. UV-absorption and NMR spectra of the obtained benzo[cd]indoles and their protonated forms demonstrated exclusive protonation to the indole nitrogen atom even in the presence of two NMe2 groups in positions 5 and 6 (i. e. "proton sponge" moiety).

One-Flow Synthesis of Substituted Indoles via Sequential 1,2-Addition/Nucleophilic Substitution of Indolyl-3-Carbaldehydes

Substituted indoles are important as drugs. A number of valuable indoles have been synthesized via nucleophilic substitution at the 3'-position of indoles. However, the preparation of an indolylmethyl electrophile containing a tertiary carbon at the 3'-position and its subsequent nucleophilic substitution are challenging owing to the instability of the electrophile. Herein, we demonstrated the rapid one-flow synthesis of indoles via sequential 1,2-addition/nucleophilic substitution of indolyl-3-carbaldehydes. The use of a microflow technology helped in suppressing the undesired reactions caused by the unstable intermediates, resulting in significantly higher yields and reproducibility compared to those under batch conditions. A crown ether was effective when 1-alkylindole-3-carboxaldehyde was used as a substrate. However, the crown ether exerted a detrimental effect when 1H-indole-3-carboxaldehyde was used. A total of 15 structurally diverse indole derivatives were obtained in generally acceptable to good yields.

A New Stereoselective Approach to the Substitution of Allyl Hydroxy Group in para-Mentha-1,2-diol in the Search for New Antiparkinsonian Agents

Two approaches to the synthesis of para-menthene epoxide ((1S,5S,6R)-4) are developed. The first approach includes a reaction between chlorohydrin 7 and NaH in THF. The second involves the formation of epoxide in the reaction of corresponding diacetate 6 with sodium tert-butoxide. One possible mechanism of this reaction is proposed to explain unexpected outcomes in the regio- and stereospecificity of epoxide (1S,5S,6R)-4 formation. The epoxide ring in (1S,5S,6R)-4 is then opened by various S- and O-nucleophiles. This series of reactions allows for the stereoselective synthesis of diverse derivatives of the monoterpenoid Prottremine 1, a compound known for its antiparkinsonian activity, including promising antiparkinsonian properties.

One-pot nucleophilic substitution-double click reactions of biazides leading to functionalized bis(1,2,3-triazole) derivatives

The nucleophilic substitution of benzylic bromides with sodium azide was combined with a subsequent copper-catalyzed (3 + 2) cycloaddition with terminal alkynes. This one-pot process was developed with a simple model alkyne, but then applied to more complex alkynes bearing enantiopure 1,2-oxazinyl substituents. Hence, the precursor compounds 1,2-, 1,3- or 1,4-bis(bromomethyl)benzene furnished geometrically differing bis(1,2,3-triazole) derivatives. The use of tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) as ligand for the click step turned out to be very advantageous. The compounds with 1,2-oxazinyl end groups can potentially serve as precursors of divalent carbohydrate mimetics, but the reductive cleavage of the 1,2-oxazine rings to aminopyran moieties did not proceed cleanly with these compounds.

Selective Synthesis of Monofluorinated Compounds Applying Amine/HF Reagents

For nucleophilic monofluorination, amine/HF reagents such as Et3 N⋅3HF, Pyr⋅9HF (Olah's reagent) and similar combinations belong to the most frequently used fluoride sources, whereupon the selectivity of these reagents can be very different depending of its acidity, the nucleophilicity of the fluoride equivalent, and the structure of the particular substrate. These reagents can be used safely in ordinary chemistry laboratories for nucleophilic substitution reactions by fluoride at sp3 -hybridized carbon centers. For ring opening reactions of epoxides, the regio- and stereoselectivity is very much depending of the nature of the epoxide and the acidity of the HF reagent favoring either SN 1 or SN 2 type reactions. Similarly, the outcome of halofluorination and similar reactions with sulfur or seleno electrophiles can be controlled by the particular combination of the electrophile and the fluoride source. Examples for the application of these reaction types for the synthesis of fluorine-containing analogues of natural products or biologically relevant compounds are in the focus of this personal account.

Comprehensive Study and Development of a Metal-Free and Mild Nucleophilic Trifluoromethoxylation

Among the general interest in fluorinated compounds, trifluoromethoxylated molecules play a specific role. However, despite this interest, the development of efficient reagents to perform trifluoromethoxylation reactions remains a challenge. Here, 2,4-dinitro-trifluoromethoxybenzene (DNTFB) is used as a trifluoromethoxylating reagent to perform nucleophilic substitution under mild metal-free conditions with different leaving groups, including direct dehydroxytrifluoromethoxylation. A mechanistic study rationalized the reaction and subsequently proposed only three reaction conditions, depending on the reactivity of the starting substrates.

Analogy of the Reactions of Aromatic and Aliphatic π-Electrophiles with Nucleophiles

The aim of this essay is to disclose the similarity of a great variety of reactions that proceed between nucleophiles and π-electrophiles-both aromatic and aliphatic. These reactions proceed via initial reversible addition, followed by a variety of transformations that are common for the adducts of both aliphatic and aromatic electrophiles. We hope that understanding of this analogy should help to expand the scope of the known reactions and inspire the search for new reactions that were overlooked.

Introducing Water and Deep Eutectic Solvents in Organosodium Chemistry: Chemoselective Nucleophilic Functionalizations in Air

Advancing the development of perfecting the use of polar organometallics in bio-inspired solvents, we report on the effective generation in batch of organosodium compounds, by the oxidative addition of a C-Cl bond to sodium, a halogen/sodium exchange, or by direct sodiation, when using sodium bricks or neopentylsodium in hexane as sodium sources. C(sp3)-, C(sp2)-, and C(sp)-hybridized alkyl and (hetero)aryl sodiated species have been chemoselectively trapped (in competition with protonolysis), with a variety of electrophiles when working "on water", or in biodegradable choline chloride/urea or L-proline/glycerol eutectic mixtures, under hydrous conditions and at room temperature. Additional benefits include a very short reaction time (20 s), a wide substrate scope, and good to excellent yields (up to 98%) of the desired adducts. The practicality of the proposed protocol was demonstrated by setting up a sodium-mediated multigram-scale synthesis of the anticholinergic drug orphenadrine.

Deciphering the Differences in Ambident Reactivity between the Cyanate, Thiocyanate Ions, and their P- and As-Containing Analogues

Although the cyanate and thiocyanate anions belong to the most known textbook examples of ambident nucleophiles, the electronic factors that determine their markedly differing reactivities are still unclear. Their recently discovered P- and As-containing [PCX]- and [AsCX]-analogues (X: O, S, Se), whose ambident nature is practically unexplored, may serve as ideal basis for comparison to clarify these differences. Herein we present comprehensive theoretical investigations on the nucleophilic behaviours of the whole set of so far known [ECX]-(E: N, P, As, X: O, S, Se) anions, aiming for a systematic understanding of the reactivity patterns and deciphering the factors that govern the nucleophilic substitutions. Our results indicate that the SN2 reactions of the O-containing [ECO]- ions are thermodynamically preferred at the E pnictogen centres, while the kinetic contributions are only substantial for the N-containing [NCX]-anions. The ambident reactivities of the congeners that contain N or O significantly differ from those with P, As, S, or Se heteroatoms, in line with the inert s-orbital effect, characteristic for the heavier elements. By analysing the electronic structures and bonding patterns of the anions and relevant transition state structures, we offer clear explanations for the differing reactivities of the whole set of [ECX]-anions.

Mechanisms of the Reaction of Elemental Sulfur and Polysulfides with Cyanide and Phosphines

The reactions of elemental sulfur (S8) and polysulfides with nucleophiles are relevant to organic synthesis, materials science and biochemistry, but the mechanisms by which they operate are still unknown due to the inherent thermodynamic and kinetic instability of polysulfide intermediates. Using Density Functional Theory (DFT) calculations at the ωB97X-D/aug-cc-pV(T+d)Z/SMD(MeCN) // ωB97X-D/ aug-cc-pVDZ/SMD(MeCN) level of theory, we studied the mechanisms behind the reaction of elemental sulfur and polysulfides with cyanide and phosphines, which quantitatively generate the monosulfide products thiocyanate and phosphine sulfides, respectively. All plausible pathways including nucleophilic decomposition, unimolecular decomposition, scrambling reactions, and attack on thiosulfoxides, have been considered to provide the first comprehensive mechanistic picture for this class of reactions. Overall, intramolecular cyclization is identified as the most favorable decomposition pathway for long polysulfides. For short polysulfides, a mixture of unimolecular decomposition, nucleophilic attack, and scrambling pathways can be expected.

Traceless N-Polyfluoroalkylation of Weakly Nucleophilic Nitrogen Containing Compounds

Here we report an efficient access to high-value N-polyfluoroalkyl anilines, primary polyfluoroalkylamines and N,N-bis(polyfluoroalkyl)amines, via N-polyfluoroalkylation of sulfonamides and phthalimide derivatives using sulfuryl fluoride (SO2F2). The in situ formation of polyfluoroalkyl fluorosulfonates from commercially available fluorinated alcohols and economical sulfuryl fluoride is highly advantageous given that some polyfluoroalkyl halides are ozone-depleting substances (ODS) regulated by the Montreal protocol. This general method is applied to the polyfluoroalkylation of a variety of sulfonamides, N-sulfonyl carbamates and phthalimide with a wide tolerance of functional groups. The process thus provides viable access for industry to N-(polyfluoroalkyl)anilines as well as primary and secondary N-(polyfluoroalkyl)amines, which are very valuable but not easily accessible building blocks for life science applications.

The Transformation of Inorganic to Organic Carbonates: Chasing for Reaction Pathways in Mechanochemistry

Mechanochemical reactions are solvent-free alternatives to solution-based syntheses enabling even conventionally impossible transformations. Their reaction pathways, however, usually remain unexplored within the heavily vibrating, dense milling vessels. Here, we showcase how the green organic solvent diethyl carbonate is synthesized mechanochemically from inorganic alkali carbonates and how the complementary combination of milling parameter studies, synchrotron X-ray diffraction real time monitoring, and quantum chemical calculations reveal the underlying reaction pathways. With this, reaction intermediates are identified, and chemical concepts of solution-chemistry are challenged or corroborated for mechanochemistry.

Straightforward and Efficient Protocol for the Synthesis of Pyrazolo [4,3-b]pyridines and Indazoles

An efficient method for the synthesis of pyrazolo [4,3-b]pyridines has been developed on the basis of readily available 2-chloro-3-nitropyridines via a sequence of SNAr and modified Japp-Klingemann reactions. The method offers a number of advantages including utilization of stable arenediazonium tosylates, operational simplicity as well as combining the azo-coupling, deacylation and pyrazole ring annulation steps in a one-pot manner. An unusual rearrangement (C-N-migration of the acetyl group) was observed and a plausible mechanism was proposed based on the isolated intermediates and NMR experiments. In addition, the developed protocol was successfully applied to the synthesis of 1-arylindazoles combining the Japp-Klingemann reaction and cyclization of the resulting hydrazone as a one-pot procedure.

Functionalization of Conductive Polymers through Covalent Postmodification

Organic chemical reactions have been used to functionalize preformed conducting polymers (CPs). The extensive work performed on polyaniline (PANI), polypyrrole (PPy), and polythiophene (PT) is described together with the more limited work on other CPs. Two approaches have been taken for the functionalization: (i) direct reactions on the CP chains and (ii) reaction with substituted CPs bearing reactive groups (e.g., ester). Electrophilic aromatic substitution, S_EAr, is directly made on the non-conductive (reduced form) of the CPs. In PANI and PPy, the N-H can be electrophilically substituted. The nitrogen nucleophile could produce nucleophilic substitutions (SN) on alkyl or acyl groups. Another direct reaction is the nucleophilic conjugate addition on the oxidized form of the polymer (PANI, PPy or PT). In the case of PT, the main functionalization method was indirect, and the linking of functional groups via attachment to reactive groups was already present in the monomer. The same is the case for most other conducting polymers, such as poly(fluorene). The target properties which are improved by the functionalization of the different polymers is also discussed.

Synthesis and Reactions of 3-Halogenated 2-CF(3)-Indoles

Halogenation of 2-trifluoromethylindole afforded 3-chloro-, 3-bromo- and 3-iodo derivatives in up to 98% yield. Methyl-, benzyl- and tosyl-groups can be installed at the nitrogen atom of prepared indoles in high yields by base catalyzed reaction with the corresponding alkylating (sulfonylating) reagents. A high synthetic utility of the prepared haloindoles in the reaction with various nucleophilies was shown. The reaction with 4-methylthiophenol and copper cyanide afforded the corresponding sulfides and nitriles in high yield. Palladium catalyzed cross-coupling with phenyl boronic acid and phenylacetylene gave the corresponding 3-phenyl-2-CF₃-indoles and acetylenic derivatives in 72-98% yield.

Charge-Transfer Transitions Govern the Reactivity and Photophysics of Vicinally Diphosphanyl-Substituted Diborapentacenes

2,3-Difluoro-5,14-dihydro-5,14-diborapentacene (DBP) was endowed with two vicinal Ph₂ P groups by an S_N Ar reaction at both CF sites using Ph₂ PSiMe₃ . Computations reveal the ambipolar product P to undergo P-to-B charge transfer under ambient light irradiation. Consequently, P is prone to photooxidation by air, yielding the Ph₂ P(O) species PO. With S₈ or [Me₃ O][BF₄ ], P furnishes the Ph₂ P(S) or Ph₂ P(Me)⁺ derivatives PS or [PMe][BF₄ ]₂ . Along the series P, PO, PS, and [PMe][BF₄ ]₂ , the redox potentials shift anodically from E_1/2 =-1.89 V to -1.02 V (CH₂ Cl₂ ). Thus, derivatization of the Ph₂ P group allows late-stage modulation of the LUMO-energy level of the DBP. Derivatization also influences the emission properties of the compounds, as PO shows green (521 nm) and [PMe][BF₄ ]₂ red (622 nm) fluorescence in C₆ H₆ , while P and PS are dark. With CuBr and AgBr, P forms dimeric [M(μ-Br)]₂ complexes [PCu]₂ and [PAg]₂ , which show pronounced metal-to-ligand charge transfer (MLCT), making P a promising ligand for photocatalysts.

Spectroscopic Study of the Br- +CH3 I→I- +CH3 Br SN 2 Reaction

Mass spectrometry and anion photoelectron spectroscopy have been used to study the gas-phase <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>S</mml:mi> <mml:mi>N</mml:mi></mml:msub> <mml:mn>2</mml:mn></mml:mrow> <mml:annotation>${{{\rm S}}_{{\rm N}}2}$</mml:annotation> </mml:semantics> </mml:math> reaction involving <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msup><mml:mrow><mml:mi>B</mml:mi> <mml:mi>r</mml:mi></mml:mrow> <mml:mo>-</mml:mo></mml:msup> <mml:annotation>${{{\rm B}{\rm r}}^{-}}$</mml:annotation> </mml:semantics> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow> <mml:msub><mml:mrow><mml:mi>C</mml:mi> <mml:mi>H</mml:mi></mml:mrow> <mml:mn>3</mml:mn></mml:msub> <mml:mi>I</mml:mi></mml:mrow> <mml:annotation>${{{\rm C}{\rm H}}_{3}{\rm I}}$</mml:annotation> </mml:semantics> </mml:math> . The anion photoelectron spectra associated with the reaction intermediates of this <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>S</mml:mi> <mml:mi>N</mml:mi></mml:msub> <mml:mn>2</mml:mn></mml:mrow> <mml:annotation>${{{\rm S}}_{{\rm N}}2}$</mml:annotation> </mml:semantics> </mml:math> reaction are presented. High-level CCSD(T) calculations have been utilised to investigate the reaction intermediates that may form as a result of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>S</mml:mi> <mml:mi>N</mml:mi></mml:msub> <mml:mn>2</mml:mn></mml:mrow> <mml:annotation>${{{\rm S}}_{{\rm N}}2}$</mml:annotation> </mml:semantics> </mml:math> reaction along various different reaction pathways, including back-side attack and front-side attack. In addition, simulated vertical detachment energies of each reaction intermediate have been calculated to rationalise the photoelectron spectra.

Rational Tuning of the Reactivity of Three-Membered Heterocycle Ring Openings via SN 2 Reactions

The development of small-molecule covalent inhibitors and probes continuously pushes the rapidly evolving field of chemical biology forward. A key element in these molecular tool compounds is the "electrophilic trap" that allows a covalent linkage with the target enzyme. The reactivity of this entity needs to be well balanced to effectively trap the desired enzyme, while not being attacked by off-target nucleophiles. Here we investigate the intrinsic reactivity of substrates containing a class of widely used electrophilic traps, the three-membered heterocycles with a nitrogen (aziridine), phosphorus (phosphirane), oxygen (epoxide) or sulfur atom (thiirane) as heteroatom. Using quantum chemical approaches, we studied the conformational flexibility and nucleophilic ring opening of a series of model substrates, in which these electrophilic traps are mounted on a cyclohexene scaffold (C₆ H₁₀ Y with Y=NH, PH, O, S). It was revealed that the activation energy of the ring opening does not necessarily follow the trend that is expected from C-Y leaving-group bond strength, but steeply decreases from Y=NH, to PH, to O, to S. We illustrate that the HOMO_Nu -LUMO_Substrate interaction is an all-important factor for the observed reactivity. In addition, we show that the activation energy of aziridines and phosphiranes can be tuned far below that of the corresponding epoxides and thiiranes by the addition of proper electron-withdrawing ring substituents. Our results provide mechanistic insights to rationally tune the reactivity of this class of popular electrophilic traps and can guide the experimental design of covalent inhibitors and probes for enzymatic activity.

New 5-Aminotetrazole-Based Energetic Polymers: Synthesis, Structure and Properties

An N-glycidyl-5-aminotetrazole homopolymer was synthesized herein by nucleophilic substitution of 5-aminotetrazole heterocycles for chlorine atoms in poly-(epichlorohydrin)-butanediol. Copolymers of N-glycidyl-5-aminotetrazole and glycidyl azide with a varied ratio of energetic elements were synthesized by simultaneously reacting the 5-aminotetrazole sodium salt and the azide ion with the starting polymeric matrix. The 5-aminotetrazole-based homopolymer was nitrated to furnish a polymer whose macromolecule is enriched additionally with energy-rich terminal ONO₂ groups and nitrate anions. The structures of the synthesized polymers were characterized by ¹H and ¹³C NMR and IR spectroscopies, elemental analysis and gel-permeation chromatography. The densities were experimentally measured, and thermal stability data were acquired by differential scanning calorimetry. The insertion of aminotetrazole heterocycles into the polymeric chain and their modification via nitration provides an acceptable thermal stability and a considerable enhancement in density and nitrogen content compared to azide homopolymer GAP. By the 1.3-dipolar cycloaddition reaction, we demonstrated the conceptual possibility of preparing spatially branched, energy-rich polymeric binders bearing 5-aminotetrazole and 1,2,3-triazole heterocycles starting from the plasticized azide copolymers. The presence of the aforesaid advantages makes the reported polymers attractive candidates for use as a scaffold of energetic binders.

Selective Csp3-F Bond Functionalization with Lithium Iodide

A highly efficient method for C-F bond functionalization of a broad variety of activated and unactivated aliphatic substrates with inexpensive lithium iodide is presented. Primary, secondary, tertiary, benzylic, propargylic and α-functionalized alkyl fluorides react in chlorinated or aromatic solvents at room temperature or upon heating to the corresponding iodides which are isolated in 91-99% yield. The reaction is selective for aliphatic monofluorides and can be coupled with in situ nucleophilic iodide replacements to install carbon-carbon, carbon-nitrogen and carbon-sulfur bonds with high yields. Alkyl difluorides, trifluorides, even in activated benzylic positions, are inert under the same conditions and aryl fluoride bonds are also tolerated.

Nucleophilic Functionalization of 2-R-3-Nitropyridines as a Versatile Approach to Novel Fluorescent Molecules

A number of new 2-methyl- and 2-arylvinyl-3-nitropyridines were synthesized and their reactions with thiols were studied. It was found that 3-NO₂ tends to be selectively substituted under the action of sulfur nucleophiles in the presence of another nucleofuge in position 5. Correlations between the substitution pattern and regioselectivity as well as photophysical properties were established. Some synthesized compounds possessed a large Stokes shift.

Investigations on the Synthesis, Reactivity, and Properties of Perfluoro-α-Benzo-Fused BOPHY Fluorophores

The synthesis and reactivity of 3,8-dibromo-dodecafluoro-benzo-fused BOPHY 2 are reported, via S_N Ar with O-, N- S- and C-nucleophiles, and in Pd(0)-catalyzed cross-coupling reactions (Suzuki and Stille). The resulting perfluoro-BOPHY derivatives were investigated for their reactivity in the presence of various nucleophiles. BOPHY 3 displays reversible color change and fluorescence quenching in the presence of bases (Et₃ N, DBU), whereas BOPHY 7 reacts preferentially at the α-pyrrolic positions, and BOPHY 8 undergoes regioselective fluorine substitution in the presence of thiols. The structural and electronic features of the fluorinated BOPHYs were studied by TD-DFT computations. In addition, their spectroscopic and cellular properties were investigated; BOPHY 10 shows the most red-shifted absorption/emission (λ_max 659/699 nm) and 7 the highest fluorescence (Φ_f =0.95), while all compounds studied showed low cytotoxicity toward human HEp2 cells and were efficiently internalized.

An Orthogonal Synthetic Approach to Nonsymmetrical Bisazolyl 2,4,6-Trisubstituted Pyridines

A three-step synthetic route giving access to nonsymmetrical bisazolyl 2,4,6-trisubstituted pyridines with different substituents on the pyrazole, indazole, and pyridine heterocycles is described. From the readily available 4-bromo-2,6-difluoropyridine, both fluorine atoms allow for easy selective stepwise substitution, and the bromine atom provides easy access to additional functionalities through both Suzuki and Sonogashira Pd(0) cross-coupling reactions. These synthons represent optimal structures as building blocks in complexation and metalloorganic structures for the tuning of their chelating and photophysical properties.

Mechanochemical Nucleophilic Substitution of Alcohols via Isouronium Intermediates

An expansion of the solvent-free synthetic toolbox is essential for advances in the sustainable chemical industry. Mechanochemical reactions offer a superior safety profile and reduced amount of waste compared to conventional solvent-based synthesis. Herein a new mechanochemical method was developed for nucleophilic substitution of alcohols using fluoro-N,N,N',N'-tetramethylformamidinium hexafluorophosphate (TFFH) and K₂ HPO₄ as an alcohol-activating reagent and a base, respectively. Alcohol activation and reaction with a nucleophile were performed in one milling jar via reactive isouronium intermediates. Nucleophilic substitution with amines afforded alkylated amines in 31-91 % yields. The complete stereoinversion occurred for the S_N 2 reaction of (R)- and (S)-ethyl lactates. Substitution with halide anions (F^- , Br^- , I^- ) and oxygen-centered (CH₃ OH, PhO^- ) nucleophiles was also tested. Application of the method to the synthesis of active pharmaceutical ingredients has been demonstrated.

Nucleophilic Substitution Reactions in the [B3H8]- Anion in the Presence of Lewis Acids

As a result of our study on the interaction between the octahydrotriborate anion with nucleophiles (Nu = THF, Ph₃P, Ph₂P-(CH₂)₂-PPh₂ (dppe), Ph₃As, Et₃N, PhNH₂, C₅H₅N, CH₃CN, Ph₂CHCN)) in the presence of a wide range of Lewis acids (Ti(IV), Hf(IV), Zr(IV), Al, Cu(I), Zn, Mn(II), Co(II) halides and iodine), a number of substituted derivatives of the octahydrotriborate anion [B₃H₇Nu] are obtained. It is found that the use of TiCl₄, AlCl₃, ZrCl₄, HfCl₄, CuCl and iodine leads to the highest product yields. In this case, it is most likely that the reaction proceeds through the formation of an intermediate [B₃H₇-HMXn_x], which was detected by NMR spectroscopy. The structures of [Ph₃P·B₃H₇] and [PhNH₂·B₃H₇] were determined by X-ray diffraction.

Nucleophilic Substitution at Heteroatoms-Identity Substitution Reactions at Phosphorus and Sulfur Centers: Do They Proceed in a Concerted (SN2) or Stepwise (A-E) Way?

The mechanisms of three selected identity substitution reactions at phosphorus and sulfur occurring with stereospecific inversion have been investigated using density functional theory (DFT). The first identity reaction between methoxyl anion and methyl ethylphenylphosphinate 1 reported in 1963 has been shown to proceed in a stepwise fashion according to the addition-elimination (A-E) mechanism involving formation of a pentacoordinate phosphorus intermediate (TBI-1). In contrast, the results of DFT studies of the identity chloride exchange reaction in (ethoxy)ethylphosphonochloridothionate 3 in acetone solution provided evidence that it proceeds synchronously according to the classical Ingold's S_N2-P mechanism. DFT calculations of the methoxyl-methoxy exchange reaction at sulfur in methyl p-toluenesulfinate 4 catalyzed by trifluoroacetic acid in methanol revealed that it proceeds stepwise (A-E mechanism), involving the formation of the high-coordinate sulfurane intermediate. In both identity transesterification reactions, 1 and 4, the transiently formed trigonal bipyramidal intermediates with the two methoxyl groups occupying apical positions (TBI-1 and TBI-4) have higher free energy barriers for the Berry-type pseudorotation than those for direct decomposition to starting phosphinate and sulfinate ensuring stereospecific inversion of configuration at the phosphinyl and sulfinyl centers. Thus, the DFT method proved its usefulness in the distinction between both mechanisms that are often indistinguishable by kinetic measurements.

Mechanistic Understanding of Superoxide Radical-Mediated Degradation of Perfluorocarboxylic Acids

Perfluorocarboxylic acids (PFCAs) exhibit strong persistence in sunlit surface waters and in radical-based treatment processes, where superoxide radical (O₂^•-) is an important and abundant reactive oxygen species. Given that the role of O₂^•- during the transformation of PFCAs remains largely unknown, we investigated the kinetics and mechanisms of O₂^•--mediated PFCAs attenuation through complementary experimental and theoretical approaches. The aqueous-phase rate constants between O₂^•- and C3-C8 PFCAs were measured using a newly designed in situ spectroscopic system. Mechanistically, bimolecular nucleophilic substitution (S_N2) is most likely to be thermodynamically feasible, as indicated by density functional theory calculations at the CBS-QB3 level of theory. This pathway was then investigated by ab initio molecular dynamics simulation with free-energy samplings. As O₂^•- approaches PFCA, the C-F bond at the alpha carbon is spontaneously stretched, leading to the bond cleavage. The solvation mechanism for O₂^•--mediated PFCA degradation was also elucidated. Our results indicated that although the less polar solvent enhanced the nucleophilicity of O₂^•-, it also decreased the desolvation process of PFCAs, resulting in reduced kinetics. With these quantitative and mechanistic results, we achieved a defined picture of the O₂^•--initiated abatement of PFCAs in natural and engineered waters.

Simplified and accessible [18 F]F-AraG synthesis procedure for preclinical PET

The PET tracer [¹⁸ F]F-AraG, an arabinosyl guanine analog, has shown promise for visualizing activated T cells in multiple diseases. Herein, a practitioner's protocol is described, in which the PET tracer is prepared using minimal equipment and manual actions, making it widely accessible for preclinical applications.

Inherent Reactivity of Spiro-Activated Electrophilic Cyclopropanes

The kinetics of the ring‐opening reactions of thiophenolates with geminal bis(acceptor)‐substituted cyclopropanes in DMSO at 20 °C was monitored by photometric methods. The determined second‐order rate constants of the S_N2 reactions followed linear relationships with Mayr nucleophilicity parameters (N/s_N) and Brønsted basicities (pK_aH) of the thiophenolates as well as with Hammett substituent parameters (σ) for groups attached to the thiophenolates. Phenyl‐substituted cyclopropanes reacted by up to a factor of 15 faster than their unsubstituted analogues, in accord with the known activating effect of adjacent π‐systems in S_N2 reactions. Variation of the electronic properties of substituents at the phenyl groups of the cyclopropanes gave rise to parabolic Hammett relationships. Thus, the inherent S_N2 reactivity of electrophilic cyclopropanes is activated by electron‐rich π‐systems because of the more advanced C1−C2 bond polarization in the transition state. On the other hand, electron‐poor π‐systems also lower the energetic barriers for the attack of anionic nucleophiles owing to attractive electrostatic interactions.

Rational Design 2-Hydroxypropylphosphonium Salts as Cancer Cell Mitochondria-Targeted Vectors: Synthesis, Structure, and Biological Properties

It has been shown for a wide range of epoxy compounds that their interaction with triphenylphosphonium triflate occurs with a high chemoselectivity and leads to the formation of (2-hydroxypropyl)triphenylphosphonium triflates 3 substituted in the 3-position with an alkoxy, alkylcarboxyl group, or halogen, which were isolated in a high yield. Using the methodology for the disclosure of epichlorohydrin with alcohols in the presence of boron trifluoride etherate, followed by the substitution of iodine for chlorine and treatment with triphenylphosphine, 2-hydroxypropyltriphenylphosphonium iodides 4 were also obtained. The molecular and supramolecular structure of the obtained phosphonium salts was established, and their high antitumor activity was revealed in relation to duodenal adenocarcinoma. The formation of liposomal systems based on phosphonium salt 3 and L-α-phosphatidylcholine (PC) was employed for improving the bioavailability and reducing the toxicity. They were produced by the thin film rehydration method and exhibited cytotoxic properties. This rational design of phosphonium salts 3 and 4 has promising potential of new vectors for targeted delivery into mitochondria of tumor cells.

A Potential Iterative Approach to 1,4-Dihydro-N-Heteroacene Arrays

A new method for the synthesis of substituted 1,4‐dihydrophenazines is reported and the structure of N‐butyl‐5‐methyl‐3‐nitro‐5,10‐dihydrophenazine is proven by an X‐ray single‐crystal structure determination.

18F-Fluorination Using Tri-Tert-Butanol Ammonium Iodide as Phase-Transfer Catalyst: An Alternative Minimalist Approach

The ¹⁸F syntheses of tracers for positron emission tomography (PET) typically require several steps, including extraction of [¹⁸F]fluoride from H₂[¹⁸O]O, elution, and drying, prior to nucleophilic substitution reaction, being a laborious and time-consuming process. The elution of [¹⁸F]fluoride is commonly achieved by phase transfer catalysts (PTC) in aqueous solution, which makes azeotropic drying indispensable. The ideal PTC is characterized by a slightly basic nature, its capacity to elute [¹⁸F]fluoride with anhydrous solvents, and its efficient complex formation with [¹⁸F]fluoride during subsequent labeling. Herein, we developed tri-(tert-butanol)-methylammonium iodide (TBMA-I), a quaternary ammonium salt serving as the PTC for ¹⁸F-fluorination reactions. The favorable elution efficiency of [¹⁸F]fluoride using TBMA-I was demonstrated with aprotic and protic solvents, maintaining high ¹⁸F-recoveries of 96-99%. ¹⁸F-labeling reactions using TBMA-I as PTC were studied with aliphatic 1,3-ditosylpropane and aryl pinacol boronate esters as precursors, providing ¹⁸F-labeled products in moderate-to-high radiochemical yields. TBMA-I revealed adequate properties for application to ¹⁸F-fluorination reactions and could be used for elution of [¹⁸F]fluoride with MeOH, omitting an additional base and azeotropic drying prior to ¹⁸F-labeling. We speculate that the tert-alcohol functionality of TBMA-I promotes intermolecular hydrogen bonding, which enhances the elution efficiency and stability of [¹⁸F]fluoride during nucleophilic ¹⁸F-fluorination.

Effect of the Nucleophile's Nature on Chloroacetanilide Herbicides Cleavage Reaction Mechanism. A DFT Study

In this study, the degradation mechanism of chloroacetanilide herbicides in the presence of four different nucleophiles, namely: Br^-, I^-, HS^-, and S₂O₃^-2, was theoretically evaluated using the dispersion-corrected hybrid functional wB97XD and the DGDZVP as a basis set. The comparison of computed activation energies with experimental data shows an excellent correlation (R² = 0.98 for alachlor and 0.97 for propachlor). The results suggest that the best nucleophiles are those where a sulfur atom performs the nucleophilic attack, whereas the other species are less reactive. Furthermore, it was observed that the different R groups of chloroacetanilide herbicides have a negligible effect on the activation energy of the process. Further insights into the mechanism show that geometrical changes and electronic rearrangements contribute 60% and 40% of the activation energy, respectively. A deeper analysis of the reaction coordinate was conducted, employing the evolution chemical potential, hardness, and electrophilicity index, as well as the electronic flux. The charge analysis shows that the electron density of chlorine increases as the nucleophilic attack occurs. Finally, NBO analysis indicates that the nucleophilic substitution in chloroacetanilides is an asynchronous process with a late transition state for all models except for the case of the iodide attack, which occurs through an early transition state in the reaction.

Stabilization of the Elusive 9-Carbene-9-Borafluorene Monoanion

Two-electron reduction of carbene-supported 9-bromo-9-borafluorenes with excess KC₈ , Na, or Li-naphthalenide affords six N-heterocyclic carbene (NHC)- or cyclic(alkyl)(amino) carbene (CAAC)-stabilized borafluorene anions (3-8)-the first isolated and structurally authenticated examples of the elusive 9-carbene-9-borafluorene monoanion. The electronic structure, bonding, and aromaticity of the boracyclic anions were comprehensively investigated via computational studies. Compounds 5 and 8 react with metal halides via salt elimination to give new B-E (E=Au, Se, Ge)-containing materials (9-12). Upon reaction with diketones, the carbene ligand cleanly dissociates from 5 or 8 to yield new B-O containing spirocycles (13-14) that cannot be easily obtained using "normal" valent borafluorene compounds. Collectively, these results support the notion that carbene-stabilized monoanionic borafluorenes may serve as a new platform for the one-step construction of higher-value boracyclic materials.

Fifty years of nucleophilic substitution in the gas phase

Bimolecular nucleophilic substitution ( S N 2 ) reactions have become a model system for the investigation of structure-reactivity relationships, stereochemistry, solvent influences, and detailed atomistic dynamics. In this review, the progress during five decades of experimental and theoretical research on gas phase S N 2 reactions is discussed. Many advancements of the employed methods have led to a tremendous increase in our understanding of the properties and the dynamics of these reactions. For reactions involving six atoms a quantitative agreement of the differential reactive scattering cross sections has already been achieved, in the future it is expected that even larger polyatomic reactions systems become tractable. Furthermore, studies with higher precision, improved reactant control, and a more accurate theoretical treatment of quantum effects are envisioned.

Smart On-Site Immobilizable Near-Infrared II Fluorescent Nanoprobes for Ultra-Long-Term Imaging-Guided Tumor Surgery and Photothermal Therapy

Accurate diagnosis and efficient treatment of tumors are highly significant in battling cancer. Near-infrared II (NIR-II) fluorescence imaging shows big promise for deep tumor visualization in living systems due to high temporal and spatial resolution and deep tissue penetration capability, whereas the development of efficient NIR-II probes for tumor theranostics still faces a huge challenge. Herein, we have designed and constructed intelligent mPEG₅₀₀₀-PCL₃₀₀₀-encapsulated NIR-II nanoprobe ZM1068-NPs that showed great chemical stability and excellent biocompatibility. With the merits of the strong fluorescence in the NIR-II region and prominent optical-thermal conversion efficiency, this probe was successfully used for NIR-II imaging-guided surgery and photothermal therapy of breast carcinoma in living mice. More notably, it was for the first time found that ZM1068 dyes could be covalently on-site-immobilized within tumors through the thiol-chlor nucleophilic substitution reaction, resulting in improved tumor accumulation and retention time. We thus envision that this probe may provide an attractive means for precise cancer diagnosis and treatment.

Sterically Facilitated Intramolecular Nucleophilic NMe2 Group Substitution in the Synthesis of Fused Isoxazoles: Theoretical Study

The influence of steric repulsion between the NMe₂ group and a second ortho-(peri-)substituent in the series of 1-dimethylaminonaphthalene and N,N-dimethylanilene ortho-oximes on the ease of the NMe₂ group’s intramolecular nucleophilic substitution is studied. Possible reaction intermediates for three mechanisms are calculated (ωB97xd/def-2-TZVP), and their free Gibbs energies are compared to model reaction profiles. Supporting experiments have proved the absence of studied reactivity in the case of simple 2-dimethylaminobenzaldoxime, which allowed us to establish reactivity limits. The significant facilitation of NMe₂ group displacement in the presence of bulky substituents is demonstrated. The possibility of fused isoxazoles synthesis via the intramolecular nucleophilic substitution of a protonated NMe₂ group in the aniline and naphthalene series is predicted.

Metal-free nucleophilic trifluoromethylselenolation via an iodide-mediated umpolung reactivity of trifluoromethylselenotoluenesulfonate

We report herein a practical method to generate CF₃Se^- (and R_FSe^-) anions from shelf-stable reagents under iodide activation. Metal-free nucleophilic trifluoromethylselenolations have been then performed with this in situ-generated anion. Perfluoroalkylselenolations have also been described.

Synthesis of Naphthoquinone Derivatives: Menaquinones, Lipoquinones and Other Vitamin K Derivatives

Menaquinones are a class of isoprenoid molecules that have important roles in human biology and bacterial electron transport, and multiple methods have been developed for their synthesis. These compounds consist of a methylnaphthoquinone (MK) unit and an isoprene side chain, such as found in vitamin K₁ (phylloquinone), K₂, and other lipoquinones. The most common naturally occurring menaquinones contain multiple isoprene units and are very hydrophobic, rendering it difficult to evaluate the biological activity of these compounds in aqueous assays. One way to overcome this challenge has been the application of truncated MK-derivatives for their moderate solubility in water. The synthesis of such derivatives has been dominated by Friedel-Crafts alkylation with BF₃∙OEt₂. This attractive method occurs over two steps from commercially available starting materials, but it generally produces low yields and a mixture of isomers. In this review, we summarize reported syntheses of both truncated and naturally occurring MK-derivatives that encompass five different synthetic strategies: Nucleophilic ring methods, metal-mediated reactions, electrophilic ring methods, pericyclic reactions, and homologation and side chain extensions. The advantages and disadvantages of each method are discussed, identifying methods with a focus on high yields, regioselectivity, and stereochemistry leading to a detailed overview of the reported chemistry available for preparation of these compounds.

Occurrence of the Plant Growth Regulator Chlormequat in Food May Be Due to Natural Formation: A Preliminary Mechanistic Study

The study reports the role of choline and compounds thereof in the formation of chlormequat under thermal conditions, with emphasis on the molecular mechanism involved in the transformation. The data show the decomposition of choline to chlormequat at 200 °C in presence of chloride ions, likely by nucleophilic substitution. Furthermore, the results suggest that phosphatidylcholine, glycerophosphocholine, and phosphocholine are the effective precursors of chlormequat under sufficient thermal conditions due to their capability to degrade to choline and/or the ability of the phosphate moiety to behave as a good leaving group with respect to nucleophilic attacks. Thermal treatments (120 and 200 °C) applied to egg powder, rich in phosphatidylcholine, and wheat flour, with choline at a substantial level, suggest that less energy is required for obtaining chlormequat from phosphatidylcholine than from choline. This observation is consistent with the postulated mechanism of a nucleophilic substitution with phosphate moieties acting as better leaving groups than the hydroxyl group.

Thietanyl Protection in the Synthesis of 8-Substituted 1-Benzyl-3-methyl-3,7-dihydro- 1H-purine-2,6-diones

AIM AND OBJECTIVE

1-Аlkyl-3,7-dihydro-1H-purine-2,6-diones containing no substituents in the N7 position can be synthesized only using protecting groups, for example, benzyl protection. However, in the case of synthesis of 1-benzyl-3,7-dihydro-1H-purine-2,6-diones, the use of benzyl protection may lead to simultaneous debenzylation of both N1 and N7 positions. Therefore, it is necessary to use other protective groups for the synthesis of 1-benzyl-3,7-dihydro-1H-purine-2,6-diones.

MATERIALS AND METHODS

8-Bromo- and 8-amino-substituted 1-benzyl-3-methyl-3,7-dihydro-1H-purine-2,6-diones unsubstituted in the N7 position were synthesized with the use of thietanyl protecting group. The thietane ring was introduced via the reaction of 8-bromo-3-methyl-3,7-dihydro-1H-purine-2,6-dione with 2-chloromethylthiirane, giving rise to 8-bromo-3-methyl-7-(thietan-3-yl)-3,7-dihydro-1H-purine-2,6-dione. The subsequent alkylation with benzyl chloride yielded 1-benzyl-8-bromo-3-methyl-7-(thietan-3-yl)-3,7-dihydro-1H-purine-2,6-dione, which was oxidized with hydrogen peroxide to be converted to 1-benzyl-8-bromo-3-methyl-7-(1,1-dioxothietan- 3-yl)-3,7-dihydro-1H-purine-2,6-dione. This product reacted with amines to give 8-amino-substituted 1-benzyl-3- methyl-7-(1,1-dioxothietan-3-yl)-3,7-dihydro-1H-purine-2,6-diones. The reaction of 8-substituted 1-benzyl-3- methyl-7-(1,1-dioxothietan-3-yl)-3,7-dihydro-1H-purine-2,6-diones with sodium isopropoxide resulted in the removal of the thietanyl protection and afforded target 8-substituted 1-benzyl-3-methyl-3,7-dihydro-1H-purine-2,6- diones. The structures of the targets compounds have been deduced upon their elemental analysis and spectral data (IR, 1H NMR, 13C NMR and 15N NMR).

RESULTS AND DISCUSSION

A new 8-substituted 1-benzyl-3-methyl-3,7-dihydro-1H-purine-2,6-diones unsubstituted in the N7 position were synthesized using thietanyl protecting group.

CONCLUSION

The present study described a new route to synthesize some new 1,8-disubstituted 3-methyl-3,7- dihydro-1H-purine-2,6-diones unsubstituted in the N7 position starting from available 8-bromo-3-methyl-3,7- dihydro-1H-purine-2,6-dione with use of thietanyl protecting group. The advantages of this protocol are the possibility of the synthesis of 1-benzyl-substituted 3,7-dihydro-1H-purine-2,6-diones, the stability of the thietanyl protecting group upon nucleophilic substitution by amines of the bromine atom in the position 8, as well as mild conditions, and simple execution of experiments.

Polyhalonitrobutadienes as Versatile Building Blocks for the Biotargeted Synthesis of Substituted N-Heterocyclic Compounds

Substituted nitrogen heterocycles are structural key units in many important pharmaceuticals. A new synthetic approach towards heterocyclic compounds displaying antibacterial activity against Staphylococcus aureus or cytotoxic activity has been developed. The selective synthesis of a series of 64 new N-heterocycles from the three nitrobutadienes 2-nitroperchloro-1,3-butadiene, 4-bromotetrachloro-2-nitro-1,3-butadiene and (Z)-1,1,4-trichloro-2,4-dinitrobuta-1,3-diene proved feasible. Their reactions with N-, O- and S-nucleophiles provide rapid access to push-pull substituted benzoxazolines, benzimidazolines, imidazolidines, thiazolidinones, pyrazoles, pyrimidines, pyridopyrimidines, benzoquinolines, isothiazoles, dihydroisoxazoles, and thiophenes with unique substitution patterns. Antibacterial activities of 64 synthesized compounds were examined. Additionally, seven compounds (thiazolidinone, nitropyrimidine, indole, pyridopyrimidine, and thiophene derivatives) exhibited a significant cytotoxicity with IC₅₀-values from 1.05 to 20.1 µM. In conclusion, it was demonstrated that polyhalonitrobutadienes have an interesting potential as structural backbones for a variety of highly functionalized, pharmaceutically active heterocycles.

Regioselective Mono- and Dialkylation of [6,6]-open C60 (CF2 ): Synthetic and Kinetic Aspects

Alkylation of homofullerene [6,6]-C₆₀ (CF₂ )^2- dianion with the set of alkyl halides, RX, was established to demonstrate an effect of RX nature on the conversion, product composition, and regioselectivity. The respective C₆₀ (CF₂ )RH, C₆₀ (CF₂ )R₂ and C₆₀ (CF₂ )R'R'' compounds were obtained in the reaction with sterically unhindered RX, isolated by HPLC and unequivocally characterized. The kinetic studies evidenced S_N 2 mechanism for both alkylation steps, yielding mono- and dialkylated C₆₀ (CF₂ ), respectively, and indicated the negative charge localization at the bridgehead carbon atoms as well as a steric hindrance of the CF₂ moiety likely to be a key factors for the S_N 2 reaction mechanism and observed regioselectivity. The significant difference in the rate constants of the first and the second steps is attributed to the different activation barriers predicted by DFT calculations which makes possible to develop synthetic methods for the regioselective preparation of monoalkylated C₆₀ (CF₂ )RH and heterodialkylated C₆₀ (CF₂ )R'R'' derivatives.

Activation of Aromatic C-F Bonds by a N-Heterocyclic Olefin (NHO)

A N-heterocyclic olefin (NHO), a terminal alkene selectively activates aromatic C-F bonds without the need of any additional catalyst. As a result, a straightforward methodology was developed for the formation of different fluoroaryl-substituted alkenes in which the central carbon-carbon double bond is in a twisted geometry.

Comparison of Substituting Ability of Nitronate versus Enolate for Direct Substitution of a Nitro Group

α-Nitrocinnamate underwent the conjugate addition of an active methylene compound such as nitroacetate, 1,3-dicarbonyl compound, or α-nitroketone, and the following ring closure afforded functionalized heterocyclic frameworks. The reaction of cinnamate with nitroacetate occurs via nucleophilic substitution of a nitro group by the O-attack of the nitronate, which results in isoxazoline N-oxide. This protocol was applicable to 1,3-dicarbonyl compounds to afford dihydrofuran derivatives, including those derived from direct substitution of a nitro group caused by O-attack of enolate. It was found the reactivity was lowered by an electron-withdrawing group on the carbonyl moiety. When α-nitroketone was employed as a substrate, three kinds of products were possibly formed; of these, only isoxazoline N-oxide was identified. This result indicates that the substituting ability of nitronate is higher than that of enolate for the direct S_N2 substitution of a nitro group.

Synthesis of Cyclic Sulfite Diesters and their Evaluation as Sulfur Dioxide (SO2 ) Donors

Although sulfur dioxide (SO₂ ) finds widespread use in the food industry as its hydrated sulfite form, a number of aspects of SO₂ biology remain to be completely understood. Of the tools available for intracellular enhancement of SO₂ levels, most suffer from poor cell permeability and a lack of control over SO₂ release. We report 1,2-cyclic sulfite diesters as a new class of reliable SO₂ donors that dissociate in buffer through nucleophilic displacement to produce SO₂ with tunable release profiles. We provide data in support of the suitability of these SO₂ donors to enhance intracellular SO₂ levels more efficiently than sodium bisulfite, the most commonly used SO₂ donor for cellular studies.

Regio- and stereoselective synthesis of new ensembles of diversely functionalized 1,3-thiaselenol-2-ylmethyl selenides by a double rearrangement reaction

The reaction of 2-(bromomethyl)-1,3-thiaselenole with potassium selenocyanate proceeded via a rearrangement with ring expansion, leading to a six-membered 2,3-dihydro-1,4-thiaselenin-2-yl selenocyanate (kinetic product) which in turn underwent rearrangement with ring contraction to a 1,3-thiaselenol-2-ylmethyl selenocyanate (thermodynamic product). These rearrangements occurred by a nucleophilic attack of the selenocyanate anion at two different carbon atoms of the seleniranium intermediate. The efficient regioselective synthesis of alkyl, allyl, 2-propynyl, benzyl, 4-fluorobenzyl, and 2-pyridinylmethyl 1,3-thiaselenol-2-ylmethyl selenides was developed based on the generation of sodium 1,3-thiaselenol-2-ylmethylselenolate from 1,3-thiaselenol-2-ylmethyl selenocyanate or bis(1,3-thiaselenol-2-ylmethyl) diselenide followed by nucleophilic substitution reactions. Sodium 1,3-thiaselenol-2-ylmethylselenolate underwent nucleophilic addition to alkyl propiolates in a regio- and stereoselective manner affording 1,3-thiaselenol-2-ylmethyl vinyl selenides in high yields predominantly with Z-configuration. Not a single representative of the 1,3-thiaselenol-2-ylmethyl selenide scaffold has been previously described in the literature.

One-Step Synthesis of Janus Fluorographene Derivatives

Fluorographene, a two-dimensional derivative of graphene, is an excellent starting material for the synthesis of graphene derivatives. In this work, a one-step, substrate-free method for the asymmetric functionalization of fluorographene layers with hydroxyl groups by a facile nucleophilic substitution reaction is reported. Such a chemical modification occurs in a biphasic aqueous-organic system under mild conditions, leading to Janus graphene nanosheets functionalized by hydroxyl groups on one side and retaining fluorine atoms on the other. The reported experimental route paves the way for two-dimensional bifacial graphene templates, thus broadening the application potential of graphene materials.