Iron(II)-Catalyzed Intramolecular Aminohydroxylation of Olefins with Functionalized Hydroxylamines

Selective N=S Coupling Reactions of N-Methoxy Arylamides and Sulfoxides Catalyzed by Iron Salt

An iron-catalyzed selective N=S coupling of N-methoxy amides and sulfoxides has been developed and was found to be a highly efficient method for the synthesis of N-acyl sulfoximines. Electron-donating as well as electron-withdrawing groups on the phenyl ring are tolerated, and even sensitive substituents are compatible. The current catalytic transformation was conducted under an air atmosphere and can be easily scaled up to a gram scale with a catalyst loading of only 1 mol %. In this case, both coupling partners are used in their native forms, thus obviating prior functionalization and activation.

Enhanced synthesis of chloramphenicol intermediate L-threo-p-nitrophenylserine using engineered L-threonine transaldolase and by-product elimination

L-threo-p-nitrophenylserine (component 2) is an important intermediate during synthesis of chloramphenicol. However, its biosynthesis is limited by enzyme activity and stereoselectivity. In this study, we achieved a breakthrough in the high-efficiency production of 2 by employing engineered Chitiniphilus shinanonensis L-threonine transaldolase (ChLTTA) in conjunction with a by-product elimination system within a one-pot reaction. Notably, a novel visual stepwise high-throughput screening method was developed for the directed evolution of ChLTTA, leveraging its characteristic color. The engineered mutant F70D/F59A (Mu6 variant) emerged as a star performer, exhibiting a remarkable 2.6-fold increase in catalytic efficiency over the wild-type ChLTTA, coupled with an outstanding 91.5 % diastereoisomer excess (de). Molecular dynamics (MD) simulations unraveled the mechanism responsible for the enhanced catalytic performance observed in the Mu6 variant. Meanwhile, the Mu6 variant was coupled with Saccharomyces cerevisiae ethanol dehydrogenase (ScADH) and Candida boidinii formate dehydrogenase (CbFDH) to create a high-efficiency cascade system (E.coli/pRSF-Mu6-ScADH-CbFDH). Under optimized conditions, this cascade system demonstrated unparalleled performance, yielding 201.5 mM of 2 with an impressive conversion of 95.9 % and a de value of 94.5 %. This achievement represents the highest reported yield to date. This study offers a novel insight into the sustainable and efficient production of chloramphenicol intermediate.

Visible-Light-Driven Iron-Catalyzed Intermolecular Benzylic C(sp3)-H Amination with 1,2,3,4-Tetrazoles

A visible-light-driven iron-catalyzed C(sp3)-H amination of diphenylmethane derivatives with 1,2,3,4-tetrazoles under mild conditions has been developed. The reaction proceeds with photosensitizer-free conditions and features satisfactory to good yields. Mechanistic studies revealed that the reaction proceeded via an iron-nitrene intermediate, and H atom abstraction was the rate-determining step. Computational studies showed that the denitrogenation of 1,2,3,4-tetrazole depends on the conversion of the sextet ground state of 1,2,3,4-tetrazole-bounding iron species to the quartet spin state under visible-light irradiation.

Intramolecular Carboxyamidation of Alkyne-Tethered O-Acylhydroxamates through Formation of Fe(III)-Nitrenoids

We developed intramolecular carboxyamidations of alkyne-tethered O-acylhydroxamates followed by either thermally induced spontaneous or 4-(dimethylamino)pyridine-catalyzed O→O or O→N acyl group migration. Under iron-catalyzed conditions, the carboxyamidation products were generated in high yield from both Z-alkene and arene-tethered substrates. DFT calculations indicate that the iron-catalyzed carboxyamidation proceeds via a stepwise mechanism involving iron-imidyl radical cyclization followed by intramolecular acyloxy transfer from the iron center to the alkenyl radical center to furnish the cis-carboxyamidation product. Upon treatment with 4-(dimethylamino)pyridine, the Z-alkene-tethered carboxyamidation products underwent selective O→O acyl migration to generate 2-acyloxy-5-acyl pyrroles. Thermal O→N acyl migration occurs during carboxyamidation if the Z-alkene linker contains an alkyl or an aryl substituent at the β-position of the carbonyl group. On the other hand, the arene linker-containing compounds selectively undergo O→N acyl migration to generate N-acyl-3-acylisoindolinones, and the corresponding O→O acyl migration forming isoindole derivatives was not observed.

Ligand-Promoted Iron-Catalyzed Nitrene Transfer for the Synthesis of Hydrazines and Triazanes through N-Amidation of Arylamines

Herein, we report that bulky alkylphosphines such as PtBu3 can switch the roles from actor to spectator ligands to promote the FeCl2 -catalyzed N-amidation reaction of arylamines with dioxazolones, giving hydrazides in high efficiency and chemoselectivity. Mechanistic studies indicated that the phosphine ligands could facilitate the decarboxylation of dioxazolones on the Fe center, and the hydrogen bonding interactions between the arylamines and the ligands on Fe nitrenoid intermediates might play a role in modulating the delicate interplay between the phosphine ligand, arylamine, and acyl nitrene N, favoring N-N coupling over N-P coupling. The new ligand-promoted N-amidation protocols offer a convenient way to access various challenging triazane compounds via double or sequential N-amidation of primary arylamines.

Ligand-Enabled Carboamidation of Unactivated Alkenes through Enhanced Organonickel Electrophilicity

Catalytic carboamination of alkenes is a powerful synthetic tool to access valuable amine scaffolds from abundant and readily available alkenes. Although a number of synthetic approaches have been developed to achieve the rapid buildup of molecular complexity in this realm, the installation of diverse carbon and nitrogen functionalities onto unactivated alkenes remains underdeveloped. Here we present a ligand design approach to enable nickel-catalyzed three-component carboamidation that is applicable to a wide range of alkenyl amine derivatives via a tandem process involving alkyl migratory insertion and inner-sphere metal-nitrenoid transfer. With this method, various nitrogen functionalities can be installed into both internal and terminal unactivated alkenes, leading to differentially substituted diamines that would otherwise be difficult to access. Mechanistic investigations reveal that the tailored Ni(cod)(BQiPr) precatalyst modulates the electronic properties of the presumed π-alkene-nickel intermediate via the quinone ligand, leading to enhanced carbonickelation efficiency across the unactivated C═C bond. These findings establish nickel's ability to catalyze multicomponent carboamidation with a high efficiency and exquisite selectivity.

Nitrene-Mediated Enantioselective Intramolecular Olefin Oxyamination to Access Chiral γ-Aminomethyl-γ-Lactones

Attaching a nitrene precursor to an intramolecular nucleophile allows for a catalytic asymmetric intramolecular oxyamination of alkenes in which the nucleophile adds in an endocyclic position and the amine in an exocyclic fashion. Using chiral-at-ruthenium catalysts, chiral γ-aminomethyl-γ-lactones containing a quaternary carbon in γ-position are provided in high yields (up to 99 %) and with excellent enantioselectivities (up to 99 % ee). DFT calculations support the possibility of both a singlet (concerted oxyamination of the alkene) and triplet pathway (stepwise oxyamination) for the formation of the predominant stereoisomer. γ-Aminomethyl-γ-lactones are versatile chiral building blocks and can be converted to other heterocycles such as δ-lactams, 2-oxazolidinones, and tetrahydrofurans.

Mechanistic Studies of Iron-PyBOX-Catalyzed Olefin Amino-Oxygenation with Functionalized Hydroxylamines

Iron-catalyzed amino-oxygenation of olefins often uses discrete ligands to increase reactivity and broaden substrate scope. This work is focused on examining ligand effects on reactivity and in situ iron speciation in a system which utilizes a bisoxazoline ligand. Freeze-trapped ⁵⁷Fe Mössbauer and EPR spectroscopies as well as SC-XRD experiments were utilized to isolate and identify the species formed during the catalytic reaction of amino-oxygenation of olefins with functionalized hydroxylamines, as well as in the precatalytic mixture of iron salt and ligand. Experiments revealed significant influence of ligand and solvent on the speciation in the precatalytic mixture which led to the formation of different species which had significant influence on the reactivity. In situ experiments showed no evidence for the formation of an Fe(IV)-nitrene intermediate, and the isolation of a reactive intermediate was unsuccessful, suggesting that the use of the PyBOX ligand led to the formation of more reactive intermediates than observed in the previously studied system, preventing direct detection of intermediate species. However, isolation of the seven coordinate Fe(III) species with three carboxylate units of the hydroxylamine and spin-trap EPR experiments suggest formation of a species with unpaired electron density on the hydroxylamine nitrogen, which is in accordance with formation of a potential iron iminyl radical species, as recently proposed in literature. An observed increase in yield when substrates devoid of C-H bonds as well as isolation of a ring-closed dead-end species with substrates containing these bonds suggests the identity of the functionalized hydroxylamine can dictate the reactivity observed in these reactions.

Iron-Catalyzed Intermolecular Oxyamination of Terminal Alkenes Promoted by HFIP Using Hydroxylamine Derivatives

An atom-economical intermolecular iron-catalyzed oxyamination of alkenes is described herein. The insertion of oxygenated and nitrogenated moieties from the hydroxylamine substrate was observed with full regio- and chemo-selectivity for terminal alkenes in good yields. HFIP as a solvent appeared to have a synergistic effect with the iron catalyst to promote the formation of the oxyaminated products. Preliminary mechanistic studies suggest a pathway going through an aziridination reaction followed by an in situ ring opening.

Nitrene transfer reaction with hydroxylamine derivatives

Recent progress on catalytic nitrene transfer reactions with hydroxylamine derivatives as prevalent precursors is summarized in this highlight. The salient features of these N-O derived nitrene transfer reagents are that they are readily available, bench-stable, and can be facilely activated by a range of transition metal-catalysts under mild conditions. The application of these reagents in transition metal-catalysis has led to many new amidation or amination reactions, such as C-H insertions and aziridination of olefins. These reagents have also been applied in difunctionalisation of unsaturated bonds, dearomative amination of indoles, and formation of N-X bonds. Moreover, the recent achievements in photocatalysis and enzyme catalysis further emphasize the importance of these appealing reagents. This highlight provides an overview of these reactions reported in recent years. Challenges and potential opportunities for future developments are also discussed.

Cycloisomerization of Alkyne-Tethered N-Acyloxycarbamates to 2-(3H)Oxazolones through Nitrenoid-Mediated Carboxyamidation

The cycloisomerization of alkyne-tethered N-benzoyloxycarbamates to 2-(3H)oxazolones is described. Two catalytic systems are tailored for intramolecular 5-exo-alkyne carboxyamidation and concomitant alkene isomerization. PtCl₂ /CO (5 mol%, toluene, 100 °C) promotes both carboxyamidation and alkene isomerization but has a limited substrate scope. On the other hand, FeCl₃ (5 mol%, CH₃ CN, 100 °C) promotes carboxyamidation effectively but a cocatalyst is required for the exocyclic alkene isomerization. Thus, a two-step one-pot protocol has been developed for a broader reaction scope, which involves FeCl₃ -catalyzed carboxyamidation and base-induced alkene isomerization. Crossover experiments suggest that these reactions proceed mainly through a mechanism involving acylnitrenoid intermediates rather than carbenoid intermediates.

Regiodivergent Electrophotocatalytic Aminooxygenation of Aryl Olefins

A method for the regiodivergent aminooxygenation of aryl olefins under electrophotocatalytic conditions is described. The procedure employs a trisaminocyclopropenium (TAC) ion catalyst with visible light irradiation under a controlled electrochemical potential to convert aryl olefins to the corresponding oxazolines with high chemo- and diastereoselectivity. With the judicious choice between two inexpensive and abundant reagents, namely water and urethane, either 2-amino-1-ol or 1-amino-2-ol derivatives could be prepared from the same substrate. This method is amenable to multigram synthesis of the oxazoline products with low catalyst loadings.

The advent of electrophilic hydroxylamine-derived reagents for the direct preparation of unprotected amines

Electrophilic aminating reagents have seen a renaissance in recent years as effective nitrogen sources for the synthesis of unprotected amino functionalities. Based on their reactivity, several noble and non-noble transition metal catalysed amination reactions have been developed. These include the aziridination and difunctionalisation of alkenes, the amination of arenes as well as the synthesis of aminated sulfur compounds. In particular, the use of hydroxylamine-derived (N-O) reagents, such as PONT (PivONH3OTf), has enabled the introduction of unprotected amino groups on various different feedstock compounds, such as alkenes, arenes and thiols. This strategy obviates undesired protecting-group manipulations and thus improves step efficiency and atom economy. Overall, this feature article gives a recent update on several reactions that have been unlocked by employing versatile hydroxylamine-derived aminating reagents, which facilitate the generation of unprotected primary, secondary and tertiary amino groups.

Iron(II)-Catalyzed Nitrene Transfer Reaction of Sulfoxides with N-Acyloxyamides

An iron(II)-catalyzed nitrene transfer reaction of sulfoxides with N-acyloxyamides has been developed, leading to the efficient construction of N-acyl sulfoximines with high functional-group compatibility. The current catalytic transformation was carried out under an air atmosphere at ambient temperature and could be scaled up to gram scale with a catalyst loading of 1 mol %. Application of the methodology was demonstrated by facile C-H acetoxylation and olefination using the N-acyl sulfoximine as the directing group.

Photoredox/Iron Dual-Catalyzed Insertion of Acyl Nitrenes into C-H Bonds

In this work, the use of N-acyloxybenzamides as efficient acyl nitrene precursors under photoredox/iron dual catalysis is reported. The resulting acyl nitrenes could be captured by various types of C-H bonds and S- or P-containing molecules. Mechanism investigations suggested that the formation of the acyl nitrene from the N-acyloxybenzamide occurs by a photoredox process, and it is believed that in this redox process oxidative N-H bond cleavage of the N-acyloxybenzamide occurs prior to reductive N-O bond cleavage of the N-acyloxybenzamide.

Construction of N-Acyliminophosphoranes via Iron(II)-Catalyzed Imidization of Phosphines with N-Acyloxyamides

Employing FeCl₂ as a cheap and readily available catalyst, a facile imidization of phosphines with N-acyloxyamides is described, affording synthetically useful N-acyliminophosphoranes with high functional group tolerance. The transformation is easily performed under an air atmosphere at room temperature and could be scaled up to gram scale with a catalyst loading of 1 mol %. The iminophosphoranyl moiety in the product was further utilized as an effective directing group for controllable ortho C(sp²)-H bond amidations under Rh(III) catalysis.

A Combined Spectroscopic and Computational Study on the Mechanism of Iron-Catalyzed Aminofunctionalization of Olefins Using Hydroxylamine Derived N-O Reagent as the "Amino" Source and "Oxidant"

Herein, we study the mechanism of iron-catalyzed direct synthesis of unprotected aminoethers from olefins by a hydroxyl amine derived reagent using a wide range of analytical and spectroscopic techniques (Mössbauer, Electron Paramagnetic Resonance, Ultra-Violet Visible Spectroscopy, X-ray Absorption, Nuclear Resonance Vibrational Spectroscopy, and resonance Raman) along with high-level quantum chemical calculations. The hydroxyl amine derived triflic acid salt acts as the “oxidant” as well as “amino” group donor. It activates the high-spin Fe(II) (S_t = 2) catalyst [Fe(acac)₂(H₂O)₂] (1) to generate a high-spin (S_t = 5/2) intermediate (Int I), which decays to a second intermediate (Int II) with S_t = 2. The analysis of spectroscopic and computational data leads to the formulation of Int I as [Fe(III)(acac)₂-N-acyloxy] (an alkyl-peroxo-Fe(III) analogue). Furthermore, Int II is formed by N–O bond homolysis. However, it does not generate a high-valent Fe(IV)(NH) species (a Fe(IV)(O) analogue), but instead a high-spin Fe(III) center which is strongly antiferromagnetically coupled (J = −524 cm^–1) to an iminyl radical, [Fe(III)(acac)₂-NH·], giving S_t = 2. Though Fe(NH) complexes as isoelectronic surrogates to Fe(O) functionalities are known, detection of a high-spin Fe(III)-N-acyloxy intermediate (Int I), which undergoes N–O bond cleavage to generate the active iron–nitrogen intermediate (Int II), is unprecedented. Relative to Fe(IV)(O) centers, Int II features a weak elongated Fe–N bond which, together with the unpaired electron density along the Fe–N bond vector, helps to rationalize its propensity for N-transfer reactions onto styrenyl olefins, resulting in the overall formation of aminoethers. This study thus demonstrates the potential of utilizing the iron-coordinated nitrogen-centered radicals as powerful reactive intermediates in catalysis.

Access to β-Lactams via Iron-Catalyzed Olefin Oxyamidation Enabled by the π-Accepting Phthalocyanine Ligand

Herein, we report the development of an iron-catalyzed olefin oxyamidation by utilizing tethered dioxazolones as the nitrenoid precursor to produce valuable β-lactam scaffolds. Mechanistic studies revealed that a relatively strong π-accepting ability of the phthalocyanine ligand is critical in generating the key triplet iron-imidyl radical intermediate to enable the 4-exo-trig-lactamization with the incorporation of oxygen nucleophiles in high diastereoselectivity. This cyclization approach was readily extended to the highly efficient γ-lactam synthesis (TON > 300).

N-Aroyloxycarbamates as switchable nitrogen and oxygen precursor: Ir/Cu controlled divergent C–H functionalization of heteroarenes

Chemodivergent control in the functionalization of nitrogen-directed aromatic C–H bonds has been achieved by a switchable catalyst.

Iron-catalyzed domino coupling reactions of π-systems

The development of environmentally benign, inexpensive, and earth-abundant metal catalysts is desirable from both an ecological and economic standpoint. Certainly, in the past couple decades, iron has become a key player in the development of sustainable coupling chemistry and has become an indispensable tool in organic synthesis. Over the last ten years, organic chemistry has witnessed substantial improvements in efficient synthesis because of domino reactions. These protocols are more atom-economic, produce less waste, and demand less time compared to a classical stepwise reaction. Although iron-catalyzed domino reactions require a mindset that differs from the more routine noble-metal, homogenous iron catalysis they bear the chance to enable coupling reactions that rival that of noble-metal-catalysis. This review provides an overview of iron-catalyzed domino coupling reactions of π-systems. The classifications and reactivity paradigms examined should assist readers and provide guidance for the design of novel domino reactions.

Chiral Hypervalent Iodine Catalysis Enables an Unusual Regiodivergent Intermolecular Olefin Aminooxygenation

A novel iodide-catalyzed intermolecular aminooxygenation strategy is described here. Amide is used as the O- and N- source to probe for regiocontrol strategies. Notably, simple additives can be selectively introduced to achieve regiodivergent oxyamination processes for electronically activated alkenes while being regio-complementary for unactivated alkenes. Our preliminary data demonstrates that this regiocontrol strategy based on nucleophile can also be applied in asymmetric processes using chiral hypervalent iodine catalysis.

Iron-catalyzed stereoselective haloamidation of amide-tethered alkynes

In this work, by using N-methoxybenzamides as efficient acyl nitrene precursors, an iron-catalyzed formal cis-haloamidation of alkyne is reported. Without assistance of additives, the reaction worked well in the presence of 50 mol% FeCl3 or FeBr3, leading to a series of chloro/bromo-containing isoindolin-5-ones with high efficiency and wide reaction scope. In the reaction, the iron-facilitated haloamidation proceeds through a halo anion-participating concerted [3+2] cyclization to release the final products. The key intermediate ferric acyl nitrene A is generated in situ from a formal removal of MeOH.

Recent advances in aminative difunctionalization of alkenes

Alkenes are versatile building blocks in modern organic synthesis. In the difunctionalization reactions of alkenes, two functional groups can be simultaneously introduced into the π system. This is an efficient strategy for the synthesis of multifunctional compounds with complex structures and has the advantages of atom and step economy. Nitrogen-containing organic compounds are widely found in natural products and synthetic compounds, such as dyes, pesticides, medicines, artificial resins, and so on. Many natural products with high biological activity and a broad range of drugs have nitrogen-containing functional groups. The research on the construction methods of C-N bonds has always been one of the most important tasks in organic synthesis, especially in drug synthesis, and the synthetic methods starting from simple and easily available raw materials have been a topic of interest to chemists. The aminative difunctionalization of alkenes can efficiently construct C-N bonds, and at the same time, prepare some compounds that usually require multiple steps of reaction. It is one of the most effective strategies for the simple and efficient synthesis of functionalized nitrogen-containing compounds. This review outlines the major developments focusing on the transition metal-catalyzed or metal-free diamination, aminohalogenation, aminocarbonation, amino-oxidation and aminoboronation reactions of alkenes from 2015-2020.

Aminolactonization of Unactivated Alkenes Catalyzed by Aryl Iodine

A one-step protocol of the aryl iodine-catalyzed aminolactonization of unactivated alkenes under oxidation conditions was first reported to efficiently construct diverse amino lactones in a short time using HNTs₂ as the compatible nitrogen source. In addition, we investigated the influence of the reaction rate based on the structure of the iodoarene precatalyst, which revealed the selective adjustment effect on aminolactonization and oxylactonization. Finally, preliminary experiments verified the feasibility of asymmetric aminolactonization catalyzed by a chiral iodoarene precatalyst.

Nitrene-mediated intermolecular N-N coupling for efficient synthesis of hydrazides

N-N linkages are found in many natural compounds and endow fascinating structural and functional properties. In comparison to the myriad methods for the construction of C-N bonds, chemistry for N-N coupling, especially in an intermolecular fashion, remains underdeveloped. Here, we report a nitrene-mediated intermolecular N-N coupling of dioxazolones and arylamines under iridium or iron catalysis. These reactions offer a simple and efficient method for the synthesis of various hydrazides from readily available carboxylic acid and amine precursors. Although the Ir-catalysed conditions usually give higher N-N coupling yield than the Fe-catalysed conditions, the reactions of sterically more demanding dioxazolones derived from α-substituted carboxylic acids work much better under the Fe-catalysed conditions. Mechanistic studies revealed that the nitrogen atom of Ir acyl nitrene intermediates has strong electrophilicity and can undergo nucleophilic attack with arylamines with the assistance of Cl···HN hydrogen bonding to form the N-N bond with high efficiency and chemoselectivity.

Beyond osmium: progress in 1,2-amino oxygenation of alkenes, 1,3-dienes, alkynes, and allenes

Olefin 1,2-difunctionalization has emerged as a popular strategy within modern synthetic chemistry for the synthesis of vicinal amino alcohols and derivatives. The advantage of this approach is the single-step simplicity for rapid diversification, feedstock nature of the olefin starting materials, and the possible modularity of the components. Although there is a vast number of possible iterations of 1,2-olefin difunctionalization, 1,2-amino oxygenation is of particular interest due to the prevalence of both oxygen and nitrogen within pharmaceuticals, natural products, agrochemicals, and synthetic ligands. The Sharpless amino hydroxylation provided seminal results in this field and displayed the value in achieving methods of this nature. However, a vast number of new and novel methods have emerged in recent decades. This review provides a comprehensive review of modern advances in accomplishing 1,2-amino oxygenation of alkenes, 1,3-dienes, alkynes, and allenes that move beyond osmium to a range of other transition metals and more modern strategies such as electrochemical, photochemical, and biochemical reactivity.

Unravelling nitrene chemistry from acyclic precursors: recent advances and challenges

Recent advances in nitrene chemistry from acyclic precursors are reviewed in this paper.

Iron-catalyzed intramolecular acyl nitrene/alkyne metalation for the synthesis of pyrrolo[2,1-a]isoindol-5-ones

In this work, by using N-methoxybenzamides as efficient acyl nitrene precursors, an iron-catalyzed acyl nitrene/alkyne metalation is reported for the synthesis of pyrrolo[2,1-a]isoindol-5-ones.

Iodoarene-Catalyzed Oxyamination of Unactivated Alkenes to Synthesize 5-Imino-2-Tetrahydrofuranyl Methanamine Derivatives

Reported here is the room-temperature metal-free iodoarene-catalyzed oxyamination of unactivated alkenes. In this process, the alkenes are difunctionalized by the oxygen atom of the amide group and the nitrogen in an exogenous HNTs₂ molecule. This mild and open-air reaction provided an efficient synthesis to N-bistosyl-substituted 5-imino-2-tetrahydrofuranyl methanamine derivatives, which are important motifs in drug development and biological studies. Mechanistic study based on experiments and density functional theory calculations showed that this transformation proceeds via activation of the substrate alkene by an in situ generated cationic iodonium(III) intermediate, which is subsequently attacked by an oxygen atom (instead of nitrogen) of amides to form a five-membered ring intermediate. Finally, this intermediate undergoes an S_N2 reaction by NTs₂ as the nucleophile to give the oxygen and nitrogen difunctionalized 5-imino-2-tetrahydrofuranyl methanamine product. An asymmetric variant of the present alkene oxyamination using chiral iodoarenes as catalysts also gave promising results for some of the substrates.

Rhodium-catalyzed iminoiodane-mediated oxyamidation studies of 5-vinyluracil derivatives using aryl and alkyl sulfamates

The dirhodium tetraacetate-catalyzed iminoiodane-mediated reaction of 1,3-dimethyl-5-vinyluracil with phenyl sulfamate provided a high yield of 5-(1-acetyl-2-phenylsulfamoyl)ethyluracil via regioselective nucleophilic ring opening by acetate anion of the transiently formed 5-(1,2)-N-phenylsulfonylaziridine intermediate. This 1,2-oxyamidation reaction was found to be general for a variety of aryl- and alkylsulfamates as well as for various 1,3-dialkyl-5-vinyluracil derivatives. Addition of an alcohol to the reaction mixture allowed formation of the corresponding 1-alkoxy products. A selection of the substituted uracil derivatives prepared by this procedure was evaluated for cytotoxic activities in HCT-116 and HepG2 cancer cell lines and showed either no or modest activities. Further evaluation for α-glucosidase inhibition revealed that compounds 15ca and 15da were more active than acarbose, the reference inhibitor. This methodology thus allows efficient preparation of highly functionalized uracil derivatives thereby providing a synthetic route to novel compounds with potentially useful biological activities.

Photocatalytic Intramolecular C-H Amination Using N-Oxyureas as Nitrene Precursors

Nitrenes are remarkable high-energy chemical species that enable direct C-N bond formation, typically via controlled reactions of metal-stabilized nitrenes. Here, in contrast, the combined use of photocatalysis with careful engineering of the precursor enabled C-H amination forming imidazolidinones and related nitrogen heterocycles from readily accessible hydroxylamine precursors. Preliminary mechanistic results are consistent with the formation of free carbamoyl triplet nitrenes as reactive intermediates.

Oxyamination of Unactivated Alkenes with Electron-Rich Amines and Acids via a Catalytic Triiodide Intermediate

An aerobic catalytic oxidation process is described for the olefin oxyamination using acids and primary amines as the sources of O and N. Our mechanistic findings point to the formation of triiodide as a critical catalytic intermediate to account for the tolerance of electron-rich nucleophiles. This dual iodide and copper catalytic system is suitable for a formal [5+1] annulation process to access valuable lactam structures and highlighted by the synthesis of the pharmaceutical Zamifenacin.

Ligand-enabled gold-catalyzed 1,2-heteroarylation of alkenes

By adopting the interplay between ligand-enabled Au(i)/Au(iii) catalysis and the unique π-activation mode of gold complexes, a highly coveted 1,2-heteroarylation of alkenes has been accomplished.

Ruthenium porphyrin catalysed intermolecular amino-oxyarylation of alkenes to give primary amines via a ruthenium nitrido intermediate

Ruthenium porphyrin catalysed direct intermolecular amino-oxyarylation of alkenes including styrenes and 1,3-dienes to give primary amines with O-(2,4-dinitrophenyl)hydroxylamine as the amine source was achieved in moderate to good yields under mild reaction conditions. Spectroscopic analyses revealed that a ruthenium nitrido complex was the key reaction intermediate for the amino-oxyarylation reaction.

An enantioselective oxidative coupling reaction of 2-naphthol derivatives catalyzed by chiral diphosphine oxide-iron(ii) complexes

An enantioselective oxidative coupling of 2-naphthol derivatives is developed with the use of chiral Fe(ii)-diphosphine oxide complexes. Optically active 1,1-bi-2-naphthol derivatives can be synthesized in high yields when a 2 : 1 complex of (S)-xylyl-iPrO-BIPHEP-oxide and Fe(OTf)₂ is used in the presence of t-butyl hydroperoxide as an oxidant. The non-linear effect, X-ray crystal structure and ESI-MS suggest that a 2 : 1 complex of (S)-xylyl-iPrO-BIPHEP-oxide and Fe(OTf)₂ is a pre-catalyst for a Fe(iii)/Fe(iv) redox cycle.

Ligand Controlled Ir-Catalyzed Regiodivergent Oxyamination of Unactivated Alkenes

An intramolecular Ir(III)-catalyzed regiodivergent oxyamination of unactivated alkenes provides valuable γ-lactams, γ-lactones and δ-lactams. The regioselectivity is controlled by the electronically tunable cyclopentadienyl Ir(III)-complexes enabling oxyamination via either 5-exo or 6-endo pathways. With respect to the mechanism, we propose a highly reactive [3.1.0] bicycle intermediate derived from Ir(V) nitrene-mediated aziridination to be a key intermediate toward the synthesis of γ-lactams.