4-Dialkylaminopyridines as Highly Active Acylation Catalysts. [New synthetic method (25)]

Electron-rich pyridines with para-N-heterocyclic imine substituents: ligand properties and coordination to CO2, SO2, BCl3 and PdII complexes

Electron-rich pyridines with π donor groups at the para position play an important role as nucleophiles in organocatalysis, but their ligand properties and utilization in coordination chemistry have received little attention. Herein, we report the synthesis of two electron-rich pyridines 1 and 2 bearing N-heterocyclic imine groups at the para position and explore their coordination chemistry. Experimental and computational methods were used to assess the donor ability of the new pyridines showing that they are stronger donors than aminopyridines and guanidinyl pyridines, and that the nature of the N-heterocyclic backbone has a strong influence on the pyridine donor strength. Coordination compounds with Lewis acids including the CO2, SO2, BCl3 and PdII ions were synthesized and characterized. Despite the ambident character of the new pyridines, coordination preferentially occurs at the pyridine-N atom. Methyl transfer experiments reveal that 1 and 2 can act as demethylation reagents.

Reactivity and Steric Parameters from 2D to 3D Bulky Pyridines: Increasing Steric Demand at Nitrogen with Chiral Azatriptycenes

Sterically hindered pyridines embedded in a three-dimensional triptycene framework have been synthesized, and their resolution by chiral HPLC enabled access to unprecedented enantiopure pyridines exceeding the known steric limits. The design principles for new axially chiral pyridine derivatives are then described. To rationalize their associations with Lewis acids and transition metals, a comprehensive determination of the steric and electronic parameters for this new class of pyridines was performed. This led to the general parameterization of the steric parameters (percent buried volume %VBur, Tolman cone angle θ, and He8_steric descriptor) for a large set of two- and three-dimensional pyridine derivatives. These parameters are shown to describe quantitatively their interactions with carbon- and boron-centered Lewis acids and were used to predict the ΔG° of association with the prototypical B(C6F5)3 Lewis acid widely used in frustrated Lewis pair catalysis. This first parameterization of pyridine sterics is a fundamental basis for the future development of predictive reactivity models and for guiding new applications of bulky and chiral pyridines in organocatalysis, frustrated Lewis pairs, and transition-metal catalysis.

Synthesis and catalytic properties of palladium(II) complexes with P,π-chelating ferrocene phosphinoallyl ligands and their non-tethered analogues

Hybrid phosphines usually combine a phosphine moiety with another heteroatom secondary donor group in their structures while compounds equipped with hydrocarbyl π-donor moieties remain uncommon. This contribution reports the synthesis and structural characterization of the first P/π-allyl-chelating complexes that were obtained using the structurally flexible and redox-active ferrocene unit as the scaffold, viz. [PdCl(R2PfcCHCHCH2-η3:κP)] (1R; R = Ph and cyclohexyl (Cy); fc = ferrocene-1,1'-diyl). These compounds were synthesized from the respective phosphinoferrocene carboxaldehydes R2PfcCHO via reaction with vinylmagnesium bromide to generate 1-(phosphinoferrocenyl)allyl alcohols, which were subsequently acetylated. The resulting allyl acetates reacted smoothly with [Pd2(dba)3]/[Et3NH]Cl (dba = dibenzylideneacetone) to produce the target compounds. Complexes 1R and their nontethered analogues [PdCl(η3-C3H5)(FcPR2-κP)] (5R; Fc = ferrocenyl) were evaluated as pre-catalysts for the Pd-catalysed allylic amination of cinnamyl acetate with aliphatic amines and Suzuki-Miyaura-type cross-coupling of 4-tolylboronic acid with benzoyl chloride. In these reactions, better results were achieved with compounds 5R (particularly with 5Ph), presumably because they form more stable LPd(0)-type catalysts.

From Potential Prebiotic Synthons to Useful Chiral Scaffolds: A Synthetic and Structural Reinvestigation of 2-Amino-Aldononitriles

This paper explores and revisits in detail the formation and characterization of sugar-based aminonitriles, whose ultimate origin can be traced to the interaction of biomolecules with cyanide. Although the synthesis and spectroscopic data of 2-amino-aldononitriles were reported long ago, there are both contradictory and confusing results among the published data. We have now addressed this concern through an exhaustive structural elucidation of acylated 2-amino- and 2-alkyl(aryl)amino-2-deoxyaldonitriles using mass spectrometry and FT-IR, FT-Raman, and NMR spectroscopies. Several structures could be unambiguously determined through single-crystal X-ray diffraction, which allowed us to correct other misassignments. Moreover, this study unveils how steric and electronic effects influence the acylation outcome of the amino, (alkyl, aryl)amino, or acetamido group at C-2. The chirality at the latter, which was assigned tentatively through optical rotation correlation, and hence the preferential threo stereochemistry generated during the cyanohydrin synthesis of 2-amino-2-deoxy aldononitriles have now been established with confidence.

Hydrothermal Synthesis of Highly Crystalline Zwitterionic Vinylene-Linked Covalent Organic Frameworks with Exceptional Photocatalytic Properties

Ionic covalent organic frameworks (COFs) featuring both crystallinity and ionic characteristics have attracted tremendous attention in recent years. Compared with single anion- or cation-containing ionic COFs, zwitterionic COFs possess unique functionalities beyond single ionic COFs such as tunable charge density and superhydrophilic and highly ion-conductive characteristics, endowing them with huge potential in various applications. However, it remains a considerable challenge to directly synthesize robust, highly crystalline zwitterionic COFs from the original building blocks. Herein, we report a green hydrothermal synthesis strategy to prepare highly crystalline zwitterionic vinylene-linked COFs (ZVCOFs) from the predesigned zwitterionic building block by utilizing 4-dimethylaminopyridine (DMAP) as the high-efficiency catalyst for the first time. Detailed theoretical calculations and experiments revealed that both the high catalytic activity of DMAP and the unique role of water contributed to the formation of highly crystalline ZVCOFs. It was found that the participation of water could not only remarkably reduce the activation energy barrier and thus enhance the reaction reversibility but also enable the hydration of zwitterionic sites and facilitate ordered layered arrangement, which are favorable for the ZVCOF crystallization. Benefiting from the highly π-conjugated structure and hydrophilic characteristic, the obtained ZVCOFs achieved an ultrahigh sacrificial photocatalytic hydrogen evolution rate of 2052 μmol h-1 under visible light irradiation with an apparent quantum yield up to 47.1% at 420 nm, superior to nearly all COF-based photocatalysts ever reported. Moreover, the ZVCOFs could be deposited on a support as a photocatalytic film device, which demonstrated a remarkable photocatalytic performance of 402.1 mmol h-1 m-2 for hydrogen evolution.

Anion-Activated Bases and Nucleophiles Characterized by Photoelectron Spectroscopy

Negative ion photoelectron spectra at 20 K along with ab initio [CCSD(T)] and M06-2X density functional theory calculations are reported for a series of six basic and nucleophilic pyridine derivatives with an anionic substituent [i.e., 3- and 4-PyrBX3-, where X = F, 4-t-BuC6H4, 4-MeOC6H4, and 3,5-(MeO)2C6H3]. Vertical detachment energies (VDEs) of these charge-activated reagents span from 4.50-5.85 eV and are well reproduced by M06-2X/aug-cc-pVTZ and CCSD(T)/maug-cc-pVTZ computations. Surprisingly, the VDEs are found to correlate with the SN2 reactivity of the PPh4+ salts of the substituted pyridine anions with 1-iodooctane in dichloromethane. This provides an experimental measure of the nucleophilicity of these charge-activated anions, which represent a new class of chemical reagent.

Diiminium Nucleophile Adducts Are Stable and Convenient Strong Lewis Acids

Strong Lewis acids are essential tools for manifold chemical procedures, but their scalable deployment is limited by their costs and safety concerns. We report a scalable, convenient, and inexpensive synthesis of stable diiminium-based reagents with a Lewis acidic carbon centre. Coordination with pyridine donors stabilises these centres; the 2,2'-bipyridine adduct shows a chelation effect at carbon. Due to high fluoride, hydride, and oxide affinities, the diiminium pyridine adducts are promising soft and hard Lewis acids. They effectively produce acylpyridinium salts from carboxylates that can acylate amines to give amides and imides even from electronically intractable coupling partners.

Electrostatically Enhanced 3- and 4-Pyridyl Borate Salt Nucleophiles and Bases

A variety of electrostatically enhanced 3- and 4-pyridylborate salt catalysts are reported and show significant improvement over an activated noncharged neutral control compound. Their nucleophilicity in a stoichiometric SN2 reaction and catalytic performance in a urethane synthesis are evaluated along with three methods for rapidly evaluating the basicity of these species. That is, qualitative titrations in CH2Cl2 and CHCl3 were carried out, two separate solution-state IR studies in CCl4 and CDCl3 are reported, and the proton affinities of the anionic components of the salts were computed. Charge differences between the anion and its protonated zwitterionic conjugate acid are evaluated along with the highest occupied molecular orbitals of the anions in relationship to some of the surprising reactivity findings that were observed in the two kinetic studies.

Ionic Liquids for the Chemical Recycling of Polymeric Materials and Control of Their Solubility

Plastics are wonderful materials that have modernized our daily life; however, importance of effective recycling of plastics is gradually recognized widely. In this account, we describe our discovery of new and efficient methods for the chemical recycling of plastics using ionic liquids (ILs). Since the chemical recycling usually requires high temperature conditions to breakdown chemical bonds in polymeric materials, we thought that less-flammability and non-volatility of ionic liquids are the most suitable physical properties for this purpose. Ionic liquids successfully depolymerized polyamides and unsaturated polyesters smoothly and corresponding monomeric materials were obtained in good yields. To the best of our knowledge, this was the first use of Ionic liquids for such reactions. However, we encountered another difficult problem-separation. To solve the problem, we developed solubility-switchable ionic liquids, a new type of ionic liquids in which solubility is readily changed using the chemistry of protective groups. Conversion between hydrophilic and lipophilic forms was readily achieved using a simple chemical treatment under mild conditions, and the complete separation of products was achieved by liquid-liquid-extraction. The robustness of either form unlocks their wide use as reaction solvents.

Decarboxylative Enamide Synthesis from Carboxylic Acid and Alkenyl Isocyanate

Herein, we reported a protocol to access the enamide via employing carboxylic acid and alkenyl isocyanate as the precursors promoted by DMAP without involving any metal catalysts and dehydration reagents. This protocol is simple and practical and tolerates numerous functional groups. Considering the simplicity, the ready availability of both starting materials, and the significance of the enamides, we expect that this reaction will find broad application.

Progress toward Proteome-Wide Photo-Cross-Linking to Enable Residue-Level Visualization of Protein Structures and Networks In Vivo

Cross-linking mass spectrometry (XL-MS) is emerging as a method at the crossroads of structural and cellular biology, uniquely capable of identifying protein-protein interactions with residue-level resolution and on the proteome-wide scale. With the development of cross-linkers that can form linkages inside cells and easily cleave during fragmentation on the mass spectrometer (MS-cleavable cross-links), it has become increasingly facile to identify contacts between any two proteins in complex samples, including in live cells or tissues. Photo-cross-linkers possess the advantages of high temporal resolution and high reactivity, thereby engaging all residue-types (rather than just lysine); nevertheless, photo-cross-linkers have not enjoyed widespread use and are yet to be employed for proteome-wide studies because their products are challenging to identify. Here, we demonstrate the synthesis and application of two heterobifunctional photo-cross-linkers that feature diazirines and N-hydroxy-succinimidyl carbamate groups, the latter of which unveil doubly fissile MS-cleavable linkages upon acyl transfer to protein targets. Moreover, these cross-linkers demonstrate high water-solubility and cell-permeability. Using these compounds, we demonstrate the feasibility of proteome-wide photo-cross-linking in cellulo. These studies elucidate a small portion of Escherichia coli's interaction network, albeit with residue-level resolution. With further optimization, these methods will enable the detection of protein quinary interaction networks in their native environment at residue-level resolution, and we expect that they will prove useful toward the effort to explore the molecular sociology of the cell.

Controlled Formation of Porous 2D Lattices from C3 -symmetric Ph6 -Me-Tribenzotriquinacene-OAc3

The on-surface self-assembly of molecules to form holey nanographenes is a promising approach to control the properties of the resulting 2D lattice. Usually, planar molecules are utilized to prepare flat, structurally confined molecular layers, with only a few recent examples of warped precursors. However, control of the superstructures is limited thus far. Herein, we report the temperature-controlled self-assembly of a bowl-shaped, acetylated C₃ -symmetric hexaphenyltribenzotriquinacene derivative on Cu(111). Combining scanning tunneling microscopy (STM) and density functional theory (DFT) confirms the formation of highly differing arrangements starting with π-stacked bowl-to-bowl dimers at low coverage at room temperature via chiral honeycomb structures, an intermediate trigonal superstructure, followed by a fully carbon-based, flattened hexagonal superstructure formed by on-surface deacetylation, which is proposed as a precursor for holey graphene networks with unique defect structures.

Novel Strategies for Enantio- and Site-Selective Molecular Transformations

A strategy for symmetric synthesis based on dynamic chirality of enolates (memory of chirality) has been developed. Asymmetric alkylation, conjugate addition, aldol reaction, and arylation via C-N axially chiral enolate intermediates are described. Asymmetric alkylation and conjugate addition via C-O axially chiral enolate intermediates with a half-life of racemization as short as approx. 1 s. at -78 °C have been accomplished. Organocatalysts for asymmetric acylation and site-selective acylation have been developed. Kinetic resolution of racemic alcohols via remote asymmetric induction by the catalyst is shown. Catalyst-controlled site-selective acylation of carbohydrates and its application to total synthesis of natural glycoside are described. Chemo-selective monoacylation of diols and selective acylation of secondary alcohols with reversal of inherent reactivity are also discussed. Geometry-selective acylation of tetrasubstituted alkene diols is achieved, where acylation takes place independent from the steric environments of the substrates.

Imprinted Polymeric Nanoparticles as Artificial Enzymes for Ester Hydrolysis at Room Temperature and pH 7

Natural esterases hydrolyze esters under physiological pHs but chemists often have to use strongly acidic or basic conditions for the same hydrolysis. We report synthetic nanoparticle catalysts that hydrolyze nonactivated alkyl esters at room temperature and neutral pH, with enzyme-like catalytic mechanisms and exquisite substrate selectivity. Unlike natural enzymes that denature easily at elevated temperatures, the synthetic catalysts become more active at higher temperatures.

The practical acetylation of nucleosides using acetic anhydride/acetic acid as a reusable solvent

The highly practical acetylation of free nucleosides is achieved using acetic anhydride/acetic acid as a reusable solvent and acetylating regent. A series of nucleosides, including ribosyl, deoxyribosyl, arabinosyl, acyclic and pyranosyl, and many clinical drugs were acetylated efficiently, even on large scale (200 g).

A micro-flow rapid dual activation approach for urethane-protected α-amino acid N-carboxyanhydride synthesis

This study demonstrated the rapid dual activation (10 s, 20 °C) of a combination of an α-amino acid N-carboxyanhydride and alkyl chloroformate in the synthesis of a urethane-protected α-amino acid N-carboxyanhydride in a micro-flow reactor. The key to success was the combined use of two amines that activated both substrates with proper timing. Three amines, i-Pr₂NEt, Me₂NBn, or N-ethylmorpholine, were used with pyridine in accordance with the steric bulkiness of a side chain in the α-amino acid N-carboxyanhydride. A variety of 16 urethane-protected α-amino acid N-carboxyanhydrides were synthesized in high yields. The role of amines was investigated based on the measurement of the time-dependent (0.5 to 10 s) decrease of α-amino acid N-carboxyanhydrides and alkyl chloroformates in the presence of amines via flash mixing technology using a micro-flow reactor. It was suggested that the in situ generated acylpyridinium cation was highly active and less prone to causing undesired decomposition compared with the acylammonium cation examined in this study. Thus, even at a very low concentration, the acylpyridinium cation facilitated the desired coupling reaction.

An N-Trifluoromethylation/Cyclization Strategy for Accessing Diverse N-Trifluoromethyl Azoles from Nitriles and 1,3-Dipoles

N-Trifluoromethyl azoles are valuable targets in medicinal chemistry, but their synthesis is challenging. Classical preparation of N-CF₃ azoles relies on the functional group interconversions but suffers from tedious N-pre-functionalization and unfriendly agents. Introduction of the CF₃ onto the nitrogen of heterocycles provides a direct route to such motifs, but the N-trifluoromethylation remains underdeveloped. Reported here is an alternative and scalable cyclization strategy based on NCF₃ -containing synthons for constructing N-CF₃ azoles. The approach involves the N-trifluoromethylation of nitriles followed by a [3+2] cyclization between resulting N-CF₃ nitrilium derivatives and 1,3-dipoles. PhICF₃ Cl was an effective CF₃ source for the transformation. As a result, a generic platform is established to divergently synthesize N-trifluoromethylated tetrazoles, imidazoles, and 1,2,3-triazoles by using sodium azide, activated methylene isocyanides, and diazo compounds as dipoles.

An Approach to the Synthesis of Electron-Rich and Hindered Esters and Its Application to the Synthesis of Acteoside

Electron-rich esters are ubiquitously distributed in natural products and play a central role in bioactivities. Herein, we disclose an efficient, mild, and general esterification approach to the synthesis of these esters by employing gold(I)-catalyzed acylation reaction with alkyne-tethered mixed anhydrides and alcohols. This method can be applied to ester-bond formation in complex substrates and facilitates efficient synthesis of acteoside, which belongs to the family of phenylethanoid glycosides and possesses a broad range of bioactivities.

Site-selective and inducible acylation of thrombin using aptamer-catalyst conjugates

Two acyl-transfer catalysts were conjugated to thrombin-binding DNA aptamers to acylate thrombin. Modification occurred site-selectively on Lys (≫Ser) residues proximal to the respective aptamer-thrombin interface, was selective for thrombin in the presence of other proteins, and the activity of both DNA-catalysts could be controlled by an external trigger.

Enhancing catalytic activity of pyridines via para-iminophosphorano substituents

Four pyridines decorated with π-donating iminophosphorano substituents (R₃PN-) in the 4-position were assessed as acylation catalysts. These catalysts display high sensitivity to the groups at phosphorus, with activities that are well correlated to the corresponding Hammett-type substituent constants (σ_p⁺), and can achieve superior activity over the most active dialkylamino-substituted pyridines. Iminophosphorano-substituted pyridines represent an easily accessible, tunable, and highly active class of nucleophilic organocatalysts.

Synthesis and antimicrobial activity of 1H-1,2,3-triazole and carboxylate analogues of metronidazole

Herein, a series of novel 1H-1,2,3-triazole and carboxylate derivatives of metronidazole (5a-i and 7a-e) were synthesized and evaluated for their antimicrobial activity in vitro. All the newly synthesized compounds were characterized by ¹H NMR, ¹³C NMR, HRMS, and ¹⁹F NMR (5b, 5c and 5h) spectroscopy wherever applicable. The structures of compounds 3, 5c and 7b were unambiguously confirmed by single crystal X-ray analysis diffraction method. Single crystal X-ray structure analysis supported the formation of the metronidazole derivatives. The antimicrobial (antifungal and antibacterial) activity of the prepared compounds was studied. All compounds (except 2 and 3) showed a potent inhibition rate of fungal growth as compared to control and metronidazole. The synthetic compounds also showed higher bacterial growth inhibiting effects compared to the activity of the parent compound. Amongst the tested compounds 5b, 5c, 5e, 7b and 7e displayed excellent potent antimicrobial activity. The current study has demonstrated the usefulness of the 1H-1,2,3-triazole moiety in the metronidazole skeleton.

Site-Selective Molecular Transformation: Acylation of Hydroxy Groups and C-H Amination

Control of site selectivity is an exciting direction for synthetic organic chemistry owing to the possibility of selective modification of multifunctionalized molecules, ultimately including biomacromolecules. In this review, our recent research related to site selectivity in two types of transformation, namely, the acylation of hydroxy groups and C-H amination, is summarized. Regarding the acylation of hydroxy groups, catalyst-controlled site selectivity enables unconventional retrosynthetic analysis, leading to efficient syntheses of sugar-related natural and unnatural products. Regarding C-H amination, the discovery of unprecedented reaction sites in intermolecular amination mediated by dirhodium nitrenes is described. The findings of this research demonstrate the power of site-selective transformation in the synthesis of a particular class of compounds.

Green Chemistry Meets Asymmetric Organocatalysis: A Critical Overview on Catalysts Synthesis

Can green chemistry be the right reading key to let organocatalyst design take a step forward towards sustainable catalysis? What if the intriguing chemistry promoted by more engineered organocatalysts was carried on by using renewable and naturally occurring molecular scaffolds, or at least synthetic catalysts more respectful towards the principles of green chemistry? Within the frame of these questions, this Review will tackle the most commonly occurring organic chiral catalysts from the perspective of their synthesis rather than their employment in chemical methodologies or processes. A classification of the catalyst scaffolds based on their E factor will be provided, and the global E factor (EG factor) will be proposed as a new green chemistry metric to consider, also, the synthetic route to the catalyst within a given organocatalytic process.

Patterns and compound specific stable carbon isotope analysis (δ13 C) of capsaicinoids in Cayenne chilli fruits of different ripening stages

INTRODUCTION

Capsaicinoids are alkaloids of high pungency which are exclusively formed by fruits of the genus Capsicum. Capsaicinoid content and composition of Capsicum fruits are influenced by ripening.

OBJECTIVE

Determination of changes in content and pattern of individual capsaicinoids in chilli pods with fruit ripening. Compound specific stable carbon isotope analysis (δ¹³ C values (‰), CSIA) was used for a better understanding of capsaicinoid development during fruit ripening.

METHODOLOGY

Cayenne chillies (Capsicum annuum) were grown in a glasshouse and harvested from different plants at four ripening stages (unripe, semi-ripe, ripe, overripe). Nine capsaicinoids (one verified by synthesis) were quantified by gas chromatography with mass spectrometry (GC-MS). For CSIA, an acetylation method for derivatising capsaicinoids was developed.

RESULTS

Variations in the patterns of the nine capsaicinoids were not relatable to a distinct ripening stage and also total contents varied extensively from plant to plant. However, changes in total capsaicinoid concentrations were systematic. In almost all plants, maximum values were reached in unripe fruits, then decreased to semi-ripe samples and increased again in the following ripening process. Likewise, δ¹³ C values of individual capsaicinoids were always by ~2‰ heavier in unripe than in semi-ripe or ripe fruits. However, direction of changes in sum-δ¹³ C values (‰) (taking contributions of all capsaicinoids together) could not be explained by corresponding variations in capsaicinoid concentrations.

CONCLUSIONS

Both quantification and δ¹³ C values (‰) verified the presence of ripening-related changes in the capsaicinoid content which may be caused by simultaneously proceeding reactions like synthesis, storage and degradation of capsaicinoids.

Xyloglucan processing machinery in Xanthomonas pathogens and its role in the transcriptional activation of virulence factors

Xyloglucans are highly substituted and recalcitrant polysaccharides found in the primary cell walls of vascular plants, acting as a barrier against pathogens. Here, we reveal that the diverse and economically relevant Xanthomonas bacteria are endowed with a xyloglucan depolymerization machinery that is linked to pathogenesis. Using the citrus canker pathogen as a model organism, we show that this system encompasses distinctive glycoside hydrolases, a modular xyloglucan acetylesterase and specific membrane transporters, demonstrating that plant-associated bacteria employ distinct molecular strategies from commensal gut bacteria to cope with xyloglucans. Notably, the sugars released by this system elicit the expression of several key virulence factors, including the type III secretion system, a membrane-embedded apparatus to deliver effector proteins into the host cells. Together, these findings shed light on the molecular mechanisms underpinning the intricate enzymatic machinery of Xanthomonas to depolymerize xyloglucans and uncover a role for this system in signaling pathways driving pathogenesis.

Debottlenecking a Pulp Mill by Producing Biofuels from Black Liquor in Three Steps

By extracting lignin, pulp production can be increased without heavy investments in a new recovery boiler, the typical bottleneck of a pulp mill. The extraction is performed by using 0.20 and 0.15 weight equivalents of CO2 and H2 SO4 respectively. Herein, we describe lignin esterification with fatty acids using benign reagents to generate a lignin ester mixable with gas oils. The esterification is accomplished by activating the fatty acid and lignin with acetic anhydride which can be regenerated from the acetic acid recycled in this reaction. The resulting mass balance ratio is fatty acid/lignin/acetic acid (2 : 1 : 0.1). This lignin ester can be hydroprocessed to generate hydrocarbons in gasoline, aviation, and diesel range. A 300-hour continuous production of fuel was accomplished. By recirculating reagents from both the esterification step and applying a water gas shift reaction on off-gases from the hydroprocessing, a favorable overall mass balance is realized.

Experimental observations on the reductive cleavage of endo and exo 3,4-O-benzylidene fucopyranoside derivatives

Reductive cleavage of methyl 3,4-O-benzylidene-α-L-fucopyranosides with BH₃·THF-TfOH and NaCNBH₃-TfOH systems resulted in enhanced reaction rates and selectivity compared to BH₃·THF-Bu₂BOTf. With this latter system, the nature of the O-2 substituent exerted a clear control on the reactivity but practically did not affect the regioselectivity. With TfOH the direction of cleavage was determined, as expected, by the configuration of the acetal carbon atom, but slightly influenced by its competitive epimerization. Protic conditions provided higher regioselectivity in the openings of the exo isomers, affording a useful approach to the practical synthesis of 3-O-benzyl ethers.

Selective Acetylation of Non-anomeric Groups of per-O-Trimethylsilylated Sugars

Selective modification of the hydroxyl groups of sugars has been a long-standing challenge due to their proximate relative reactivity. Herein, we report a TMSOTf-catalyzed selective acetylation of the non-anomeric hydroxyl groups of several per-O-TMS-protected sugar substrates while leaving their anomeric group unaffected. In addition to standing versatile by itself, the anomeric O-TMS group left intact can be functionalized to afford key sugar precursors such as imidate donors, which could otherwise be synthesized via a stepwise anomeric deprotection-functionalization procedure.

Synthesis process optimization and field trials of insecticide candidate NKY-312

NKY-312 is a highly active insecticide candidate with a simple structure. In order to carry out field trials and toxicity tests, its scale preparation is urgently needed, but the final step of the original synthetic route is a low-yielding sulfonylation reaction that generates a high proportion of a bissulfonylated by-product, its foliar contact activities against bean aphid (80% at 100 mg/kg) is significantly lower than that of NKY-312 (100% at 5 mg/kg), and uses pyridine as the solvent. In this work, we developed a highly selective (4-dimethylaminopyridine)-catalyzed monosulfonylation reaction that avoids the use of pyridine as a solvent and shows a much higher yield (98% yield with 98% HPLC purity) than the original reaction (68%). Then, we carried out the field trials and toxicity tests. In field experiments, the activities of NKY-312 against rice planthopper and wheat aphid were equal to pymetrozine and imidacloprid respectively.

Weakly Ionically Bound Thermosensitive Hyperbranched Polymers

We synthesized novel amphiphilic hyperbranched polymers (HBPs) with variable contents of weakly ionically tethered thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) macrocations in contrast to traditional covalent linking. Their assembling behavior was studied below and above the lower critical solution temperature (LCST). The HBPs underwent a morphological transition under changing temperature and ionic strength due to the LCST transition of PNIPAM and the reduction in the ionization degree of terminal ionic groups, respectively. We suggest that, in contrast to traditional branched polymers, ionically linked PNIPAM macrocations can reversibly disassociate from the sulfonate groups and form mobile coronas, endowing the dynamic micellar morphologies. In addition, assembly at the air-water interface confined PNIPAM macrocations and resulted in the formation of heterogeneous Langmuir-Blodgett (LB) monolayers with diverse surface morphologies for different peripheral compositions with circular domains formed in the condensed state. The HBPs with 25% PNIPAM showed larger and more stable circular domains that were partially preserved at high compression than those of HBPs with 50% PNIPAM. Moreover, the LB monolayers showed variable surface mechanical and surface charge distribution, which can be attributed to net dipole redistribution caused by the behavior of mobile PNIPAM macrocations and core sulfonate groups.

Strain-Induced Nucleophilic Ring Opening of Donor-Acceptor Cyclopropenes for Synthesis of Monosubstituted Succinic Acid Derivatives

1,2,3-Trisubstituted donor-acceptor cyclopropenes (DACPs) generated in situ from enoldiazo compounds react with nucleophiles to form α-substituted succinic acid derivatives in high yields. Initial dirhodium(II) carboxylate catalysis rapidly converts enoldiazo-acetates or -acetamides to DACPs that undergo catalyst-free Favorskii ring opening with amines, and also with anilines, alcohols, and thiols, when facilitated by catalytic amounts of 4-dimethylaminopyridine (DMAP). This methodology provides easy access to mixed esters and amides of monosubstituted succinic acids, including derivatives of naturally occurring compounds. It also affords dihydrazide, dihydroxamic acid, and diamide derivatives, as well as α-substituted tetrahydropyridazine-3,6-diones in high yields. Attempts to generate optically enriched DACPs were not successful because their populations having the R and S configurations formed with a chiral dirhodium catalyst are quite similar, and the loss of enantiocontrol likely originates from the DACP ring forming step which is reversible with its intermediate metal carbene.

Unusual temperature-sensitive protonation behaviour of 4-(dimethylamino)pyridine

An unusually strong impact of temperature on the protonation degree of DMAP in strong acid solutions has been found.

Development of a triazinedione-based dehydrative condensing reagent containing 4-(dimethylamino)pyridine as an acyl transfer catalyst

A new triazinedione-based reagent, (N,N'-dialkyl)triazinedione-4-(dimethylamino)pyridine (ATD-DMAP) was developed for the operationally simple dehydrative condensation of carboxylic acids. This reagent comprises an ATD core and DMAP as the leaving group, which is liberated into the reaction system to accelerate acyl transfer reactions. Upon adding ATD-DMAP to a mixture of carboxylic acids and alcohols in the presence of an amine base, the corresponding esters were formed rapidly at room temperature. Moreover, dehydrative condensation between carboxylic acids and amines using ATD-DMAP proceeded in high yield.