Making the Silylation of Alcohols Chiral: Asymmetric Protection of Hydroxy Groups

The non-enzymatic kinetic resolution of racemic mixtures of alcohols by silylation had been unknown before the turn of the century. This stands in stark contrast to established acylation techniques. The same applies to the related desymmetrization of diols. This might come as a surprise, given the significance of silyl ethers as protecting groups in multistep synthesis of complex molecules. The situation changed after a seminal report by Ishikawa nearly twenty years ago. Since then, enantioselective silylation of alcohols has matured and grown into an independent research field with organocatalytic and transition-metal-catalyzed approaches providing powerful solutions. This Minireview summarizes these recent advances with particular emphasis on the stereoselective dehydrogenative coupling of alcohols and hydrosilanes.     

Oxidation of Alcohols and Pyridines by a Water-Soluble Polyoxometalate with Hydrogen Peroxide

A water-soluble catalyst based on a silicotungstate polyoxometalate, K₈[β-SiW₁₁O₃₉] · 14H₂O, was developed for the oxidation of pyridines and alcohols with hydrogen peroxide. The reactions were carried out in water, and good yields of the corresponding heterocyclic N-oxides and ketones were obtained under relatively mild conditions. The catalyst could be easily recovered by extraction with ethyl acetate and reused several times.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Silylation of Hydroxy Groups with HMDS Under Microwave Irradiation and Solvent-Free Conditions

Phenols and alcohols are silylated with hexamethyldisilazane (HMDS) under microwave irradiation in solvent-free condition in good to excellent yields.     

钼、钨过氧配合物催化过氧化氢氧化烯烃和醇类反应的研究进展

综述了在钼、钨过氧配合物催化下，用清洁氧化剂对过氧化氢氧化醇类和烯烃 的最新研究进展。     

Quantitative Chirality and Concentration Sensing of Alcohols,Diols, Hydroxy Acids,Amines and Amino Alcohols using Chlorophosphite Sensors in a Relay Assay

Analytical methods that allow simultaneous determination of the concentration and enantiomeric composition of small sample amounts and are also compatible with high-throughput multi-well plate technology have received increasing attention in recent years. We now introduce a new class of broadly useful small-molecule probes and a relay sensing strategy that together accomplish these tasks with five classes of compounds including the challenging group of mono-alcohols—a scope that stands out among previously reported UV, fluorescence, and CD assays. Several chlorophosphite probes and aniline indicators have been evaluated and used for on-the-fly CD/UV sensing following a continuous workflow. The wide application range of the readily available sensors is highlighted with almost 30 alcohols, diols, hydroxy acids, amines and amino alcohols, and the accuracy of the stereochemical analysis is showcased with samples covering a wide range of concentrations and enantiomeric ratios.     

Direct Alkylation of Amines with Primary and Secondary Alcohols through Biocatalytic Hydrogen Borrowing

The reductive aminase from Aspergillus oryzae (Asp RedAm) was combined with a single alcohol dehydrogenase (either metagenomic ADH‐150, an ADH from Sphingobium yanoikuyae (SyADH), or a variant of the ADH from Thermoanaerobacter ethanolicus (Te SADH W110A)) in a redox‐neutral cascade for the biocatalytic alkylation of amines using primary and secondary alcohols. Aliphatic and aromatic secondary amines were obtained in up to 99 % conversion, as well as chiral amines directly from the racemic alcohol precursors in up to >97 % ee , releasing water as the only byproduct.     

钨酸钠与酸性离子液体催化醇的环境友好氧化反应

钨酸钠与酸性离子液体组成的催化体系可以催化双氧水进行醇的清洁氧化,反应在有机底物/水两相中进行.本体系在催化氧化仲醇为相应的酮时具有很好的活性;催化伯醇氧化时可以得到相应的醛、羧酸或两者的混合物.整个催化体系具有很好的重复利用性.     

Polycondensation of Sebacic Acid with Primary and Secondary Hydroxyl Groups Containing Diols Catalyzed by Candida antarctica Lipase B

Abstract

The aliphatic polyesters are normally synthesized by ester interchange reactions or direct esterification of hydroxyacids or diacid/diol combinations. Biotransformation, utilizing the enzymes as catalysts, was accepted as an alternative route for the synthesis of aliphatic polyesters and offers various advantages compared with the conventional, metal-catalyzed polymerization reactions. Previous studies indicated that lipase-catalyzed polycondensation reactions between diols and diacids occurred preferentially at primary hydroxyl groups of diols, when diols contained both primary and secondary hydroxyl groups. In this work, we investigated lipase-catalyzed polycondensation of diacids and secondary hydroxyl group–containing diols, and successfully synthesized polyesters by polycondensation with secondary hydroxyl groups as well as primary hydroxyl groups. Various diols, glycerol, 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, and 2,4-pentanediol were tested for the polycondensation. The polymerization was achieved by heating a mixture of lipase B, sebacic acid, and the diols in anhydrous toluene at 100 °C for 72 h. The resulting polymers were characterized by ¹H and ¹³C NMR spectroscopy, Fourier transform–infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography.     

Ruthenium‐Catalyzed Oxidation of Alkenes,Alkynes, and Alcohols to Organic Acids with Aqueous Hydrogen Peroxide

A protocol that adopts aqueous hydrogen peroxide as a terminal oxidant and [(Me₃tacn)(CF₃CO₂)₂Ru^III(OH₂)]CF₃CO₂ ( 1 ; Me₃tacn=1,4,7‐trimethyl‐1,4,7‐triazacyclononane) as a catalyst for oxidation of alkenes, alkynes, and alcohols to organic acids in over 80 % yield is presented. For the oxidation of cyclohexene to adipic acid, the loading of 1 can be lowered to 0.1 mol %. On the one‐mole scale, the oxidation of cyclohexene, cyclooctene, and 1‐octanol with 1 mol % of 1 produced adipic acid (124 g, 85 % yield), suberic acid (158 g, 91 % yield), and 1‐octanoic acid (129 g, 90 % yield), respectively. The oxidative C?C bond‐cleavage reaction proceeded through the formation of cis‐ and trans‐diol intermediates, which were further oxidized to carboxylic acids via C? C bond cleavage.     

Polyketide Building Blocks via Diastereoselective Nitrile Oxide Cycloadditions with Homoallylic Alcohols and Monoprotected Homoallylic Diols

A modular approach to Δ²‐isoxazolines, latent aldol adducts and polyketide building blocks, is reported. The magnesium‐mediated, hydroxyl‐directed method allows for the diastereoselective access to a wide variety of masked β‐hydroxy ketones, starting from readily available aliphatic and aromatic oximes, homoallylic alcohols and monoprotected homoallylic diols. The utility of the prepared Δ²‐isoxazolines as polyketide building blocks is demonstrated by their ready conversion into the corresponding β‐hydroxy ketones. The anti‐diastereoselectivity of the reaction was established by derivatization, NOE studies and comparison of known compounds. A rationale for the observed diastereoselectivity is proposed.     

微酸性条件下环己基过氧化氢分解制备环己酮工艺研究

针对传统碱性分解的不足,以有机铬酸酯为催化剂,对环己烷氧化液中的环己基过氧化氢分解制备环己酮工艺进行了探索,考察了在催化剂铬离子浓度150 ppm时,分解温度及时间对环己烷氧化液分解产物的影响,得出最佳的微酸性分解工艺条件。并在连续分解实验装置对前面得到的微酸性分解工艺条件进行验证。     

SnCl4催化丙酮与过氧化氢反应制取大环过氧化物

H₂O₂与过渡金属构成的催化体系可选择性地氧化烃类化合物,如芳烃的羟基化和烯烃的环氧化等^[1～3],且H₂O₂在应用中无环境污染,是一种颇有前途的氧化剂.有关金属催化H₂O₂与酮类化合物反应的报道很少.     

Reaction of Thiourea Dioxide and Hydrogen Peroxide with Coumarin

The system thiourea dioxide–hydrogen peroxide is found to effectively hydroxylate coumarin in aqueous solutions. The hydroxyl radical reacting with coumarin is shown to result from decomposition of the complex thiourea dioxide–H₂O₂. The obtained data are compared to the results of investigation of the reactions occurring in the system thiourea dioxide–H₂O₂ with terephthalic acid.