Regioselective Deoxygenation of the Cyclic Thionocarbonates of 2,3-Dihydroxy Esters with Magnesium in Methanol

Deoxygenation of the cyclic thionocarbonates of 2,3-dihydroxy esters was mediated with magnesium in methanol, which provided a facile method for the synthesis of α-hydroxy esters     

Asymmetric Synthesis of 2,3‐Disubstituted Cyclic Ketones by Enantioselective Conjugate Radical Additions

Enantioselective conjugate radical addition to 2‐acyloxymethyl cycloalkenones proceeds in high yield with outstanding diastereoselectivity and excellent enantioselectivity using chiral salen Lewis acids. The process provides access to 2,3‐disubstituted cycloalkanones, a structural motif present in natural products.     

Deoxygenation of Aldehydes and Ketones with Sodium Cyanoborohydride

Treatment of hydroxy-substituted aromatic aldehydes and ketones with sodium cyanoborohydride yields the corresponding methylene compounds under conditions which favor intermediate carbonium ion formation.     

Cyclopropanation Versus Deoxygenation in the Reactions of Halocarbenes with pre-Aromatic Ketones

Cyclopropanesareveryusefillintermediatesinorganicsynthesis'.OurpreviousstUdiesshowedthatthereactionsof2,4,6-triphenyIcycIoheptatrienonewithhaIcoarbenesgavealmostnocyclopropaneproduct'.Ontheotherhand.whenanotherpre-aromaticketoneIwasusedassubstrate,theonlyisolatedproductwasfoundtocontaincyclopropane(eq.I).Furthermore,whenthesubstratewastetraphenylcyclone(TPCP,2),bothcyclopropanationanddeoxygenationproductswereobtained(eq.2).Nowwewishtoreporttheserecentfindingsandelucidatethepossiblefactorsw…     

Reaction of Crossed Diperoxidation Between Cyclic Ketones and Alkyl Ketones

IntroductionThe thermal and photochemical decompositionof the diperoxides of cyclic ketones has been foundto provide a general method for the facile synthesisof macrocyclic compounds[1,2 ] .In addition,the useof diperoxides as initiators in polymerization hasbeen studied[3] .Forthose reasons,a better methodfor the synthesis of the requisite diperoxides isrequired.There are two different methods for thepreparation of the diperoxides. Griesbaum[4 ]obtained cyclopentanone diperoxide(yield 1 3 % …     

Enantioselective Reduction of Prochiral Ketones Using a Reagent Prepared from Lithium Aluminium Hydride, (+)Threo-1,16-Dibenzyloxy, 7(R),8(R)-Dihydroxy Hexadecane and Alcohol

Asymmetric reduction of prochiral ketones to optically active chiral secondary alcohols was achieved using a reagent prepared by modifying lithium aluminium hydride with a chiral auxiliary, (+)threo-1,16-dibenzyloxy,7,8-dihydroxy hexadecane and various additive alcohols. (+)threo-1,16-dibenzyloxy,7(R),8(R)-dihydroxy hexadecane was prepared from (+)threo-9(R),10(R),16-trihydroxy hexadecanoic acid. Alcohols such as CH₃(CH₂)_n-OH of different chain length (n = 0–11) and (R)-hydnocarpic alcohol were used. Complex prepared from (+)threo-1,16-dibenzyloxy,7(R),8(R)-dihydroxy hexadecane, LAH and (R)-hydnocarpic alcohol reduced acetophenone in moderate enantioselectivity (maximum of 70% ee). Various arylalkylketones were reduced with the same complex.     

Metal‐Free Deoxygenation of Carbohydrates

The conversion of readily available cellulosic biomass to valuable feedstocks and fuels is an attrative goal but a challenging transformation that requires the cleavage of multiple nonactivated C? O bonds. Herein, the Lewis acid trispentafluorophenylborane (B(C₆F₅)₃) is shown to catalyze the metal‐free hydrosilylative reduction of monosaccharides and polysaccharides to give hydrocarbons with reduced oxygen content. The choice of the silane reductant influences the degree of deoxygenation, with diethylsilane effecting the complete reduction to produce hexanes while tertiary silanes give partially deoxygenated tetraol and triol products.     

Reaction of Frustrated Lewis Pairs with Ketones and Esters

The frustrated Lewis pair (FLP) Mes₂PCH₂CH₂B(C₆F₅)₂ ( 1 ) reacts with an enolizable conjugated ynone by 1,4‐addition involving enolate tautomerization to give an eight‐membered zwitterionic heterocycle. The conjugated endione PhCO‐CH?CH‐COPh reacts with the intermolecular FLP tBu₃P/B(C₆F₅)₃ by a simple 1,4‐addition to an enone subunit. The same substrate undergoes a more complex reaction with the FLP 1 that involves internal acetal formation to give a heterobicyclic zwitterionic product. FLP 1 reacts with dimethyl maleate by selective overall addition to the C?C double bond to give a six‐membered heterocycle. It adds analogously to the triple bond of an acetylenic ester to give a similarly structured six‐membered heterocycle. The intermolecular FLP P(o‐tolyl)₃/B(C₆F₅)₃ reacts analogously with acetylenic ester by trans‐addition to the carbon–carbon triple bond. An excess of the intermolecular FLP tBu₃P/B(C₆F₅)₃, which contains a more nucleophilic phosphane, reacts differently with acetylenic ester examples, namely by O? C(alkyl) bond cleavage to give the {R‐CO₂[B(C₆F₅)₃]₂^?}[alkyl‐PtBu₃⁺] salts. Simple aryl or alkyl esters react analogously by using the borane‐stabilized carboxylates as good leaving groups. All essential products were characterized by X‐ray diffraction.     

Convenient Deoxygenation of Aromatic Ketones by Silica-Supported Chitosan Schiff Base Palladium Catalyst

Abstract

A novel and effective catalytic system, silica-supported chitosan Schiff base palladium complex (SiO₂–CS–Schiff base–Pd) was described for catalytic hydrogenation of aromatic ketones to corresponding hydrocarbons at ambient temperature and normal pressure of H₂.     

Method for Conversion of α-Ketols to Ketones. Deoxygenation with Iodotrimethylsilane

Iodotrimethylsilane has rapidly become a valuable reagent for organic synthesis since its use in the cleavage of alkyl esters and ethers^1,2,3 under essentially neutral conditions was introduced. For example, the conversion of ketals to ketones⁴, alcohols to iodides⁵, alkyl carbamates to amines, and sulfoxides to sulfides⁷ can now be readily promoted by iodotrimethylsilane.     

Thermodynamic and Kinetic Polymerizability of Cyclic Esters

Recent advances in the controlled ring-opening polymerization (ROP) of cyclic aliphatic esters are reviewed with a particular attention to thermodynamics and kinetics of the polymerization of industrially important monomers, namely: lactide (LA), 1,4-dioxan-2-one (DX), and ϵ-caprolactone (CL). For comparison, polymerization of β-lactones is discussed. Progress in stereocontrolled polymerization of monomers bearing centers of chirality [LA and β-butyrolactone (BL)] is also briefly reviewed.     

2，4-共轭不饱和酮、酯、腈的合成

前文我们报道了溴化对-苯基苯甲酰甲基二丁基碲、溴化对-溴苯甲酰甲基二丁基碲和溴化间-硝基苯甲酰甲基二丁基碲等碲盐与醛、酮缩合成α,β-不饱和酮的反应。为了进一步研究碲盐反应性能,扩大它在有机合成中应用范围,我们在前期工作基础上,由碲盐和(E)-α,β-不饱和醛合成了2,4-共轭不饱和酮、酯、腈,这是一种未见文献报道的新合成方     

Acylation of Unsaturated Halides,Alcohols, Esters and Ketones

treatment of the title compounds with acyl halide and Lewis acid affords unsaturated ketones (mainly α-β with aluminium chloride, selectively β-γ with silver tetrafluoroborate). Reduction of the alkenyl group gives polyfunctional ketones.     

Deoxygenation of Aromatic Ketones Using Transfer Hydrogenolysis with Raney Nickel in 2-Propanol

Aryl ketones are readily deoxygenated to their corresponding aryl alkanes upon treatment with Raney nickel catalyst in boiling 2-propanol.

Facile Protocol for Catalytic Frustrated Lewis Pair Hydrogenation and Reductive Deoxygenation of Ketones and Aldehydes

A series of ketones and aldehydes are reduced in toluene under H₂ in the presence of 5 mol % B(C₆F₅)₃ and either cyclodextrin or molecular sieves affording a facile metal‐free protocol for reduction to alcohols. Similar treatment of aryl ketones resulted in metal‐free deoxygenation yielding aromatic hydrocarbons.     

Oxidizable Ketones: Persistent Radical Cations from the Single‐Electron Oxidation of 2,3‐Diaminocyclopropenones.

Single electron oxidation of 2,3‐diaminocyclopropenones is shown to give rise to stable diaminocyclopropenium oxyl (DACO) radical cations. Cyclic voltammetry reveals reversible oxidations in the range of +0.70–1.10 V (vs. SCE). Computational, EPR, and X‐ray analysis support the view that the oxidized species is best described as a cyclopropenium ion with spin density located on the heteroatom substituents, including 23.5 % on oxygen. The metal–ligand behavior of the DACO radical is also described.     

Mild Deoxygenation of Aromatic Ketones and Aldehydes over Pd/C Using Polymethylhydrosiloxane as the Reducing Agent

Herein, a practical and mild method for the deoxygenation of a wide range of benzylic aldehydes and ketones is described, which utilizes heterogeneous Pd/C as the catalyst together with the green hydride source, polymethylhydrosiloxane. The developed catalytic protocol is scalable and robust, as exemplified by the deoxygenation of ethyl vanillin, which was performed on a 30 mmol scale in an open‐to‐air setup using only 0.085 mol % Pd/C catalyst to furnish the corresponding deoxygenated product in 93 % yield within 3 hours at room temperature. Furthermore, the Pd/C catalyst was shown to be recyclable up to 6 times without any observable decrease in efficiency and it exhibited low metal leaching under the reaction conditions.     

富电子杂环芳烃与酮酯的自由基脱氢偶联反应

报道了一种小分子酮、酯与富电子杂环芳烃的高度选择性的自由基脱氢交叉偶联反应. 酯、酮作为溶剂, 过氧化物加热条件下发生裂解与酯、酮作用产生α羰基碳中心自由基, 进而与富电子杂环芳烃发生交叉脱氢偶联, 得到一系列C-2官能化富电子杂环产物. 该反应成功地运用自由基的极性效应, 从而精确控制自由基反应的化学选择性. 此外, 该体系还具有反应迅速、操作简便、官能团兼容性较好、区域选择性单一等优点. 预期它将在合成有机化学上得到较广泛的应用.     

Oxidative Transformation of Functionalized Methyl Ketones into α-Ketocarboxylic Esters

Methyl ketones are oxidatively transformed into α-keto esters by metal ion assisted alcoholysis of the corresponding β-keto-α, α-dichloroalkyl sulfides.