Tishchenko reactions of aldehydes promoted by diisobutylaluminum hydride and its application to the macrocyclic lactone formation

Aliphatic aldehydes react with catalytic amount of Dibal-H in n-pentane to give the corresponding Tishchenko products in good to excellent yields. On contrary, α-silyloxy aldehydes give α-silyloxy ketones via Oppenauer oxidation under similar condition. Tishchenko reaction of ω-alkene aldehydes followed by RCM and hydrogenation affords a convenient method to prepare the 11-37 membered macrocyclic lactones.     

Oxazolidinone/enamine ratios in the reactions of α-silyloxy and α-alkoxy aldehydes with proline

α-Silyloxy and α-alkoxy aldehydes (propanal derivatives 1–4), when treated with proline in DMSO-d₆, give oxazolidinones rather than enamines. In fact, the relative trend is much stronger than that of all other carbonyl compounds examined, including simple aldehydes, α-branched aldehydes, α-(alkylthio)aldehydes, and standard ketones. For 1–4, the high prevalence of oxazolidinones prevents or delays the partial racemization of the α-stereocenters.     

Bu4NI-catalyzed α-acyloxylation reaction of ethers and ketones with aldehydes and tert-butyl hydroperoxide

The reaction of (hetero)aromatic aldehydes or cinnamaldehyde with di-/multi-ethers in the presence of Bu₄NI and tert-butyl hydroperoxide generated corresponding α-acyloxy ethers. Reactions between (hetero)aromatic aldehydes or cyclohexanecarbaldehyde with arylalkyl ketones under similar conditions resulted in α-acyloxy ketones. Collectively, Bu₄NI-catalyzed α-acyloxylation reactions exhibit a broad scope of substrates and a high compatibility with functional groups.     

Selective Propargylation of Carbonyl Compounds and Imines with Barium Reagents

A Barbier‐type regioselective propargylation of aldehydes and ketones with (3‐bromobut‐1‐ynyl)trimethylsilane has been achieved using reactive barium as a low‐valent metal in THF. Especially in the case of ketones, the corresponding homopropargylic alcohols form almost exclusively. In the reaction of α,β‐unsaturated carbonyl compounds, only 1,2‐adducts have been observed. This method is also applicable to propargylation of imines, and the corresponding homopropargylic amines are obtained regiospecifically in good yields with diastereomeric ratios of up to 87:13.     

A novel synthesis of 1,2,4-oxadiazoles and isoxazoles

A novel synthesis of 1,2,4-oxadiazoles and isoxazoles is described by utilizing the reactions between amidoximes and α,β-alkynic aldehydes and/or ketones. Conjugate addition products, obtained from amidoximes and α,β-alkynic aldehydes and/or ketones, afford 1,2,4-oxadiazoles and isoxazoles when treated with bases and acids, respectively. 1,2,4-Oxadiazoles can also be synthesized directly from amidoximes and α,β-alkynic aldehydes in a one-pot manner under basic conditions. The reactions are general for a variety of starting compounds and tolerate the presence of aryl, heteroaryl and alkyl groups.     

Stereoretentive Addition of N‐tert‐Butylsulfonyl‐α‐Amido Silanes to Aldehydes,Ketones, α,β‐Unsaturated Esters,and Imines

Enantioenriched N‐tert‐butylsulfonyl‐α‐amido silanes were successfully reacted with aldehydes, ketones, imines, and α,β‐unsaturated esters in the presence of a sub‐stoichiometric amount of CsF (0.5 equiv) in 1,2‐dimethoxyethane (DME) at ?20 °C to afford the corresponding coupling products with up to 89 % enantiospecificity in a retentive manner.     

A Novel Synthesis of α-Tellanyl α,β-Unsaturated Aldehydes Using α-Tellanyl β-Alkoxyalkenyl Lithiums

Abstract

β-Ethoxy-α-phenyltellanylvinyl lithiums were successfully generated in situ from phenyltellanylacetaldehyde diethyl acetal with lithium 2,2,6,6-tetrame-thylpiperidide (LTMP) and underwent methylation or nucleophilic addition with aldehydes and ketones. The successive dehydration of the allylic alcohols with trimethylsilyl trifluoromethanesulfonate (TMSOTf) gave α-phenyltellanyl α,β-unsaturated aldehydes, which transformed to some useful compounds.     

Synthesis of Quinolines via a Metal‐Catalyzed Dehydrogenative N‐Heterocyclization

Efficient ruthenium‐, rhodium‐, palladium‐, copper‐ and iridium‐catalysed methodologies have been recently developed for the synthesis of quinolines by the reaction of 2‐aminobenzyl alcohols with carbonyl compounds (aldehydes and ketones) or the related alcohols. The reaction is assumed to proceed via a sequence involving initial metal‐catalysed oxidation of 2‐aminobenzyl alcohols to the related 2‐aminobenzaldehydes, followed by cross aldol reaction with a carbonyl compound under basic conditions to afford α,β‐unsaturated carbonyl compounds. These aldehydes or ketones can be also generated in situ via dehydrogenation of the related primary and secondary alcohols. In the final step cyclodehydration of the α,β‐unsaturated carbonyl compound intermediates gives quinolines. Good yields of quinolines were also obtained by reacting 2‐nitrobenzyl alcohols and secondary alcohols in the presence of a ruthenium catalyst. Finally, aniline derivatives afforded also a useful access to quinolines by the reaction with 1,3‐propanediol or 3‐amino‐1‐propanol, or in a three‐component reaction with benzyl alcohol and aliphatic alcohols.     

A Mild Oxidant for the Regeneration of Carbonyl Compounds from Oximes in Nonaqueous Condition

Since oximes have been empolyed as ketone or aldehyde functional group equivalents in synthetic organic chemistry, the conversion of oximes into their corresponding carbonyl compounds has received considerable attention. The classical method for the cleavage of oximes to parent aldehydes and ketones is hydrolysis in acid, which is not suitable for acid sensitive compounds1-2. In recent years, cleavage of oximes with ozone3, nitrogen tetraoxide4, copper chloride5 and bromine6 have been develope…     

Stereoselective hydrosilylation of enals and enones catalysed by palladium nanoparticles

A highly versatile and efficient hydrosilylation method by palladium nanoparticle catalysis allows the direct and chemoselective synthesis of 1) enolsilanes of high isomeric purity, 2) saturated aldehydes or ketones, or 3) the corresponding saturated acetals from α,β-unsaturated aldehydes or ketones. The choice of the product is determined by simply switching the solvent from THF to mixtures of THF/water or THF/alcohol.     

Triphenylmethylphosphonium Dichromate: An Effective and Chemoselective Reagent for Oxidation of Benzylic Alcohols to the Corresponding Aldehydes and Ketones

An efficient and straightforward method for oxidation of the benzylic alcohols to the corresponding aldehydes and ketones has been accomplished using triphenylmethylphosphonium dichromate (MTPPD) under solvent-free conditions with high chemoselectivity. The reaction is fast with good yields and straightforward workup.     

Study on the stannous halides promoted addition of 1,1,1-trichloro-2,2,2-trifluoroethane to aldehydes and the chemical transformation thereof

Promoted by stannous salts, 1,1,1-trichloro-2,2,2-trifluoroethane reacts readily with aliphatic, aromatic, and α, β-unsaturated aldehydes giving the corresponding alcohols bearing a CF3CCl2-moiety in good to excellent yields. These alcohols are farther oxidized by Jones reagent giving the corresponding ketones in high yields.     

Preparation and reactivity of phenyltelluroalkylphosphine oxides. Vinylic tellurides

Phenyltelluromethyldiphenylphosphine oxide was prepared by the reaction of methyldiphenylphosphine oxide with base and PhTeBr. The telluromethylphosphine oxide reacts with aldehydes and ketones to give the corresponding vinylic tellurides, with preferential E stereochemistry for aryl aldehydes and Z for alkyl aldehydes.     

Oxone/Sodium Chloride: A Simple and Efficient Catalytic System for the Oxidation of Alcohols to Symmetric Esters and Ketones

An efficient method for the oxidation of alcohols is presented. The use of catalytic amounts of sodium chloride in combination with oxone allows the conversion primary aliphatic alcohols to symmetric esters. Secondary alcohols can be easily oxidized to ketones, and benzylic alcohols are converted to the corresponding aldehydes. The method is cost effective and enviromentally benign.     

Computational insight into asymmetric uranyl‐salophen coordinated with α, β‐unsaturated aldehydes and ketones

The study of the catalytic activity and activation mechanism of asymmetric uranyl‐salophens with α, β‐unsaturated aldehydes or α, β‐unsaturated ketones, is a research hotspot. In this paper, the complexes of the uranyl–salophen(U‐S) modified by unilateral benzene, coordinated with cyclohexenone, cyclopentenone and acrolein, were investigated using density functional theory calculations at the level of B3LYP/6‐311G(d, p) basis set. The results showed that the uranyl‐salophen(U‐S) weakened the large π bond between C = C and C = O of the α, β‐unsaturated aldehydes and ketones, making the unsaturated aldehydes and ketones activated. In addition, the molecular‐recognition selectivity of the asymmetrical uranyl‐salophen for cyclohexenone and cyclopentenone were much higher than for acrolein.     

Trifluoroethanol as a metal-free, homogeneous and recyclable medium for the efficient one-pot synthesis of α-amino nitriles and α-amino phosphonates

Trifluoroethanol is found to be an efficient and recyclable medium in promoting one-pot, three-component coupling reactions of aldehydes or ketones, amines and trimethylsilyl cyanide or trimethyl phosphite to afford the corresponding α-amino nitriles or α-amino phosphonates in high yields. This protocol does not require the use of an acid or base catalyst.     

A ruthenium-catalyzed one-pot method for α-alkylation of ketones with aldehydes

Ketones react with an array of aldehydes in dioxane at 80 °C in the presence of a catalytic amount of RuCl₂(PPh₃)₃ along with KOH to give the corresponding α-alkylated ketones in moderate to good yields. A reaction pathway involving base-catalyzed cross-aldol reaction between ketones and aldehydes to form α,β-unsaturated ketones and regioselective reduction of carbon-carbon double bond of α,β-unsaturated ketones is proposed for this catalytic process.     

1,4-syn-Asymmetric induction in the titanium-mediated aldol reactions of chiral methyl α-silyloxy ketones

Good levels of 1,4-syn asymmetric induction are obtained in the TiCl₄-mediated aldol reaction of methyl α-silyloxy ketones with achiral aldehydes. Such methodology represents a new approach to the substrate-controlled acetate aldol reaction, which can be useful to design more efficient syntheses of natural products.     

Lewis acid-catalyzed novel [3+2] cycloaddition of methylenecyclopropanes with activated aldehydes or ketones

Methylenecyclopropanes react with activated aldehydes or ketones in the presence of various Lewis acids to give the corresponding [3+2] cycloaddition products having tetrahydrofuran (THF) skeleton in good yields and in some cases with high stereoselectivity.     

Ultrasound‐Promoted Magnesium‐Ammonium Bromide–Mediated Pinacol Coupling of Aromatic Aldehydes and Ketones

Pinacol coupling of aromatic aldehydes and ketones by Mg powder in 0.1‐mol/L ammonium bromide aqueous solution can lead to the corresponding pinacols in 22–90% yields within 1–3 h at rt under ultrasound irradiation.