A simple, user-friendly process for the homologation of aldehydes using tosylhydrazone salts

Aldehydes can be homologated to ketones in moderate to good yields using aryldiazomethanes generated in situ from tosylhydrazones. Chiral aldehydes can be employed with almost complete retention of configuration. The tosylhydrazones can also be generated in situ from the corresponding aldehyde leading to a one-pot process for coupling two different carbonyl compounds to give ketones.     

Reaction of arylsulfonylhydrazones of aldehydes with alpha-magnesio sulfones. A novel olefin synthesis

Reactions of representative tosylhydrazones of aldehydes and ketones with alpha-metalated sulfones were examined in order to develop a practical olefination method. Treatment of aldehyde tosylhydrazone 2 with an excess of alpha-lithiated methyl phenyl or dimethyl sulfones yielded 3a. The reaction of 2 with sterically unhindered lithiated alkyl sulfones gave mixtures of the respective olefination products 3b-d along with the Shapiro fragmentation product 4. Sterically hindered lithiated sulfones afforded Shapiro products exclusively. In contrast, aldehyde tosylhydrazones 2 or 6 in reactions with a variety of alpha-magnesio primary or secondary alkyl sulfones gave olefination products 3a-j and 7a-c in high yields (Tables 1 and 2). beta-Branched alkyl sulfones afforded predominantly (E)-alkenes, whereas unhindered primary sulfones gave mixtures of (E)- and (Z)-alkenes with low selectivity. Reaction of the 2,4,6-triisopropylbenzenesulfonylhydrazone (trisylhydrazone) of cyclodecanone 11c with alpha-magnesio methyl phenyl sulfone afforded the methylidene derivative 12a contaminated with the Shapiro product 13. Tosylhydrazone 2 resisted reaction with i-PrMgCl and gave only a small amount of the addition product in reaction with Bu(2)Mg. Some mechanistic aspects of the reaction of tosylhydrazones with organomagnesium compounds are discussed.     

The synthetic utility of amine borane reagents in the reduction of aldehydes and ketones

Primary and secondary amine boranes have been shown to be mild, efficient, and stereoselective reducing agents for aldehydes and ketones in protic or non-protic solvents with reactivity patterns different than diborane or sodium borohydride.     

Two-carbon homologation of aldehydes and ketones to α,β-unsaturated aldehydes

Phosphonate reagents were developed for the two-carbon homologation of aldehydes or ketones to unbranched- or methyl-branched α,β-unsaturated aldehydes. The phosphonate reagents, diethyl methylformyl-2-phosphonate dimethylhydrazone and diethyl ethylformyl-2-phosphonate dimethylhydrazone, contained a protected aldehyde group instead of the usual ester group. A homologation cycle entailed condensation of the reagent with the starting aldehyde, followed by removal of the dimethylhydrazone protective group with a biphasic mixture of 1 M HCl and petroleum ether. This robust two-step process worked with a variety of aldehydes and ketones. Overall isolated yields of unsaturated aldehyde products ranged from 71% to 86% after the condensation and deprotection steps.     

Preparation of aldehydes and ketones by oxidation of benzylic hydrocarbons with benzeneseleninic anhydride

Benzeneseleninic anhydride is a mild oxidant for the conversion of benzylic hydrocarbons into aldehydes or ketones.     

乙酸中碘催化氧化苄醇为相应醛或酮(英文)

本文报道了用I2/NaNO2/4-OH-TEMPO为催化剂,空气为氧化剂,在冰乙酸中催化氧化苄醇的方法.文中考察了催化剂各组分和温度对催化氧化反应的影响,在催化过程中碘替代过渡金属作为4-OH-TEMPO的共催化剂,在选择条件下苄醇氧反应的产物产率达到90%,在反应过程中生成醛或酮.     

Iodine-catalyzed N-alkylation of tosylhydrazones with benzylic alcohols

A new and highly efficient method for the C–N bond formation using molecular iodine-catalyzed N-alkylation reaction of tosylhydrazones with benzylic/benzhydryl alcohols at room temperature in methylene chloride is described. A variety of tosylhydrazones reacted readily with various substituted benzylic alcohols in presence of 20 mol % iodine under mild reaction conditions to produce the corresponding biologically active N-alkylated compounds in good to excellent yields.     

A Simple Method for Generation of Diazocompounds in an Aqueous Two-Phase System

Decomposition of tosylhydrazones of carbonyls in a basic medium is one of the most important methods for synthesis of diazocompounds (Bamford-Stevens reaction)¹. This reaction with arylaldehyde, arylalkyl- and diaryl ketone tosylhydrazones is usually carried out in the presence of sodium alkoxides in alcohols, glycols, their ethers or in pyridine. Diazocompounds stabilized by electron withdrawing groups can be generated under milder conditions (diluted aq NaOH solutions or basic Al₂O₃). The standard conditions of the Bamford-Stevens reaction are not suitable for the synthesis of diazoalkanes derived from aliphatic aldehydes and ketones.     

Silica gel promotes reductions of aldehydes and ketones by N-heterocyclic carbene boranes

N-Heterocyclic carbene boranes (NHC-boranes) such as 1,3-dimethylimidazol-2-ylidine trihydridoborane (diMe-Imd-BH(3)) serve as practical hydride donors for the reduction of aldehydes and ketones in the presence of silica gel. Primary and secondary alcohols are formed in good yields under ambient conditions. Aldehydes are selectively reduced in the presence of ketones. One, two, or even all three of the boron hydrides can be transferred. The process is attractive because all the components are stable and easy to handle and because both the reaction and isolation procedures are convenient.     

Organic reactions in a solid matrix-vi: Silica-gel supported reagents for the isolation of aldehydes and ketones

Semicarbazide-on silica gel and Girard-T-on-silica gel are described and evaluated as convenient reagents for efficient isolation of aldehydes and ketones from mixtures with other usual neutral organic components Semicarbazide-on-silica gel, which can be readily prepared, can effectively replace the classical Girard reagents, for the isolation of aldehydes and ketones in most cases.     

A novel,green 1-glycyl-3-methyl imidazolium chloride-copper(Ⅱ) complex catalyzed C-H oxidation of alkyl benzene and cyclohexane

A variety of alkyl-arenes and cyclohexane were converted to the corresponding ketones with NaCIO as the oxidant in the presence of l-glycyl-3-methyl imidazolium chloride-copper(Ⅱ) complex.This method contains simplified product isolation and catalyst recycling,affording benzylic C-H oxidation of alkyl-arenes imparting high yield of ketones.Furthermore,complex could be reused seven times without a significant loss of its catalytic activity.     

Pd(0)‐Catalyzed Tandem One‐Pot Reaction of Biphenyl Ketones/Aldehydes to the Corresponding Di‐substituted Aryl Olefins

Synthesis of di‐substituted aryl olefins via a Pd(0)‐catalyzed cross‐coupling reaction of biphenyl ketones/aldehydes, tosylhydrazide, and aryl bromides (or benzyl halides) was developed. This methodology was achieved by one‐pot two‐step reactions involving the preparation of N ‐tosylhydrazones by reacting tosylhydrazide with biphenyl ketones/aldehydes, followed by coupling with aryl bromides (or benzyl halides) in the presence of Pd(PPh₃ )₄ and lithium t ‐butoxide to produce various di‐substituted aryl olefins in moderate to good yields.     

New Synthetic Technology for the Mild and Selective One-Carbon Homologation of Hindered Aldehydes in the Presence of Ketones

A selective, mild, and highly efficient method has been uncovered during the total synthesis of the CP molecules to accomplish the one-carbon homologation of sterically hindered aldehydes in the presence of acid- and base-labile moieties, Michael acceptors, and even other carbonyl groups such as reactive and epimerizable ketones. Mechanistic studies have revealed a neutral reagent for the rapid collapse of cyanohydrins to ketones.     

稀土金属作用下芳香醛、酮的还原偶联反应

由Ln/ROH/TMSCl组成的体系能选择性地使芳香族醛、酮还原偶联形成频哪醇, 产率优良, 而对脂肪族醛酮呈惰性。     

Chemoselective Preparation of Oximes, Semicarbazones, and Tosylhydrazoneswithout Catalyst and Solvent

Summary.  A simple and versatile method for the synthesis of oximes, semicarbazones, and tosylhydrazones of aldehydes in the presence of ketones without catalyst and solvent is presented. Received June 28, 2000. Accepted (revised) August 25, 2000     

Oxidation of alcohols to carbonyl compounds with diisopropyl azodicarboxylate catalyzed by nitroxyl radicals

A nitroxyl-radical-catalyzed oxidation of alcohols using diisopropyl azodicarboxylate (DIAD) as the terminal oxidant is reported. A variety of primary and secondary alcohols including aliphatic, benzylic, and allylic alcohols are efficiently oxidized to their corresponding aldehydes and ketones without overoxidation to carboxylic acid. 1,2-Diols are oxidized to hydroxyl ketones or diketones depending on the amount of DIAD used.     

tert-Butylnitrite as a convenient and easy-removable oxidant for the conversion of benzylic alcohols to ketones and aldehydes

The oxidation of primary and secondary benzylic alcohols was achieved by using tert-butyl nitrite (t-BuONO) as a stoichiometric oxidant. Various substrates were effectively converted into the corresponding ketones or aldehydes in good to excellent yields. The reaction presumably proceeded by a nitrosyl exchange and a subsequent thermal decomposition of benzylic nitrites. This process would realize an oxidation of alcohols with oxygen in theory by combining with a reproduction of alkyl nitrites from NO and alcohols under an O₂ atmosphere. In addition, almost pure oxidized products were readily obtained by simple evaporation of the reaction mixtures since t-BuONO produced only volatile side products.     

A chemoselective aerobic oxidation of benzylic azides catalyzed by molybdenum xanthate in an aqueous medium

A mild molybdenum-catalyzed, aerobic, chemoselective oxidation of benzylic azides to the corresponding aldehydes in an aqueous medium that tolerates a variety of functional groups including alcohols, esters, ketones, halides and olefins is described.     

General and practical conversion of aldehydes to homologated carboxylic acids

The reaction of aldehydes with trichloromethide followed by sodium borohydride or sodium phenylseleno(triethyl)borate under basic conditions affords homologated carboxylic acids in high yields. This operationally simple procedure provides a practical, efficient alternative to other homologation protocols. The approach is compatible with sensitive aldehydes including enals and enolizable aldehydes. It also offers convenient access to alpha-monodeuterated carboxylic acids.     

A stabilized formulation of IBX (SIBX) for safe oxidation reactions including a new oxidative demethylation of phenolic methyl aryl ethers

[reaction: see text] SIBX is a nonexplosive formulation of IBX that can be used as a suspension in a variety of standard organic solvents such as refluxing EtOAc and THF to oxidize safely alcohols into aldehydes and ketones. The use of hot THF is limited to the oxidation of allylic and benzylic alcohols. Most yields are comparable to those obtained with IBX or DMP. SIBX can also be used to perform oxygenative demethylation of 2-methoxyarenols into orthoquinones and catechols.