Aldehydes conversion into cyanohydrins

The conversion from aldehydes 3 into a-amino cyanides 4 can go either by reaction of aldehyde 3 with ammonia or ammonium chloride to yield an intermediate 6, followed by treatment of 6 with hydrogen cyanide or an alkali cyanide, or by treatment of the cyanohydrin 7, derived from reaction of aldehyde and cyanide, with ammonia or ammonium chloride (Scheme 3). 21 ... 

RCH2.NO2 - RC=N. This conversion usually has been conducted via a Nef reaction to an aldehyde followed by formation and dehydration of an oxime. The transformation can be accomplished in one step by reaction of the primary nitro compound with PCI3 and pyridine (40-75% yield). This method can also be used to convert allylic nitro compounds into a,)3-unsaturated nitriles and to prepare aldehyde or ketone cyanohydrin acetates. 

Where reducing (aldehydic) terminals are available for reaction, they can be labelled by reduction with agents such as tritiated sodium borohydride or by conversion into a cyanohydrin with " C-labelled sodium cyanide. Alternatively, labelling with reagents such as dansyl hydrazide is possible, to yield a fluorescent derivative. 

Cyanohydrin trimethylsilyl ethers are generally useful as precursors of ctir-bonyl anion equivalents and as protected forms of aldehydes. Direct conversion of p-anisaldehyde into 0-TRIMETHYLSILYL-4-METH0XYMANDEL0-NITRILE employs a convenient in situ generation of trimethylsilyl cyanide from chlorotnmethylsilane A general synthesis of allemc esters is a variant of the Wittig reaction. Ethyl (triphenylphosphoranylidene)acetate converts pro-pionyl chloride into ETHYL 2,3-PENTADlENOATE. 

Fischer s original method for conversion of the nitrile into an aldehyde involved hydrolysis to a carboxylic acid, ring closure to a cyclic ester (lactone), and subsequent reduction. A modern improvement is to reduce the nitrile over a palladium catalyst, yielding an imine intermediate that is hydrolyzed to an aldehyde. Note that the cyanohydrin is formed as a mixture of stereoisomers at the new chirality center, so two new aldoses, differing only in their stereochemistry at C2, Tesult from Kiliani-Fischer synthesis. Chain extension of D-arabinose, for example, yields a mixture of D-glucose and o-mannose. 

Indeed the only conversion where biocatalysis should be seriously considered is the transformation of aldehydes into optically active cyanohydrins1 2. For example, the conversion of aryl aldehydes into the appropriate (R)-cyanohydrins using almond meal may be accomplished in quantitative yield and gives products... 

The conversion of aldehydes (6.53) into the corresponding cyanohydrins (6.54) is an appealing synthetic transformation, since cyanohydrins are readily converted into a number of important functional groups such as a-hydroxy acids (6.55) and P-amino alcohols (6.56). 

The Reformatskii reaction can be carried out conveniently with magnesium. If tert-huiy esters are used, the products can subsequently be transformed into satd. acids in a single operation Another easy method for the conversion of aldehydes to nitriles is their treatment with lead tetraacetate and ammonia in benzene Hydrocyanations can be efficiently performed with the help of organoaluminum compounds In this manner, steroidal cyanohydrins can be obtained from the respective epoxides by diaxial fission under mild conditions in high yield A number of addition reactions of nitrile oxides have been reported contrary to earlier reports, ar. nitrile oxides easily add hydrogen halides. 

Overall, the net result is the ability to shorten a carbohydrate chain by one carbon atom. Conversion of the aldehyde into a cyano group is accomplished via oxime formation (as seen in Section 20.6) followed by dehydration. The resulting cyanohydrin then loses HCN when treated with a strong base to afiFord the new carbohydrate that has one less carbon atom than the starting carbohydrate ... 

Various versions of the acyl anion equivalent (32) are described by Stork etal. (use of Et2NCH2CN), Krief and co-workers (1,3-dithianes in regioselective Michael addition), Gokel et al. (use of sulphur heterocycles with thermal deblocking), Cohen and Weisenfeld" (conversion of acids into vinyl sulphides), Meyers and Campbell " (acetals derived from aryl aldehydes), and Hunig and co-workers (cyanohydrin derivatives of aryl aldehydes). 

In 2001, North et al. reported the development of bimetallic Ti(IV) and V(IV) salen complexes (100) and (102) as the optimal catalysts for the asymmetric addition of trimethylsilyl cyanide to ketones and aldehydes (Scheme 16.28) [32]. Both catalysts predominantly gave the (S)-enantiomer of the cyanohydrin derivative. Complex (100) proved to be optimal for quantitative conversion of both electron rich and electron deficient ketones into the corresponding cyanohydrin trimethylsilyl ethers... 

General Synthesis and Reactions.—Linear primary alcohols with at least seven carbon atoms are transformed into esters in high yield using copper oxide at temperatures above 170 C in the liquid phase. RusfCO) catalyses the conversion of an aldehyde, or an alcohol with the same number of carbon atoms, into an ester in the presence of diphenylacetylene. " The carbonylation of organic halides in the presence of cyclic ethers is catalysed by PhPdI(PPh3)2 , it provides a synthesis of halohydrin esters in reasonable yield. Cyanohydrin esters have been synthesized by the sodium borohydride reduction of acyl cyanides in the presence of tetra-n-butylammonium bromide. ... 

A method for the preparation of amides from aldehydes by oxidation of the corresponding cyanohydrin is described this reaction is subject to the same selectivity as the previously reported method of conversion of aldehydes into esters the aldehyde must be aromatic or ajS-unsaturated to permit allylic oxidation of the cyanohydrin to the a-oxonitiile, which reacts with amines in situ to give the derived amides. 

Two procedures for the preparation of a-oxocarboxylic acids via nitrile intermediates have been described. The autoxidation of 3,3-disubstituted 2-cyanocarboxylate ester anions is reported to provide the related a-oxoesters in fair yield a new general procedure for the conversion of aldehydes into the homologous a-oxoacids is based on theoxidationof a-hydroxy-iV-t-butyl-carboxamides (116), prepared by the acid-catalysed alcoholysis of aldehyde cyanohydrins with t-butanol, to the hitherto ui nown -oxocarboxamides, which are in turn readily converted into the parent a-oxoacids on acid-catalysed hydrolysis. 

The oxidation of aldehydes to carboxylic acids by the lower valent manganese dioxide [68] is a very slow process, which requires a higher temperature [69]. Corey developed the most straightforward application of this reagent [70], which is particularly recommended for the conversion of a,(i-unsaturated aldehydes [70, 71], since it proceeds without double bond isomerization. Aromatic aldehydes can be converted into the corresponding esters [72]. The reaction involves the use of cyanide ions and proceeds via cyanohydrins. The latter are oxidized to a-ketonitriles, which undergo a cyanide substitution reaction with aUcoxide as the nucleophile to give the desired esters. 

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