Oxidation of Aldehydes to Amides, Esters and Related Functional Groups

Oxidation of Aldehydes to Amides, Esters and Related Functional Groups 

Alkali metal t-butoxides, hydrides and bis(TMS)amides efficiently catalyse Claisen-Tishchenko disproportionation of aldehydes to the corresponding carboxylic esters. Potassium bases were more effective than sodium, and 18-crown-6 further accelerates the reaction. Kinetic studies suggest that the rate-determining step is a second-order concerted hydride transfer from a potassium hemiacetal to another molecule of aldehyde. 

In an unusual oxidative amidation of tertiary amines (typically Ar-NMc2) with aldehydes, R-CHO, amides are formed with the loss of an alkyl group. .. methyl in this case. The amide product, Ar-N(Me)CO-R, is formed in good yield using iron(II) catalysis in refluxing acetonitrile, and i-butylhydroperoxide as oxidant. 

A mechanistic investigation of aerobic esterifications of aldehydes with alcohols using NHC catalysis indicates that it is the benzoin that undergoes oxidation, and not the Bres-low intermediate, nor the NHC-aldehyde tetrahedral adduct.  

Aldehydes (R-CHO) undergo an (9-selective addition of nitrosoarenes (0=N-Ar) catalysed by NHCs this oxidative esterification yields R-C02-NHAr product in fair to good yields, with no C-N product [RCON(OH)Ar] in most cases.  

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