Glyoxylic menthyl ester

Fiaud and Kagan 125) condensed glyoxylic acid menthyl ester with benzylamine or a-substituted benzylamines to form the corresponding N-benzyliminoacetic acid menthyl esters. 

Two groups have investigated N-sulfonyl imines of glyoxylate esters, derived from scalemic alcohols, in Diels-Alder reactions [67b, 73]. Prato and coworkers reported that glyoxylate N-sulfonyl imines bearing (-)-menthyl, (-)-bornyl and (-)-8-phenylmethyl auxiliaries reacted with cydopentadiene either thermally or using Lewis acids to give only very modest diastereomeric product ratios (56 44, 53 47,60 40, respectively) [67b]. 

Reduction of the a-keto ester of an optically active alcohol, followed by hydrolysis of the a-hydroxy ester which results, yields an optically active a-hydroxy acid. Sixty years ago, for example, McKenzie (1904) reduced optically active (—)-menthyl phenyl-glyoxylate with aluminum amalgam in moist ether and obtained unequal amounts of diastereomeric (—)-menthyl mandelates. Saponification, however, gave racemic mandelic acid. Later work (McKenzie and Humphries, 1909) showed that racemization could be avoided by acetylation of the intermediate mandelate before saponification, and that reduction of (—)-menthyl phenylgly-oxylate produced mandelic acid having an excess of the R- —) enantiomer [Eq. (5)]. 

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