Process for the preparation of dihydroxycarboxylic acid esters in the absence of solvents

摘要

Production of dihydroxycarboxylic acid esters, by reaction of hydroxycarboxylic acid diesters with complex hydrides, is conducted in the absence of a solvent. Production of dihydroxycarboxylic acid esters of formula (I) by reaction of hydroxycarboxylic acid diesters of formula (II) with complex hydrides is conducted in the absence of a solvent. n = 1, 2, 3, 4, 5, 6 or 7; and R<1> and R<2> = optionally substituted 1-20C alkyl, 2-20C alkenyl or alkynyl, 3-8C cycloalkyl, aralkyl, aryl, hetarylalkyl or hetaryl An Independent claim is included for production of R-(+)- alpha -lipoic acid of formula (III) from (I) obtained as above (i.e. in the absence of solvent) by: (1) converting (I) to its bis-sulfonic ester by reaction in an organic solvent with a sulfonic acid chloride and a tertiary nitrogen base; (2) converting the ester thus obtained to R- alpha -lipoic acid ester by reaction in a polar solvent with sulfur and an alkali metal disulfide; and then (3) converting the ester to the required product.