Enantioselective synthesis of alpha-hydroxylated enterolactone and analogs

A short and general synthesis of enantiomerically pure alpha -hydroxylated lactone lignans starting from commercially available Pr-i malate is present ed. Key reactions are two stereoselective alkylations of melic acid derivat ives. Some enhancements of the alkylation of melic acid esters and a genera l extension of the alkylation of dioxolanones is reported. Proof of the ste reochemical outcome of the alkylation reactions is provided by X-ray diffra ction analysis of alpha -hydroxy-alpha, beta -dibenzyl-gamma -butyro-lacton e, the first crystal structure of an enantiomerically pure alpha -hydroxyla ted lactone lignan. (C) 2001 Elsevier Science Ltd. All rights reserved.