Enantioselective Butenolide Preparation for Straightforward Asymmetric Syntheses of γ-Lactones – Paraconic Acids, Avenaciolide, and Hydroxylated Eleutherol

The naturally occurring γ-lactones (+)-methylenolactocin (13) and its enantiomer, (+)-protolichesterinic acid (14) and its enantiomer, (+)-rocellaric acid (15), and the methylene bis(γ-lactone) (–)-avenaciolide (16) were synthesized with 95–98 % ees in very few steps. Enantiocontrol was imposed by the asymmetric dihydroxylation of trans-configured β,γ-unsaturated carboxylic esters (namely compounds 1i, 1j, and 1n) with AD mix-α® [for the levorotatory target structures, except for (–)-avenaciolide] or AD mix-β® [for the dextrorotatory target structures plus (–)-avenaciolide]. β,γ-Unsaturated carboxylic ester 1e required increased amounts of the oxidant and auxiliary to produce the hydroxy lactone R,R-3e, a precursor of the naphtho-γ-lactone (+)-9-hydroxyeleutherol (12; 96 % ee). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)