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 % ee s 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)