Stereopure 1,3-butadiene-2-carboxylates and their conversion into non-racemic alpha-alkylidenebutyrolactone natural products by asymmetric dihydroxylation

Dienoic esters 1 with the four possible permutations of the C=C configurati ons were prepared in two steps via non-stereoselective aldol additions foll owed by stereospecific beta -eliminations. Sharpless dihydroxylations of th ese eaters yielded natural and unnatural alpha -alkylidene-beta -hydroxybut yrolactones 2. Among these were synthetic dihydromahubanolide B (cis,Z-2a), isodihydromahubanolide B (cis,E-2a) and, for the first time, litsenolide D , (ent-trans,Z-2b) and the enantiomer trans,E-2b of litsenolide D-2. Compet itively, dihydroxyesters 10 were formed. (C) 2001 Elsevier Science Ltd. Al rights reserved.