Stereoselective syntheses and reactions of chiral oxygenated alpha,beta-unsaturated-gamma- and delta-lactones

The syntheses of the chiral alpha,beta-unsaturated lactones (+)-5, (-)-6, (+)-8, (+)-9, and (+)-10 have been efficiently achieved from readily available starting materials. The lactone (+)-5 has been synthesized in 7 steps from (R,R)-dimethyl tartrate (38-43% overall yield). The use of (+)-5 in formal syntheses of natural (+)-asperlin 4 and advanced intermediates for (+)-olguine 2 are also reported. The lactone (-)-6 has been prepared in 5 steps from (R)-malic acid (44-50% overall yield). It can be a useful precursor for the syntheses of branched chain and deoxy nucleoside analogues. The preparation of (-)-6 constitues formal syntheses of natural (+)-eldanolide 53 and the (+)-Geissman-Waiss lactone 54 (an intermediate for the syntheses of a variety of pyrrolizidine alkaloids). The lactones (+)-8, (+)-9 and (+)-10 have been synthesized from 3,4-di-O-acetyl-L-rhamnal 58. The highly diastereoselective transformations of (+)-9 and (+)-10, through sequential conjugate nucleophilic addition and enolate reaction, into densely functionalized chiral gamma-lactones 12 are also reported. Copyright (C) 1996 Elsevier Science Ltd