STEREOSELECTIVE SYNTHESES AND REACTIONS OF CHIRAL OXYGENATED ALPHA,BETA-UNSATURATED-GAMMA-LACTONES AND DELTA-LACTONES

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