SYNTHETIC OPPORTUNITIES OFFERED BY ANTI ALPHA-METHYLENE-BETA-HYDROXY-GAMMA-ALKOXY ESTERS - STEREOSELECTIVE REACTIONS AT THE DOUBLE-BOND

Addition of tert-butyl @-(dimethy1amino)propionate to (S)-0-[( benzyloxy)methyl]lactaldehydea nd (R)-2,3- 0-isopropylideneglyceraldehyde gave, after N-methylation and elimination, a-methylene-@-hydroxy-y-alkoxy esters in fairly good yield (4040%) and a high anti-syn ratio (7-12:l). These esters were easily lactonized, by acidic treatment, to the corresponding a-methylene-@-hydroxy-y-butyrolactonesT.h e double bond of these compounds was submitted to various reactions (cuprate addition, reduction, dihydroxylation). The stereoselectivity of these reactions was studied and ranged from poor to good depending on the specific substrate and reaction used. Acyclic substrates proved to be more selective than the corresponding y-lactones. The stereoconfiguration of the products was assigned by comparison to known compounds (blastmycinolactol-a, epi-D-hamamelose).