CHIRAL SYNTHESIS VIA ORGANOBORANES .39. A FACILE SYNTHESIS OF GAMMA-SUBSTITUTED-GAMMA-BUTYROLACTONES IN EXCEPTIONALLY HIGH ENANTIOMERIC PURITY

Optically active homoallylic alcohols of exceptionally high enantiomeric purity (98-greater than or equal to 99 % ee) readily available via asymmetric allylboration were converted into p-nitrobenzoate esters and subjected to hydroboration followed by oxidation with CrO3 in aqueous acetic acid (10% H2O) to obtain the corresponding carboxylic acids with the same number of carbon atoms. The protecting ester group was hydrolyzed and the product lactonized in situ to the gamma-substituted gamma-butyrolactones 5 (R = Me, Pr, i-Pr, t-Bu, Ph, (E)-CH=CHCH3) usually without racemization and in good yields. The method is convenient and potentially valuable for. the synthesis of highly functionalized gamma-butyrolactones in high optical purity.