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-≥99% ee) readily available via asymmetric allylboration were converted into p-nitrobenzoate esters and subjected to hydroboration followed by oxidation with CrO 3 in aqueous acetic acid (10% H 2 O) 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 γ-substituted γ-butyrolactones (5) (R=Me, Pr, i-Pr, t-Bu, Ph, (E)-CH=CHCH 3 ) usually without racemization and in good yields