Abstract
It was found that direct hydrolysis of the crude oxazolidine derivatives (3a, b), prepared with dl-α-cyclocitral (dl-1a), or its 6-benzoxy derivative (dl-1b) and (S) (+)-prolinol ((S) (+)-4), with aqueous acetic acid, afforded (R) (+)-1a, 19% optically pure, and (S) (+)-6-hydroxy-α-cyclocitral ((S) (+)-2b), 63% optically pure, respectively. A merit of the resolution method is that optically active (R) (+)-1a or (S) (+)-2b can be obtained without any recrystallizations. Some mechanistic studies and discussions on the hydrolysis were also examined. Optically active (S) (+)-2b, thus obtained, was successfully converted into (S) (+)-dehydrovomifoliol ((S) (+)-5) via (S) (+)-6-hydroxy-α-ionone ((S) (+)-9). By this chemical conversion, (S) (+)-abscisic acid could be formally synthesized from dl-1b.
