OPTICALLY-ACTIVE KETONES AS CHIRAL AUXILIARIES IN THE [2,3]-WITTIG REARRANGEMENT

The stereochemical aspects of the [2,3]-Wittig rearrangement of optically active tertiary allyl ethers derived from (+)-camphor and (-)-fenchone were investigated. The rearrangement of the (+)-camphor derivative yielded two olefin products in a 70/30 E/Z ratio. The geometry of the trisubstituted olefin produced during the rearrangement was assigned by NOE experiments. The configuration of the newly formed carbinol center of the products was established by kinetic resolution, Mosher's method, and conversion to derivatives of known absolute configuration. The absolute configuration of the carbinol center for the Z isomer was assigned to be S and that of the E isomer to be R. The (-)-fenchone derivative gave only a single Z olefin product, which was assigned the S configuration at the carbinol center.