RELEVANCE OF OXYANION STEREOCHEMISTRY TO CHIRALITY TRANSFER IN ANIONIC OXY-COPE REARRANGEMENTS

Geometrically and optically pure (3R,5E)- and (3R,5Z)-1,5-heptadien-3-ols undergo anionic oxy-Cope rearrangement under the exclusive control of oxyanion orientation with a 58-64% preference for equatorial oxygen. Six semicyclic dienols have also been synthesized where the preferred oxyanion-driven sigmatropic rearrangement pathway is obligatorily pitted against pi-facial biases offered by 4-tert-butylcyclohexenyl, norbornenyl, and camphenyl rings. These rearrangements therefore offer especially stringent tests of those factors that control the level and direction of chirality transfer. The data show the oxyanion to disfavor becoming involved in 1,3-diaxial relationships. Electronic factors may also contribute to the stabilization of axial oxyanion orientation. If operative, this effect cannot be large and is easily overridden. The observed preferences show that a change in relative carbinol configuration can indeed have a significant impact on the isomeric distribution obtained from the anionic oxy-Cope rearrangement.