ELECTRONIC AND STERIC INFLUENCES ON FACE SELECTION DURING THE OXY-COPE REARRANGEMENT OF AN ALPHA-ALLYL-ALPHA-VINYLBENZYL ALCOHOL

The racemic RR, SS and RS, SR diastereomers of 5-(5-fluoroadamant-2-ylidene)-4-hydroxy-4-phenyl-l-pentene (1-F) have been synthesized. Their configurations have been determined by means of 13C NMR as well as by way of an X-ray diffraction study of the acetate of the former alcohol. Both alcohols undergo the oxy-Cope rearrangement to give mixtures of the (E) and (Z)-2-allyl-2-benzoyl-5-fluoroadamantanes (5-F). Analysis of these mixtures allows the conclusions to be drawn that the preferred site of the phenyl group in the chair transition states is the quasi-equatorial one, and that the electronically preferred face of the adamantyl terminus is that syn to the fluorine (zu face). These preferences amount to factors of 2.75 and 1.54, respectively. Hyperconjugation involving the incipient a orbital can account for the electronic preference observed. Pyramidalization of C2 in the acetate of 1-F was not detectible in the X-ray diffraction study. © 1990, American Chemical Society. All rights reserved.