HIGHLY DIASTEREOSELECTIVE ELECTROPHILIC ADDITIONS TO THE VINYLCYCLOPROPANE MOIETY OF A HOMOTROPYLIDENE SYSTEM

The acid catalyzed addition of AcOH and MeOH to the vinylcyclopropane moiety of tracyclo[5.3.2.0(2,10).0(3,6)]dodeca-4,8,11-triene (1) affor ded kinetic mixtures of 9-acetoxy and, respectively. methoxytricyclo[4 .3.3.0(2,5)]dodeca-3,7,10-trienes in which the beta derivatives are al ways. even when sterically more congested, highly prevalent over their a counterparts. Studies with deuterated acetic acid showed that there was not any relationship between the stereochemistry of the deuteron (proton) attack and that of the nucleophilic trapping of the intermedi ate carbocation. These findings can be rationalized on the basis of a two step process i) proton attack to the homotropylidene moiety of 1 w ith formation of a cyclopropylcarbinyl carbocation ii) opening of its cyclopropane ring under tight assistance by the nucleophilic solvent t o give the final products with high beta diastereoselectivity. By cont rast, the reaction of dichloroketene, a strong uniparticulate electrop hile, involved only the cyclobutene system of 1. (C) 1997 Elsevier Sci ence Ltd.