Highly diastereoselective electrophilic additions to the vinylcyclopropane moiety of a homotropylidene system

Abstract

The acid catalyzed addition of AcOH and MeOH to the vinylcyclopropane moiety of tetracyclo[5.3.2.0 2,10 .0 3,6 ]dodeca-4,8,11-triene ( 1 ) afforded kinetic mixtures of 9-acetoxy and, respectively, 9-methoxytricyclo[4.3.3.0 2,5 ]dodeca-3,7,10-trienes in which the β derivatives are always, even when sterically more congested, highly prevalent over their α 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 intermediate carbocation. These findings can be rationalized on the basis of a two step process i) proton attack to the homotropylidene moiety of 1 with formation of a cyclopropylcarbinyl carbocation ii) opening of its cyclopropane ring under tight assistance by the nucleophilic solvent to give the final products with high β diastereoselectivity. By contrast, the reaction of dichloroketene, a strong uniparticulate electrophile, involved only the cyclobutene system of 1 . Graphic