Experimental test of the [3+2]- and [2+2]-cycloaddition pathways for the bis-cinchona alkaloid-OsO4 catalyzed dihydroxylation of olefins by means of C-12/C-13 kinetic isotope effects

The C-12/C-13 kinetic isotope effects for the bis-cinchona-OsO4 catalyzed dihydroxylation of 4-nitrostyrene, 4-methoxystyrene and allyl 4-methoxybenzoate have been measured at the olefinic carbons by the method of Singleton. For each olefin, the C-12/C-13 kinetic isotope values are substantial and similar at the two olefinic carbons. These results accord well with prediction based on a [3+2] cycloaddition pathway but not with expectations for a [2+2] cycloaddition process. Copyright (C) 1996 Elsevier Science Ltd