Mechanistic Aspects of Alkyne Migration in Alkylidene Carbenoid Rearrangements

The mechanism of the Fritsch-Buttenberg-Wiechell rearrangement of C-13 labeled precursors has been examined to determine the propensity of the alkynyl (R-C C-) group to migrate in an alkylidene carbenoid species. Reaction of dibromoolefins with n-BuLi and ketones with Me3SiC(Li)N-2 both demonstrate that the alkynyl moiety readily undergoes 1,2-migration from carbenoid intermediates.