Evidence for the intermediacy of an alkyne rather than an allene in the base-induced reaction of 3-bromo-6,7-benzobicyclo[3.2.1]octa-2,6-diene

In order to reveal the real intermediate in the base-promoted reaction of 1 , 2-methyl derivative 16 has been synthesized and its HBr elimination react ion studied. Reaction of 16 with potassium t-butoxide did not form the corr esponding allene intermediate 17 under the same reaction conditions as desc ribed for 1. Under more drastic conditions exocyclic diene 18 was formed, T hese results provide evidence for the intermediacy of the alkyne 3 in the b ase-promoted reaction of 1. (C) 1999 Published by Elsevier Science Ltd. All tights reserved.