Fischer Indolization of Ethyl Pyruvate 2-[2-(Trifluoromethyl)phenyl]-phenylhydrazone and New Insight into the Mechanism of the Goldberg Reaction. (Fischer Indolization and Its Related Compounds. XXVI)

The Fischer indolization of ethyl pyruvate 2-[2-(trifluoromethyl)phenyl]phenylhydrazone (5) gave two indolic products, ethyl 7-(trifluoromethyl)-1-phenylindole-2-carboxylate (12) as a minor product and ethyl 1-[2-(trifluoromethyl)phenyl]indole-2-carboxylate (13) as a major product. This result shows that the Fischer indolization occurred on the more electron-rich phenyl group. In the Goldberg reaction to prepare 13 from ethyl indole-2-carboxylate (15) and o- (21) or m-bromo-α, α, α-trifluotoluene (23), it was found that Goldberg reaction proceeds via a benzyne mechanism, at least in part, in a sterically crowded situation.