Intercepting palladacycles derived by C-H insertion. A mechanism-driven entry to heterocyclic tetraphenylenes.

Mechanistic support for the intermediacy of a palladacycle, which has been implicated in the crossover Heck reaction, has been obtained by intercepting this species using biphenylene. This leads to the formation of heterocyclic tetraphenylene derivatives. Three examples of this process are reported, and in two cases, the product structures have been confirmed by X-ray crystallographic analysis.