The Efficient Synthesis of Benzannulated Seven-Membered O-Heterocycles via the Intramolecular Ring-Opening Cyclization of Cyclopropanes.

An efficient and practical approach for the synthesis of substituted benzannulated seven-membered O-heterocycles from cyclopropane derivatives is described. The transformation proceeds via Lewis acid mediated ring opening of cyclopropanes followed by a concomitant 7-endo-tet cyclization to furnish the 4-benzoyl-3,4-dihydrobenzo[b]oxepin-5(2H)-one derivatives in excellent yields (up to 92%). This potentially general method is featured by its high atom economy, broad substrate scope, and mild reaction conditions. Moreover, the representative products exhibited selective antifungal activity in vitro against the fungus Cryptococcus neoformans. Therefore, the present reaction will be useful for the development of novel antifungal therapeutic reagents.