A triple cascade process was developed for the rapid synthesis of polycyclic benzo-fused dihydrofurans. The first step is a rhodium-catalyzed cyclopropanation of α-aryldiazoketones with alkenes. This is followed by a silver-catalyzed ring expansion to dihydrofurans, which then undergo a gold-catalyzed cyclization to form benzo-fused dihydrofurans.
[Duong, Hung A.; Gilligan, Ruth E.; Cooke, Michael L.; Phipps, Robert J.; Gaunt, Matthew J. Angewandte Chemie - International Edition, 2011 , vol. 50, # 2 p. 463 - 466]
