Visible-Light-Induced Radical [4 + 1] Annulation of Diazosulfonium Triflates with Cyclopropenes: Direct Synthesis of Benzofulvenes

A visible-light-induced radical [4 + 1] annulation of diazosulfonium triflates and cyclopropenes has been established. In this process, diazomethyl radicals generated from diazosulfonium triflates undergo addition to cyclopropenes, followed by ring opening of the resulting cyclopropyl radicals bearing a diazo functionality to form alkenyl radical intermediates, which subsequently participate in intermolecular cyclization. This transformation proceeds under mild reaction conditions and provides an effective approach for the construction of benzofulvene frameworks from easily accessible substrates.