Harnessing Light-Mediated Free Carbene Reactivity of Vinyldiazo Ketones: Direct Access to Mono-, Bi-, and Tricyclic 2,3-Dihydrofurans.

Despite the huge surge in visible-light-mediated transformations of diazo compounds, the free carbene transfer reactivity of vinyldiazo and α-diazoketones remains a challenge due to internally competing 2π-electrocyclization and Wolff rearrangements. Herein, we report a visible-light-induced carbene transfer strategy using a new class of vinyldiazo ketones (Br-diazoenals) that suppress competing 2π-electrocyclization and Wolff rearrangements. The free carbene transfer reaction enables cyclopropanation and Cloke-Wilson rearrangement with diverse olefins, affording enal-functionalized mono-, bi-, and tricyclic 2,3-dihydrofurans under mild conditions. The synthetic utility of the products has been demonstrated through the late-stage modification and rapid synthesis of analogues of bioactive molecules, highlighting their potential in drug discovery.