Photochemical [2+1]-Cycloadditions of Nucleophilic Carbenes

Visible light induced singlet nucleophilic carbene intermediates undergo rapid [2+1]-cycloaddition with tethered olefins to afford unique bicyclo[3.1.0]hexane and bicyclo[4.1.0]heptane scaffolds. This cyclopropanation proceeds using only visible light irradiation, circumventing the use of exogenous (photo)catalysts or sensitisers and showcases an underexplored mode of reactivity for nucleophilic carbenes in chemical synthesis. The discovery of additional transformations including a cyclopropanation/retro-Michael/Michael cascade reaction to afford chromanone derivatives are also described.