Visible-Light-Mediated Energy Transfer Enables Cyclopropanes Bearing Contiguous All-Carbon Quaternary Centers

Cyclopropanesbearing contiguous all-carbon quaternary centerscontinue to attract attention due to their bioactivities. However,methods to obtain cyclopropanes with contiguous all-carbon quaternarycenters remain largely unexplored due to the high steric hindranceof these compounds. Herein, we report a visible-light-mediated energy-transfer(EnT) strategy to realize in situ donor/donor carbenes from readilyavailable N-tosylhydrazones, facilitating the synthesisof highly congested EWG-free cyclopropanes. Through this approach,cyclopropanes are rapidly installed into complex bioactive molecules,fluorescent molecules, and other useful building blocks that are challengingto synthesize. Detailed mechanistic reactions and DFT studies clearlydemonstrated the role of the photosensitizer, the formation of donor/donorcarbenes, and the necessity of light and a base in the system.