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

Cyclopropanes bearing contiguous all-carbon quaternary centers continue to attract attention due to their bioactivities. However, methods to obtain cyclopropanes with contiguous all-carbon quaternary centers remain largely unexplored due to the high steric hindrance of these compounds. Herein, we report a visible-light-mediated energy-transfer (EnT) strategy to realize in situ donor/donor carbenes from readily available N-tosylhydrazones, facilitating the synthesis of 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 challenging to synthesize. Detailed mechanistic reactions and DFT studies clearly demonstrated the role of the photosensitizer, the formation of donor/donor carbenes, and the necessity of light and a base in the system.