Spin-Selective Generation of Triplet Alkenylcarbenes: Olefin Cyclopropanation Through Visible Light Photosensitization of Alkenyldiazo Compounds

Abstract

Vinyldiazo compounds are interesting precursors for generating vinylcarbenoid intermediates, but their direct photochemical activation can result in competitive formation of 1H-pyrazoles via 1,5-electrocyclization and cyclopropenes via singlet carbene-mediated 2π-electrocyclization. Herein, we report the spin-selective generation of triplet free vinylcarbenes from vinyldiazo compounds through their energy transfer with visible light-activated 4DPAIPN. The spin state of free vinylcarbenes can be controlled by introducing an electron-withdrawing group to the γ-position of vinyldiazo reagents. This strategy is applied to the cyclopropanation with exogenous alkenes, providing a photochemical metal-free approach to synthesize vinylcyclopropanes. The reaction tolerates many sensitive functional groups, such as free alcohol, secondary amine, carboxylic acid, and bioactive scaffolds.