Dichloromethane as C1 Synthon for the Photoredox Catalytic Cyclopropanation of Aromatic Olefins

Dichloromethane, as a readily available and inexpensive C1 synthon is proposed as a powerful building block for cyclopropanation of alkenes under mild conditions. Herein, we report a highly efficient and versatile dual photoredox system, involving a nickel aminopyridine coordination complex and a photocatalyst, for the cyclopropanation of aromatic olefins using dichloromethane, under visible‐light irradiation. The cyclopropanation protocol has been successfully applied at gram scale. Mechanistic studies suggest a Ni(II) pyridyl radical complex as the key intermediate for the homolytic cleavage of the Csp3−Cl bond, generating a chloromethyl radical that is captured by the olefin coupling partner. Our findings also highlight the versatility of this methodology. By directing the radical/polar crossover process, we were able to selectively drive the reaction towards either the formation of cyclopropyl derivatives or the corresponding non‐cyclic alkyl chloride products. The methodology also successfully apply to geminal dichloroalkanes, including the formation of spiro[2,2] compounds. Moreover, our methodology extends to the synthesis of deuterium‐labelled cyclopropanes, demonstrating its utility in isotopic labelling and broadening its applicability in chemical synthesis and drug development.