Modular Enantioselective Synthesis of cis-Cyclopropanes through Redox-Active Carbene Transfer and Stereoselective Photo-Decarboxylation

Chiral cis-cyclopropanes are strained rigid analogs of alkyl chains, whose study and application is still limited by their difficult synthesis. A modular approach for the synthesis of this challenging structures from abundant olefins is enabled by the discovery of the electron donor-acceptor (EDA) interaction between 2-substituted benzothiazolines and N-hydroxyphtalimide esters. These complexes are activated by visible light without photocatalysts. In this system, the benzothiazoline reagent plays a triple role as photoreductant, stereoselective hydrogen atom donor and Brønsted acid. Beyond the enantioselective synthesis of cis-cyclopropanes, these results introduce benzothiazolines as accessible and easily tunable self-sensitized photoreductants.