cis-Selective Direct Halocyclopropanation of Alkenes Mediated by Nucleophilic Cobalt Photocatalysis.

The cyclopropyl group is an invaluable motif in both medicinal and synthetic chemistry, with 1,2-disubstituted halocyclopropanes serving as important building blocks for the preparation of more complex cyclopropane-containing structures. Herein, we report a Vitamin B12-photocatalyzed approach for the direct synthesis of 1,2-disubstituted halocyclopropanes, starting from alkenes and simple haloforms under visible-light irradiation. Our method yields a diverse range of 1,2-disubstituted halocyclopropanes with high cis-selectivity, providing efficient access to these traditionally difficult-to-prepare stereoisomers. Mechanistic studies highlight the crucial role of Vitamin B12 in influencing the stereochemical outcome of the reaction.