Enantioselective Intermolecular Photocycloaddition of Indoles

The synthesis of cyclobutane‐fused heterocycles via photocycloaddition (PCA) of heteroarenes has been widely explored. However, achieving high enantioselectivity remains challenging. Represented herein is a report on an efficient and enantioselective intermolecular [2+2] cycloaddition of indoles with various alkenes and aryl allenes under visible light irradiation. A chiral oxazaborolidinium ion ( COBI ) was used to engage indole substrates via efficient B COBI −O sub coordination. Upon photoexcitation, the resulting adduct undergoes radical addition to alkenes, the enantio‐determining step, followed by radical recombination to afford cyclobutane products. This strategy significantly expands substrate compatibility and functional group tolerance, providing an efficient and versatile route to enantioenriched cyclobutane‐fused heterocycles.