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.