Access to cyclobutane–fused dihydrobenzothiophenes via gold–mediated photocatalyzed [2+2]–cycloaddition reactions

The use of [Au(SIPr)(Cbz)] as photosensitizer in [2+2]–cycloaddition reactions between benzothiophenes and activated and non–activated alkenes is presented. Commonly used organic and Ir–photosensitizers proved inefficient in the reaction with non–activated alkenes. The study emphasizes the dependence on the nature of the alkene, a parameter that has previously received little attention. Under mild reaction conditions, a wide array of alkenes and benzothiophenes were successfully coupled, showcasing remarkable tolerance of diverse functional groups. Additionally, we present intramolecular [2+2]–cycloaddition reactions, including benzothiophenes featuring various alkene linkers at the C2 and C3 positions.