Benzophenone Oxime Tosylate as the Photoacid Generator for the Friedel–Crafts Arylation of Aldehydes with Indoles

Photochemistry enables transformations inaccessible through ground‐state pathways. We report a sustainable and operationally simple Friedel–Crafts arylation using benzophenone oxime tosylate, in low catalyst loading, as the photoacid generator under inert conditions. The method accommodates a broad substrate scope, affording diarylmethane derivatives in good to excellent yields. Mechanistic studies elucidate key intermediates driving the transformation.