One-pot two step synthesis of unsymmetrically substituted indenes from 3,4-diarylbutadiene sulfones

A new one-pot two step synthesis of unsymmetrically substituted indenes from available 3,4-diarylbutadiene sulfones involves SO₂ thermal extrusion followed by acid- catalyzed cyclization of the diene formed, the cyclization proceeding selectively at the more electron-rich aryl rings. The procedure is efficient for substrates bearing donor, acceptor, as well as bulky substituents.