Visible‐Light Mediated [4+2] Annulation of o‐Alkynylated ConjugateChalcones for Synthesis of 3,4‐Disubstituted‐Fluorenones

The method of photochemical [4+2] annulation of triplet states 1,6‐dieneynes to fluorenones via energy transfer (EnT) process under visible light irradiation is introduced. The EnT process between rose bengal and substrate is well supported by Stern–Volmer experiments. Control experiments and radical scavenging studies are well supported to rationale the reaction mechanism. This protocol showed high functional group tolerance and high atom economy.