Silver-Mediated Intermolecular [2 + 2 + 1] Cyclization of Terminal Alkynones with Elemental Selenium: Regioselective Synthesis of 2,4- or 3,4-Dicarbonylselenophenes

An efficient and atom-economical silver-mediated [2 + 2 + 1] cyclization protocol for the selective synthesis of 2,4- or 3,4-dicarbonylselenophenes has been developed. Readily accessible substrates, commercially available elemental selenium, and good functional group tolerance make this procedure attractive for the selective synthesis of dicarbonylselenophenes. Preliminary mechanistic investigations indicated that silver acetylene species are possible intermediates for the formation of 3,4-dicarbonylselenophenes.