Dual Photoredox/Gold Catalysis Arylative Cyclization of <i>o</i>‑Alkynylphenols with Aryldiazonium Salts: A Flexible Synthesis of Benzofurans

A new method for the arylative cyclization of <i>o</i>-alkynylphenols with aryldiazonium salts via dual photoredox/gold catalysis is described. The reaction proceeds smoothly at room temperature in the absence of base and/or additives and offers an efficient approach to benzofuran derivatives. The scope of the transformation is wide, and the limitations are discussed. The reaction is proposed to proceed through a photoredox-promoted generation of a vinylgold­(III) intermediate that undergoes reductive elimination to provide the heterocyclic coupling adduct

3‑Sulfonylindoles via Gold- or Silver-Catalyzed Cyclization1,3-Sulfonyl Migration Sequences under Visible Light Irradiation

A pathway for the synthesis of 3-sulfonylindoles has been devised. Upon blue LED irradiation, in the presence of a gold(I) or a silver(I) salt, ortho-alkynyl N-sulfonyl precursors readily undergo a 5-endo-dig cyclization concomitant with a 1,3-sulfonyl migration. While the gold-catalyzed reaction takes place in photocatalyst-free conditions, an iridium photocatalyst (Ir[dF(CF3)ppy]2(dtbbpy)PF6) is necessary with silver catalysis. Mechanistic studies featuring the generation of a sulfonyl radical support this dichotomy

Secondary Phosphine Oxide–Gold(I) Complexes and Their First Application in Catalysis

A series of new secondary phosphine oxide (SPO)–gold­(I) complexes have been synthesized and characterized by X-ray crystallography. Complexes exhibited dimeric structures interconnected by O–H···Cl hydrogen bonds. Their first use in homogeneous catalysis is reported and suggests a broad field of application in prototypical enyne cycloisomerization and hydroxy- and methoxycyclization reactions