Gold(I) Catalysis Under Visible Light

This thesis has focused on the study of a dual catalytic process involving gold catalysis and photocatalysis. We aimed to synthesize benzofuran derivatives from o-alkynylphenols and aryl diazonium salts or iodoalkynes in the presence of a catalytic mixture of a gold(I) complex and a photocatalyst under visible light irradiation. Firstly, we present a novel dual photoredox/gold catalysis process by arylative cyclization of o-alkynylphenols with aryldiazonium salts. This reaction occurs smoothly at room temperature in the absence of base and/or additives and offers an efficient approach to heterocyclic scaffolds. The reaction is proposed to proceed through a photoredox-promoted generation of a vinylgold(III) intermediate, formed by addition of the aryl radical to the gold catalyst and modulation of the oxidation state by the photocatalyst, which undergo reductive elimination to provide the heterocyclic coupling adduct. Later, we developed a new method for the synthesis of valuable alkynyl benzofuran derivatives devised from o-alkynylphenols and iodoalkynes in the presence of a catalytic mixture of Au(I) and Ir(III) under blue LED irradiation. Under visible light irradiation, the triplet excited state of the vinylgold(I) intermediate and the alkynyl iodide partner readily engaged in a oxidative addition–trans/cis isomerization sequence, deliver Csp2-Csp cross coupling products after reductive elimination. An energy transfer event rather than a redox pathway was demonstrated by the mechanistic and modeling studies. This dual gold/photo catalytic process provides a novel mode of activation in gold homogenous catalysis.