Nickel-Catalyzed Acyl Group Transfer of o-Alkynylphenol Esters Accompanied by C-O Bond Fission for Synthesis of Benzo[b]furan

摘要

Herein, we report the nickel-catalyzed cascade C-O bond cleavage/cyclization of ortho-alkynylphenyl ester to construct a 3-acylbenzo[b]furan skeleton. As a result of reaction condition screening, the Ni(0)/IAd (1,3-Di(1-adamantyl)imidazole-2-ylidene) system was found to be optimal for catalytic conversion. Interestingly, the reaction exclusively gives 3-acylbenzo[b]furan instead of a decarbonylated product frequently observed in reactions mediated by acyl-nickel species. The catalyst loadings could be reduced to 5-10 mol %. We demonstrated the synthesis of a variety of functionalized 3-acylbenzofuran derivatives. We conducted stoichiometric study of nickel complexes as well as density functional theory (DFT) calculations to support a possible reaction mechanism.