Herein, we report the nickel-catalyzed cascade CÀ 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-2ylidene) system was found to be optimal for catalytic conversion. Interestingly, the reaction exclusively gives 3acylbenzo[b]furan instead of a decarbonylated product fre-quently 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 3acylbenzofuran derivatives. We conducted stoichiometric study of nickel complexes as well as density functional theory (DFT) calculations to support a possible reaction mechanism.
We herein report a nickel-catalyzed migratory cycloisomerization of o-alkynylanilides, giving 2,3-disubstituted indoles in good yields. The cyclization proceeded via acyl transfer on the nitrogen atom of the substrate to C3position in the product, and an N-heterocyclic carbene (NHC) ligand such as ICy or SICy was found to be suitable in this reaction. It was thought that the reaction proceeds via an aza-nickelcyclepentene intermediate formed from alkyne and the C=O bond of the amide moiety in o-alkynylanilides.
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