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

Abstract

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.

Palladium-Catalyzed Intramolecular Migratory Cycloisomerization of 3-Phenoxy Acrylic Acid Ester <i>via</i> C–O Bond Cleavage and C–O/C–C Bonds Formation for 2,3-Disubstituted Benzofurans Synthesis

“…However, both used Ni catalysts. 20,22) Here, we report unprecedented Pd-catalyzed migratory cycloisomerization of 3-o-alkynylphenoxy acrylic acid derivatives to give 2,3-disubstituted benzofurans (Fig. 1, C).…”

“…Migratory groups on aromatic nitrogen in indole synthesis are carbonyl, [3][4][5][6][7] alkoxyalkyl, [8][9][10][11] propargyl, 12) allyl, 13) and sulfonyl [13][14][15][16] groups. On the other hand, migratory groups on phenol in the benzofurans synthesis are alkoxyalkyl, 8) allyl, 16) boryl, 17) vinyl 18) propalgyl, 19) and carbonyl 20) groups. Transition metals used in the migratory cycloisomerization are Pd, Ni, Ru, Rh, Au, and Pt.…”

Synthesis of 2,3‐Disubstituted Indoles by Nickel(0)‐Catalyzed Migratory Cycloisomerization of o‐Alkynylanilides

“…In 2021, we reported nickel(0)catalyzed migratory cycloisomerization of o-alkynylphenyl ester 3, giving 2,3-disubstituted benzofuran 4 (Scheme 1-(c)). [5] DFT calculation revealed that the reaction proceeded via oxanickelacyclopentene III formed by oxidative cycloaddition of alkyne and C=O bond of the ester moiety in 3 to a nickel(0) catalyst, which was successively isomerized to the intermediates IV, V, and VI, finally giving the product 4. Oxidative cycloaddition involving the C=O bond of an ester is uncommon compared with oxidative cycloaddition involving the C=O bond of aldehyde or ketone, and we therefore decided to investigate migratory cycloisomerization of oalkynylanilide 5 as the substrate instead of 3.…”

Substrate-Assisted Reductive Elimination Determining the Catalytic Cycle: A Theoretical Study on the Ni-Catalyzed 2,3-Disubstituted Benzofuran Synthesis via C–O Bond Activation

“…Therefore, the kinetically favorable pathway and full catalytic cycle remain unclear. Although several theoretical studies on C–O bond activation mechanisms by Ni complexes (e.g., C­(phenyl)–O bond activation) − have been reported, theoretical studies on Ni-catalyzed C­(vinyl)–O bond activation mechanisms are rather limited to the best of our knowledge. In the present study, we thus investigated the full catalytic cycle in the synthesis of Ni-catalyzed 2,3-disubstituted benzofurans using DFT calculations.…”