Enol Ester Synthesis via Cobalt-Catalyzed Regio- and Stereoselective Addition of Carboxylic Acids to Alkynes

Abstract

A cobalt-catalyzed highly regio-and stereoselective hydro-oxycarbonylation of alkynes is reported. Both terminal and internal alkynes can react with carboxylic acids to afford enol esters in high yields. The catalyst generated from Co(BF 4 ) 2 , tridentate phosphine ligand L5, and zinc in situ exhibits much higher reactivity than the corresponding cobalt/diphosphine complex.

Revealing the Strong Relationships between Ligand Conformers and Activation Barriers: A Case Study of Bisphosphine Reductive Elimination

“…Transition metal catalysts have enabled a variety of cross-coupling reactions and are an indispensable tool for C–C and C–heteroatom bond formation. For select cross-coupling reactions, bidentate phosphine ligands in particular are known to impart highly useful degrees of stereo- and regiocontrol. − For example, bisphosphine nickel complexes are established, high-performing catalysts for synthesizing conjugated polymers by enchaining thiophene and other aromatic monomers . This reaction depends sensitively on a number of required steps, including transmetalation, reductive elimination, and chain-walking, that must proceed in a controlled manner to obtain polymers with desirable materials properties.…”

Cobalt-Catalyzed gem-Cross-Dimerization of Terminal Alkynes

“…To develop a selective cross-dimerization of two different terminal alkynes, the catalyst must control three processes in case of metal acetylide mechanism: (1) selective metal-acetylide formation with one of the two terminal alkynes; (2) coordination of metal-acetylide with only the other alkyne to avoid homodimerization; and (3) regioselectivity in the acceptor alkyne (gem or linear) (Figure ). During our investigation on the Co­(I)-catalyzed enol ester formation between alkynes and carboxylic acids, we observed the 1,3-enyne formation from phenylacetylene with Co­(OAc) 2 /triphos when no reducing Zn was added. We were aware that the OAc ligand in the Co­(II)/triphos complex may function as an internal base to promote the cobalt-acetylide formation.…”

A Facile Transition Metal‐Free Ionic Liquid [BMIM]OH Mediated Regio‐ and Stereoselective Hydrocarboxylation of Alkynylnitriles

“…Therefore, the main focus of the ongoing research has been devoted towards the efficient synthesis of widely substituted stereo‐defined enol esters, by the use of specific reagents and catalysts. A large number of transition metal complexes of ruthenium, [3b–d,4] palladium, [5] rhodium, [6] iridium, [7] cobalt, [8] rhenium, [9] silver, [10] iron, [11] copper, [12] and mercury [13] are utilized for the hydrocarboxylation of the alkynes to synthesize substituted enol esters. However, it has been observed that the regio‐ and stereoselectivity of the metal catalyzed organic transformations strongly depends on the ligand environment around the metal centre.…”