Nickel-Mediated Regio- and Chemoselective Carboxylation of Alkynes in the Presence of Carbon Dioxide

Abstract

Alkynes are carboxylated in a highly regio- and chemoselective manner in the presence of Ni(cod)2, DBU, and CO2 to give the carboxylated products in good yields. The reaction was carried out under very mild conditions (CO2 1 atm, 0 °C) in the presence of a stoichiometric amount of alkynes, conjugated enynes, or diynes. The high selectivity observed in the reaction would be explained in terms of the stability and the reactivity of the intermediates.

Ni- and Fe-catalyzed Carboxylation of Unsaturated Hydrocarbons with CO2

“…The reaction proceeded under mild conditions and a wide range of organozinc reagents could be used leading to β,β'-disubstituted unsaturated carboxylic acids with an excellent regioselectivity profile that goes in line with the hydrocarboxylation procedure reported by Yamamoto and Saito (Scheme 6). [36]. Notably, the authors found that heterocyclic structures were within reach by appropriately locating a tethered heteroatom on the side-chain, thus setting the stage for an intramolecular Michael addition [39,40].…”

“…Gibbs free energies (kcal/mol) for the coupling of CO 2 with acetylene [34] [36]. In this work, the authors disclosed the stoichiometric carboxylation of terminal alkynes with in situ formed Ni(DBU) 2 , leading to the rapid formation of β-substituted carboxylic acids with high levels of chemo-and regioselectivity (Scheme 3).…”

“…This reaction could be applied to differently substituted alkynes bearing aromatic, aliphatic or silyl groups with equal ease. [36] The regioselectivity observed in the oxidative cyclization of monosubstituted alkynes with CO 2 was theoretically rationalized by Buntine (Scheme 4) [34]. The authors observed a markedly different energetic preference for the two possible transition states (TS-I and TS-II), with a lower energy barrier for TS-I leading to I, in which CO 2 insertion takes place distal to the substituent on the alkyne motif.…”

“…Kinetic studies by Geyer and Schindler using isoprene as model compound highlighted the importance of the ligands employed, suggesting that future catalytic variants should be focused on ligand design [117]. Furthermore, Saito, Yamamoto and co-workers showed that mono-carboxylation of 1,3-unsaturated backbones can be accomplished using enynes and diynes, in which CO 2 insertion occurred at the alkyne terminus and at the less-hindered site [36].…”

Carbon Dioxide as a Carbon Resource – Recent Trends and Perspectives

“…Much pioneering work on catalytic CO 2 chemistry was conducted around the world including the groups of Behr [22 -27], Hoberg [28 -35], Walther [36,37], and Dinjus [38 -42], as well as Inoue [43 -47], Musco [48], Yamamoto [49,50], Darensbourg [51,52], and others [53 -57]. These efforts have developed a fundamental understanding of the chemistry of metal complexes with CO 2 providing a sound basis for the rational development of catalytic transformations of this raw material.…”