Efficient hydrocarboxylation of alkynes based on carbodiimide-regulated in situ CO generation from HCOOH: An alternative indirect utilization of CO2

The role of carbodiimide as dehydrant in the chemo-, regio- and stereoselective Pd (II/0)-catalyzed hydrocarboxylation of various alkynes with HCOOH releasing CO in situ is reported for the first time to obtain α,β-unsaturated carboxylic acids. Both symmetrical and unsymmetrical monoalkynes show good reactivity. Importantly, 2,2'-(1,4-phenylene)diacrylic acid can also be synthesized in high yield through the dihydrocarboxylation of 1,4-diethynylbenzene. Besides, an excellent result in gram scale experiment and TON up to 900 can be obtained, displaying the efficiency of this protocol. Notably, regulating the types and concentrations of dehydrant can control the CO generation, avoiding directly operating toxic CO and circumventing sensitivity issue to the CO amount. On the basis of the attractive features of formic acid including easy preparation through CO2 hydrogenation and efficient liberation of CO, this protocol using formic acid as bridging reagent between CO2 and CO can be perceived as an indirect utilization of CO2, offering an alternative method for preparing acrylic acid analogues.