Direct Carboxylation of the Diazo Group ipso-C(sp)-H bond with Carbon Dioxide: Access to Unsymmetrical Diazomalonates and Derivatives.

The direct carboxylation of the ipso-C(sp)-H bond of a diazo compound with carbon dioxide under mild reaction conditions is described. This method is transition-metal-free, uses a weak base, and proceeds at ambient temperature under atmospheric pressure in carbon dioxide. The carboxylation exhibits high reactivity and is amenable to subsequent diversification. A series of unsymmetrical 1,3-diester/keto/amide diazo compounds are obtained with moderate to excellent yields (up to 99%) with good functional group compatibility.