Regiocontrol by electron withdrawing groups in the Rh-catalyzed C H insertion of α-diazoketones

It is possible to control the regiochemistry of the Rh-catalyzed insertion of α-diazoketones into CH bonds by taking advantage of the greatly reduced rate of insertion into methylenes which are α or β to a carboxyl function. The 2-carboxyethyl group is especially useful for this purpose because it can be transformed eventually into a variety of other substituents.