Cu-catalyzed transannulation reaction of pyridotriazoles with terminal alkynes under aerobic conditions: efficient synthesis of indolizines

The transition-metal-catalyzed denitrogenative transannulation of pyridotriazoles represents an efficient method for the synthesis of fused nitrogen-containing heterocycles. This method is based on the ability of pyridotriazole to exist in an equilibrium with diazo-form A, which can be trapped with Rh(II) to form the reactive pyridyl carbene intermediate B, capable of reacting with terminal alkynes to produce valuable indolizines 3 (Scheme 1). However, this transannulation reaction has several shortcomings. Thus, a Cl substituent at the C-7 position (AG, activating group) and an electron withdrawing ester group (EWG) at the C-3 position of the pyridotriazoles were requisite to facilitate the