Regioselective anionic [3+2] cyclizations of isoxazole, pyrazole and 1,2,4-triazole dinucleophiles - Efficient synthesis of 2,4-dihydroimidazo-[4,5-b]quinoxalines, 3H-imidazo[1,2-b]pyrazoles and 5H-imidazo[2,1-c][1,2,4]triazoles

Regioselective cyclization reactions between oxaldiimidoyl dichlorides and 3-aminopyrazole and 3-amino-1,2,4-triazole provide convenient access to bio logically relevant 3H-imidazo[1,2-b]pyrazoles and a 5H-imidazo[2,1-c][1,2,4 ]triazole. In contrast, treatment of 3-aminoisoxazoles with diimidoyl dichl orides results in a new and efficient anionic domino process for the synthe sis of biologically relevant 2,4-dihydro-1H-imidazo[4,5-b]quinoxalines. All cyclizations proceed with high regioselectivities, which are explained wit h the aid of semiempirical computations.