Copper-Catalyzed Cascade Synthesis of Triazoloquinoxalines

Significance

Reported is a synthetic strategy for the preparation of tricyclic 4-(trifluoromethyl)-[1,2,3]triazolo[1,5-a]quinoxalines. The copper-catalyzed cascade methodology involves a cyclo­addition between sodium azide and N-(o-halo­aryl)alkynylimines, followed by C-N bond formation. The CuI/l-proline catalyst system was identified as the most efficient one after brief optimization. Some reactions worked well (90% yield) even at room temperature, whereas others were heated up to 80 ˚C - without any readily identifiable pattern. Both the substituents on the benzene ring and alkyne were successfully varied, and it was shown, albeit only in one example each, that not only iodo-substituted benzene undergoes the cyclizative C-N bond formation, but bromo and chloro functionalities couple as well. In one ­instance, R_F = CClF₂ reacts without problems; whereas R_F = CBrF₂ leads to decomposition.