Microwave Assisted Synthesis of New Pyrrolopyridazine Derivatives with Acetophenone Skeleton. Part V

A comprehensive comparative study, microwave (MW) versus conventional thermal heating (TH), for synthesis of fused pyrrolopyridazine derivatives with dihydroxyacetophenone is described. The reaction pathway is efficient and straight applicable, involving a Huisgen [3 + 2] dipolar cycloaddition of pyridazinium ylides to activated Z-alkynes symmetrical or unsymmetrical substituted. Under MW irradiation the consumed energy decreases considerably, the amount of used solvent also decreases (at least three-fold less comparative with conventional TH), and the reaction conditions are milder. Consequently these reactions could be considered environmentally friendly. It is also to be pointed out that under MW irradiation the yields are higher and the reaction time decreased substantially (from hours to minutes) comparative with conventional TH. A feasible explication for the MW efficiency in Huisgen [3+2] dipolar cycloaddition reactions was furnished. The regiochemistry studies indicate that the reactions occur highly regiospecific (a single regioisomer being formed), under charge control.