The synthesis of imidazo[4,5‐c] ‐ and v‐triazolo[4,5‐c] pyridazines

Abstract The parent imidazo[4,5‐c]pyridazine (IV) has been prepared for the first time by three different routes. 1‐Methylimidazo[4,5‐c]pyridazine (XX) and 3‐methylimidazo[4,5‐c]pyridazine (XXVII) have been prepared by unequivocal syntheses. The constitution of the methylation product of imidazo[4,5‐c]pyridazine‐2‐thiol (VIII) has been shown to be 2‐methylthioimidazo[4,5‐c]‐pyridazine (IX) by the unequivocal syntheses of 1‐methylimidazo[4,5‐c]pyridazine‐2‐thiol (XXIII) and 3‐methylimidazo[4,5‐c]pyridazine‐2‐thiol (XXXIII). Likewise, the structure of the methylation product (XIII) was shown to be S‐methylation by the unequivocal syntheses of 1‐methyl‐2‐methylthio‐6‐chloroimidazo[4,5‐c]pyridazine (XXIV) and 3‐methyl‐2‐methylthio‐6‐chloroimidazo[4,5‐c]pyridazine (XXXI), respectively. Several 7‐substituted amino‐v‐triazolo‐[4,5‐c]pyridazines (XXXVIII) have been prepared from 7‐chloro‐v‐triazolo[4,5‐c]pyridazine (XXXVII).