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

The parent imidazo4,5-c]pyridazine (IV) has been prepared for the first time by three different routes. 1-Methylimidazo4,5-c]pyridazine (XX) and 3-methylimidazo4,5-c]pyridazine (XXVII) have been prepared by unequivocal syntheses. The constitution of the methylation product of imidazo4,5-c]pyridazine-2-thiol (VIII) has been shown to be 2-methylthioimidazo4,5-c]-pyridazine (IX) by the unequivocal syntheses of 1-methylimidazo4,5-c]pyridazine-2-thiol (XXIII) and 3-methylimidazo4,5-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-chloroimidazo4,5-c]pyridazine (XXIV) and 3-methyl-2-methylthio-6-chloroimidazo4,5-c]pyridazine (XXXI), respectively. Several 7-substituted amino-v-triazolo-4,5-c]pyridazines (XXXVIII) have been prepared from 7-chloro-v-triazolo4,5-c]pyridazine (XXXVII).