The photochemical synthesis of novel heterocyclic compounds from s ‐triazolo[4,3‐ b ]pyridazine (II)

s ‐Triazolo[4,3‐ b Jpyridazine (I) photochemically reacted with dihydropyran; 2,3‐dihydro‐ p ‐dioxin; 2,5‐dihydrofuran; 2,5‐dimethoxy‐2,5‐dihydrofuran; and 1,3‐dioxep‐5‐ene to give a new series of substituted pyrrolo[1,2‐ b ]‐.s‐triazoles (II‐IX). In most reactions, two or more products were formed. The following compounds have been prepared from I: 9‐methylene‐4a,5,6,7,8a,9‐hexahydropyrano[2,3 :4,5]pyrrolo[1,2‐ b ]‐ s ‐triazole (Ha), the corresponding 9‐cyanomethyl product (III), and 9‐methylene‐4a,7,8,8a‐tetrahydro‐6 H ,9 H ‐pyrano[3′,2′:4,5]pyrrolo[1,2‐ b ]‐ s ‐triazole (IIb) from dihydropyran; 9‐methylene‐4a,6,7,8a‐tetrahydro‐9 H‐p ‐dioxino[2′,3′:4,5]‐pyrrolo[1,2‐6]‐s‐triazole (IV) from 2,3‐dihydro‐ p ‐dioxin; 8‐methylene‐4a,5,7a,8‐tetrahydro‐7 H ‐furo[3′,4′:4,5]pyrrolo[1,2‐ b ]‐ s ‐triazole (V) and the corresponding 8‐cyanomethyl product (VI) from 2,5‐dihydrofuran; 8‐cyanomethyl‐5,7‐dimethoxy‐4a,5,7a,8‐tetrahydro‐7 H ‐furo[3′,4′:4,5]‐pyrrolo[1,2‐6]‐ s ‐lriazole (VII) from 2,5‐dimethoxy‐2,5‐dihydrofuran; and 10‐methylene‐4a,5,9a,10‐tetrahydro‐9 H ‐[1,3]dioxepino[5′,6′:4,5]pyrrolo[1,2‐ b ]‐ s ‐triazole (VIII) and the corresponding 10‐cyanomethyl product (IX) from 1,3‐dioxep‐5‐ene. The addition of several other compounds (1,2,3,6‐tetrahydropyridine, 1‐acetylimidazole, 3‐sulfolene, 2,3‐dihydro‐ p ‐dithiin, and vinylene carbonate) was attempted, but no reactions were observed.