An efficient hetero Diels-Alder approach to imidazo[4,5-c]pyridazines as purine analogues

Article abstract of DOI:10.1016/S0040-4039(98)00806-5

A general approach to 3-deaza-6-azapurine by a hetero Diels-Alder reaction is described. Reaction of sulfonamide protected 5-vinylimidazole with 4-phenyl-1,2,4-triazoline-3,5-dione in methanol gave the Diels-Alder adduct 8 in 85% yield. Deprotection of the resulting N-phenyltriazole was efficiently accomplished by ring opening with hydrazine followed by heating in DMSO. The completely deprotected and aromatized purine analogue 1 was obtained directly from this one-pot reaction in 48% yield.