Azo dienophiles. Diels–Alder reactions of 4-phenyl-1,2,4-triazole-3,5-dione and 5-phenylpyrazol-3-one with functionalised dienes

Abstract

4-Phenyl-1,2,4-triazole-3,5-dione (PTAD) undergoes a Diels-Alder reaction with a variety of functionalised dienes. The adduct (9) from 2,3-bis(iodomethyl)butadiene gives, on treatment with zinc–copper couple, the diene 2,3,5,6,7,8-hexahydro-6,7-dimethylene-2-phenyl-1H-[1,2,4]triazolo[1,2-a]-pyridazine-1,3-dione (10) which then reacts with dienophiles in a tandem Diels-Alder reaction. The unsymmetrical azo dienophile, 5-phenylpyrazol-3-one (3), reacts regioselectively with 1-acetoxy-butadiene to give, after hydrolysis, the alcohol 5,8-dihydro-8-hydroxy-3-phenyl-1H-pyrazolo[1,2-a]-pyridazin-1-one (19).