Versatile synthesis and fungicidal activities of 6-amino-3alkylthio-1,5-dihydro-1-phenyl-pyrazolo [3,4-d]pyrimidin-4-one derivatives

A series of new 6-alkylamino-3-alkylthio-1-phenyl-1H-pyrazolol[3,4-d] pyrimidin-4(5H)-one derivatives 5 and 6 have been rapidly synthesized by a novel solution-phase regioselective synthetic method. Treatment of pyrazole o-aminoester 1 with dibromotriphenylphosphorane gave iminophosphorane 2, which underwent a aza-Wittig reaction with phenyl ioscyanate to provide the carbodiimide 3. The latter intermediate reacted with alkylamines and regioselectively provided the 1,5-dihydro-pyrazolo[3,4-d]pyrimidin-4-one derivatives 5 and 6, some of which exhibited good fungicidal activity.