Tautomeric structure of dihydropyrazolo[1,5-a]-pyrimidin-7-one in a solution. A facile synthesis of novel 6-quinoxalinyldihydropyrazolo[1,5-a]pyrimidin-7-ones by ring transformation

6-Quinoxalinyldihydropyrazolo1,5-a]pyrimidin-7-ones 4a-d were synthesized by the ring transformation of 3-(N,N-dimethylcarbamoyl)furo2,3-b]quinoxaline hydrochloride 5 . Compounds 4a-d were found to exist as the 4,7-dihydro-7-oxo form E in dimethyl sulfoxide based on the nmr spectral data.