A little about Pyrazolo[3,4-d][1,2]diazepine: simple sustainable synthesis, NMR identification and prototropic equilibrium

A simple and sustainable method for the synthesis of pyrazolo [3,4-d] [1,2] diazepin-8-one, the heterocyclic isoster of 2,3-benzodiazepine, has been developed. It was found that the use of acids to cyclization of the pyrazolopyrone hydrazinolysis product leads to the formation of a condensed pyridine ring instead of 1,2-diazepine. Pyrazolodiazepinone in acidic medium also dramatically contracts the seven-membered cycle. The structure of this compound is proved by the hmbc and hsqc 2D NMR heteronuclear correlation in deuterated dimethyl sulfoxide solution in dynamic. Was studied the transformation of its tautomers. It was found that the problem for the pyrazolo [3,4-d] [1,2] diazepin-8-one molecule identification is caused by prototropic isomerization of the pyrazole ring.