Rapid synthesis of tetrahydro-4H-pyrazolo[1,5-a]diazepine-2-carboxylate

Hydrazines condense with dimethyl 2-pyrrolidino-4-oxo-2-pentenedioate in the presence of aq. HCl to form N-substituted pyrazole-3,5-dicarboxylates 2. Complex bicyclic derivatives, such as pyrazolo-oxazine 3a, pyrazolo-oxazepine 3b, pyrazolo-pyrazine 4a, and pyrazolo-diazepine 4b, were generated using 2-hydrazinoethanol, 3-hydrazinopropanol, 2-hydrazinoethylamine, and 3-hydrazinopropylamine.