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A general approach towards the synthesis of tetrahydro-4 H -pyrazolo[1,5- a ][1,4]diazepin-4-one, tetrahydro[1,4]diazepino[1,2- a ]indol-1-one and tetrahydro-1 H -benzo[4,5]imidazo[1,2- a ][1,4]diazepin-1-one derivatives was introduced. A regioselective strategy was developed for synthesizing ethyl 1-(oxiran-2-ylmethyl)-1 H -pyrazole-5-carboxylates from easily accessible 3(5)-aryl- or methyl-1 H -pyrazole-5(3)-carboxylates. Obtained intermediates were further treated with amines resulting in oxirane ring-opening and direct cyclisation-yielding target pyrazolo[1,5- a ][1,4]diazepin-4-ones. A straightforward two-step synthetic approach was applied to expand the current study and successfully functionalize ethyl 1 H -indole- and ethyl 1 H -benzo[ d ]imidazole-2-carboxylates. The structures of fused heterocyclic compounds were confirmed by 1 H, 13 C, and 15 N-NMR spectroscopy and HRMS investigation.