Synthesis, crystal structure, Hirshfeld surface analysis, DFT and antihyperglycemic activity of 9-allyl-2,3,9,10a-tetrahydrobenzo[b]cyclopenta[e][1,4]diazepin-10(1H)-one

•A novel benzodiazepine-2-one derivative (4) was synthesized.•4 was characterized by FT-IR, 1H-NMR, 13C-NMR, and GC-MS.•Properties of 4 were predicted by using B3LYP/6-311++G** calculations.•Complete vibrational assignments together with the scaled force constants of 4 are reported.•4 was evaluated in vitro for their antihyperglycemic activity.