LAUSR

Abstract We present Et3N mediated synthesis of a novel dispiro compound from 5-methyl-2-(4′-fluorophenylidine)-1-oxo-1,2,3,8-tetrahydrocyclopent[b]indole, isatin, and sarcosine through 1,3-dipolar cycloaddition reaction. The crystal structure of synthesised compound, 4′-(4-fluorophenyl)-2′,7-dimethyl-1,4-dihydro-3H-dispiro[cyclopent[b]indol-2,5′-[1,2]oxazinan-6′,3′'-indolin]-2′',3-dione is reported. FT-IR, 1H and 13C NMR chemical shifts as measured and calculated using B3LYP method with the 6-311G(d,p) basis set in gas phase were found in good agreement. The optimized geometry of the dispiro compound was compared with experimental XRD values. DFT calculations of the molecular electrostatic potential (MEP), Non-covalent interactions and Hirshfeld Surface analysis, Non-linear optical (NLO) properties and frontier molecular orbitals (FMO) identified chemically active sites of the dispiro compound responsible for its chemical reactivity.