Straightforward green synthesis of indeno-furan carboxylates from ninhydrin and β-ketoesters: X-Ray crystal structure, Hirshfeld and DFT investigations

The diversity of the response of ninhydrin towards β-ketoesters was investigated. Indeno[1,2-b]furan-3-carboxylate 3 was obtained from ethyl acetoacetate via stirring in water for 15 min, whereas, in case of ethyl benzoylacetate afforded the 2-(2‑hydroxy-1,3-dioxo-2,3-dihydro-1H-inden-2-yl)-3-oxo-3-phenylpropanoate 2 in water for longer time about 6 h . Reaction of ninhydrin with ethyl benzoylacetate in a mixture of acetic acid/water/methanol afforded the compound 4. The different types of intermolecular interactions controlling the molecular packing of the studied crystal structures were analyzed using Hirshfeld calculations. The results shed the light on the importance of O…H, H…H and H…C interactions on the crystal stability. The minimum energy structures were predicted using DFT calculations and were found very well matched with the corresponding X-ray structures. The electronic properties HOMO, LUMO, dipole moment, MEP (molecular electrostatic potential) map and the molecular reactivity descriptors were calculated and compared. The GIAO NMR chemical shifts were calculated and the results correlated well with the experimental data and the correlation coefficients were found close to 1.