[3+2] Cycloaddition Reaction for the Stereoselective Synthesis of a New Spirooxindole Compound Grafted Imidazo[2,1-b]thiazole Scaffold : Crystal Structure and Computational Study

Abstract

A new spirooxindole hybrid engrafted imidazo[2,1-b]thiazole core structure was designed and achieved via [3+2] cycloaddition reaction approach. One multi-component reaction between the ethylene derivative based imidazo[2,1-b]thiazole scaffold with 6-Cl-isatin and the secondary amine under heat conditions afforded the desired compound in a stereoselective manner. The relative absolute configuration was assigned based on single-crystal X-ray diffraction analysis. Hirshfeld calculations for 4 revealed the importance of the H . . . H (36.8%), H . . . C (22.9%), Cl . . . H (10.4%) and S . . . H (6.6%), as well as the O . . . H (4.7%), N . . . H (5.3%), Cl . . . C (1.6%), Cl . . . O (1.0%) and N . . . O (0.5%) contacts in the crystal stability. DFT calculations showed excellent straight-line correlations (R2 = 0.9776–0.9962) between the calculated and experimental geometric parameters. The compound has polar nature (3.1664 Debye). TD-DFT and GIAO calculations were used to assign and correlate the experimental UV-Vis and NMR spectra, respectively.