Diastereoselective [5+1] double Michael reactions of thiooxindole with divinyl ketones: Synthesis of meso-spiro[cyclohexanone indoline-2-thione] by intramolecular induction with sulfur

The first diastereoselective synthesis of spiro-thiooxindole is reported via Michael reaction between thiooxindoles and divinyl ketones. The reaction was conducted without any catalyst or additive in ethanol as a green solvent at room temperature. This study showed the art of governing regioselectivity in which novel spiro frameworks were generated in high yields. In addition, simple purification process and diastereoselectivity make this protocol highly attractive. The structure of the products was investigated in the light of spectral data (IR, HRMS, 1H-NMR, 13C-NMR, NOESY, COSY, and X-ray diffraction). These compounds can be active biological substances and worthy of attention for the medicinal chemists.