DFT Studied Hetero‐Diels–Alder Cycloaddition for the Domino Synthesis of Spiroheterocycles Fused to Benzothiazole and Chromene/Pyrimidine Rings in Aqueous Media

Structurally diverse spiroheterocycles; spiro[pyrimido[2,1-b]benzothiazole-3,3'-chromene]-2',4'-dione, spiro[pyrimido[2,1-b]benzothiazole-3,5'-pyrimidine]-2',4',6'-trione, and spiro[pyrimido[2,1-b]benz-thiazole-3,2'-cyclohexane]-1',3'-dione have been synthesized by an environmentally benign, efficient, and facile one-pot pseudo-four component reaction of 2-aminobenzothiazoles with aromatic aldehydes and cyclic beta-diketones in aqueous medium. The process involves hetero-Diels-Alder cycloaddition and provides facile access to spiroheterocycles fused with potentially interesting biologically active scaffolds. The configuration of hetero-Diels-Alder cycloadduct has been ascertained through density functional theory calculations.