Synthesis of Isomeric Isothiazolo[4′,3′:4,5]- and Isothiazolo[4′,5′:4,5]thieno[3,2‑b]pyrano[2,3‑d]pyridines by Combination of Domino Reactions

Isothiazolothienopyridines have been prepared by a domino reaction (the SN2 reaction → the Thorpe–Ziegler reaction → the Thorpe–Guareschi reaction type) from disodium 4-cyanoisothiazole-3,5-dithiolate. By changing the order of addition of the alkylation reagents in the reaction with disodium 4-cyanoisothiazole-3,5-dithiolate both possible isomers of the isothiazolothienopyridines are synthesized. These isomers were further used in three-component domino reaction (the Knoevenagel reaction → the Michael reaction → the hetero-Thorpe–Ziegler reaction type) to obtain wide range of isomeric isothiazolothienopyranopyridines.