The Conversion of 5,5-Bi(1,2,3-dithiazolylidenes) into Isothiazolo[5,4-d]isothiazoles

Abstract

Thermolysis of 4,4-dichloro-, 4,4-diaryl-, and 4,4-di(thien-2-yl)-5,5-bi(1,2,3-dithiazol-ylidenes) affords the respective 3,6-dichloro-, 3,6-diaryl- and 3,6-di(thien-2-yl)isothiazolo[5,4-d]-isothiazoles in low to high yields. The transformation of the 4,4-diaryl- and 4,4-di(thien-2-yl)-5,5-bi(1,2,3-dithiazolylidenes) occurs at lower temperatures in the presence of the thiophiles triphenylphosphine or tetraethylammonium iodide. Optimized reaction conditions and a mechanistic rationale for the thiophile-mediated ring transformation are presented.