Preparation of 2-arylmethylene-5-methylbenzo[b]thiophen-3(2H)-one 1-oxides, 1,1-dioxides, spiroepoxides, 1-oxide spiroepoxides and 1,1-dioxide spiroepoxides

Abstract

2-Arylmethylene-5-methylbenzo[b]thiophen-3(2H)-one (thioaurones) were selectively oxidised by electrophilic reagents at the sulphur atom to give the 1-oxide or 1,1-dioxide derivatives, or at the olefinic bond by nucleophilic reagents to give the spiroepoxide derivatives. Aqueous sodium hypochlorite adjusted to various pHs was found to be a versatile reagent for the controlled oxidation of thioaurones to the spiroepoxide, sulphoxide, and isomeric sulphoxide spiroepoxide derivatives. The thioaurone spiroepoxide (6a) was oxidised using hypochlorous acid or m-chloroperbenzoic acid, and thioaurone sulphoxide (3a) was epoxidised with sodium hypochlorite or alkaline hydrogen peroxide into the isomeric sulphoxide spiroepoxide derivatives. The 1,1-dioxide spiroepoxide (11) was obtained on epoxidation of the dioxide (4a).