A general and highly regio and stereoselective method for the synthesis of (E)-2-(2-arylvinyl)-3,1-benzoxathiin-4-ones through palladium–copper catalysis

Abstract

A palladium–copper-catalysed procedure for the synthesis of (E)-2-(2-arylvinyl)-3,1-benzoxathiin-4-ones 5a–5h is developed. 3-[2-(Methoxycarbonyl)phenylthio]propyne 2 reacts with aryl iodides 3a–3h in the presence of bis(triphenylphosphine)palladium(II) dichloride, copper(I) iodide and triethylamine in acetonitrile to furnish the disubstituted alkynes 4a–4h in good yields (70–84%). These on alkaline hydrolysis and subsequent cyclisation of the carboxylic acids formed with copper(I) iodide (20 mol%) and triethylamine in tetrahydrofuran under reflux afford (E)-2-(2-arylvinyl)-3,1-benzoxathiin-4-ones 5a–5h in 61–70% yield rather than the expected benzoxathiepinones 6. The reactions of (E)-2-(2-arylvinyl)-3,1-benzoxathiin-4-ones 5a and 5g with nucleophiles and the hydrogenation of compounds 5a, 5b and 5d are also studied.