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

A palladium-copper-catalysed procedure for the synthesis of (E)-2-(2-arylvi nyl)-3,1-benzoxathiin-4-ones 5a-5h is developed. 3-[2-(Methoxycarbonyl)phen ylthio]propyne 2 reacts with aryl iodides 3a-3h in the presence of bis(trip henylphosphine)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 ca rboxylic 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. T he 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 stud ied.