The chemistry of 5-oxodihydroisoxazoles. Part 22.1 The synthesis of 1,3-oxazin-6-ones from N-thioacylisoxazol-5(2H)-ones

Abstract

N-Thioacylisoxazol-5(2H)-ones, prepared by the reaction of thiocarbonyl chlorides with isoxazol-5(2H)-ones in the presence of base, are reduced by triphenylphosphine to afford 1,3-oxazin-6-ones and triphenylphosphine sulfide. If the thioacylation is carried out with phenyl chlorodithioformate, the thermal rearrangement of the intermediate, to again form the oxazin-6-one and sulfur, is so rapid that the use of the phosphine is not required. The presence of an ethoxycarbonyl group at C-3, or of a bromine atom at C-4 of the isoxazolone results in the formation of thiazoles.