THE CHEMISTRY OF 5-OXODIHYDROISOXAZOLES - PART 22 - THE SYNTHESIS OF 1,3-OXAZIN-6-ONES FROM N-THIOACYLISOXAZOL-5(2H)-ONES

N-Thioacylisoxazol-5(2H)-ones, prepared by the reaction of thiocarbony l chlorides with isoxazol-5(2H)-ones in the presence of base, are redu ced by triphenylphosphine to afford 1,3-oxazin-6-ones and triphenylpho sphine sulfide. If the thioacylation is carried out with phenyl chloro dithioformate, the thermal rearrangement of the intermediate, to again form the oxazin-6-one and sulfur, is so rapid that the use of the pho sphine 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 format ion of thiazoles.