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Adducts of the available ylide Ph 3 P-CHCN with acylisocyanates and their thio analogues undergo facile cyclization, promoted by hydrogen chloride in methanol, to give high yields of 2-alkyl(aryl)-4-hydroxy(mercapto)-6-oxo-1,6-dihydropyrimidin-5-yl-triphenyl- phosphonium chlorides suitable to prepare several types of phosphonium ylide-betaines of the pyrimidine series, the structure of which...
The combined chemical, spectral, and X-ray structural investigation has shown that the structure and properties of mesomeric triphenylphosphonium ylides containing the 5-oxo-2-phenyl-4-oxazolidene moiety undergo considerable changes when the carbonyl oxygen atom is replaced by sulfur or selenium. This substitution leads to a clear decrease of the contribution of the ylide structure and an increased...