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Triethylammonium 5-[(1,3-dimethyl-2,4,6-trioxo-tetrahydropyrimidin-5(6H)-ylidene)-(methylthio) methyl]-1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4-olate (5), obtained from 5-[bis (methylthio)methylene]-1,3-dimethyl-2,4,6(1H,3H,5H)-pyrimidinetrione (2) and 1,3-dimethylbarbituric acid in the presence of triethylamine, is protonated by methanesulfonic acid to give 5,5ʹ-(methylthiomethanediylidene)bis(1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione) (6) in good yield. Compound 6 is oxidized in two steps by m-chloroperbenzoic acid to give 5,5ʹ- (methylsulfinylmethanediylidene)bis(1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione) (7) and 5-[(1,3-dimethyl-2,4,6-trioxo-tetrahydropyrimidin-5(6H)-ylidene)(methylsulfinyl)methyl]-5-hydroxy- 1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione (8), respectively. Excess pyridine eliminates methanesulfinic acid from 8 to give the zwitterionic 5-[(1,3-dimethyl-2,4,6-trioxo-tetrahydropyrimidin- 5(6H)-ylidene(pyridinium-1-yl)methyl]-1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydropyrimidin- 4-olate (9). The crystal structures of compounds 6, 8, and 9 are reported.

Elimination of a Thiomethyl Substituent from an Anionic 5-Methylenebarbituric Acid Derivative by Oxidation and Substitution