Base-catalysed ring opening of N-(aminothioxomethyl)-5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxamides

The condensation of 5,6-dihydro-2-methyl-1,4-oxathiin-3-carbonyl isothiocyanate (1) with ethyl 3-phenylamino-2-butenoate (2) has yielded a mixture of ethyl 1,4-dihydro-2-(5,6-dihydro-2-methyl-1, 4-oxathiin-3-yl)-6-methyl-1-phenyl-4-thioxo-5-pyrimidine carboxylate (3) and N-[(phenylamino)thioxomethyl]-5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxamide (4, R′ = phenyl). It has been discovered that compounds 4, in general, rearrange to 1-substituted-2,3-dihydro-5-[(2-hydroxyethyl)thio]-6-methyl-2-thioxo-4(1H)-pyrimidinones (5) at room temperature when stirred with dilute aqueous sodium hydroxide. The products of the reaction of 5,6-dihydro-2-methyl-1,4-oxathiin-3-carbonyl isothiocyanate (1) and phenylhydrazine, when treated with dilute aqueous sodium hydroxide, did not yield the rearrangement product 5 (R′ = NHC6H5). Instead, a mixture of the two triazole-3-thiones 9 and 10 was formed. N,2-Bis(5,6-dihydro-2-methyl-1,4-oxathiin-3-carbonyl)hydrazinecarbothioamide (12) with dilute aqueous sodium hydroxide yielded one rearrangement product (out of a possible four), namely, 5-6-dihydro-2-methyl-N-[1,2,3,4-tetrahydro-5-[(2-hydroxyethyl)thio]-6-methyl-4-oxo-2-thioxo-1-pyrimidinyl]-1,4-oxathiin-3-carboxamide (13).