Ring opening reactions of N-substituted-5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxamides

Article abstract of DOI:10.1139/v82-164

The amides prepared from 5,6-dihydro-2-methyl-1,4-oxathiin-3-carbonyl chloride 2 and imidamides 4, carbamimidothioates 4, 2-benzimidazolamine 7, 2-benzothiazolamine 12, and 2-thiazolamine have been studied.The reaction of 2 with imidamides 4 and with carbamimidothioates 4 in the presence of base gave the amides 5, which when heated in toluene underwent the 1,4-oxathiin ring opening and rearrangement to produce 2-substituted-5-<(2-hydroxyethyl)thio>-6-methyl-4(1H)-pyrimidinones 6.Acylation of 2-bezimidazolamine 7 with 2 yielded the amide 10.This, in boiling ethanol, ring opened and rearrenged to give compound 11.The reaction of 2-benzothiazolamine 12 with 2 gave the rearrengement product 14 directly and neither of the possible amides 13 and 15 could be detected.The amide 15 was synthesized by an unambiguous route from 2-aminobenzenethiol and 5,6-dihydro-2-methyl-1,4-oxathiin-3-carbonyl isothiocyanate 3.It would not undergo ring opening and rearrengement when heated.Acylation of 2-thiazolamine with 2 yielded a mixture from which the amide 19 and the rearrengement ester 18 were separated.Structural assignments are based mainly on nmr, uv, and ir spectral evidence.