Heterocyclic studies. Part XXXII. Some 5H-pyrimido[4,5-b][1,4]thiazin-6(7H)-ones

Abstract

Condensation of 6-(substituted amino)-5-aminopyrimidine-4(3H)-thiones with chloroacetic acid (or its ethyl ester), ethyl bromomalonate, or ethyl α-bromopropionate yielded 4-(substituted amino)-5H-pyrimido[4,5-b][1,4]-thiazin-6(7H)-ones with no substituent, an ethoxycarbonyl group, or a methyl group, respectively, in the 7-position. Some of the compounds were converted into 5-methyl, 5-benzyl, or 5-allyl derivatives. ¹H N.m.r., u.v., and i.r. spectroscopy showed that the pyrimidothiazines were 5H-6(7H)-ones rather than other possible tautomers. Ionisation of the compounds is discussed and mass spectra are recorded and discussed.