Vk. Ahluwalia et al., A CONVENIENT ONE-POT SYNTHESIS OF TETRAHYDRO-10H-PYRIMIDO[5,4-B][1,4]-BENZOTHIAZINES, Indian journal of chemistry. Sect. B: organic chemistry, including medical chemistry, 33(1), 1994, pp. 65-66
The reaction of 1,3-dimethylbarbituric acid (1) with N-bromosuccinimid
e followed by condensation with o-aminothiophenols (2a-d) results in t
he formation of 1,3-dimethyl-2, 4-dioxo-1, 2, 3, tetrahydro-10H-pyri-m
ido[5,4-b][1,4]benzothiazines (3a-d). Further, N-alkylation of 3a-d wi
th formaldehyde and piperidine gives the corresponding 1,3-dimethyl-2,
4-dioxo-10-(N-piperidmomethyl-1, 2, 3, -tetrahydro-10H-pyrimido[5,4-b]
[1,4]benzothiazines (4a-d).