Pyrimido [4,5-e][1,3,4]thiadiazines have the ditinct biological activities which promoted us to make an unused method and derivatives for the synthesis of them. These compounds have the potential of being nucleoside analogues, [1,2] phosphodiesterase inhibitor[3] and diuretic, anti-inflammatory and hypotensive agents [3,4]. The synthetic routes are limited and there are just a few procedures for synthesis of these compounds [4-8]. In pursuing our interest in the synthesis of this class of heterocycles, 5-bromo- 2-chloro-6-methyl-4-(1-methylhydrazino)pyrimidine (2) was prepared from the reaction of 5-bromo-2,4-dichloro-6-methyl pyrimidine (1) with methyl hydrazine. The one-pot heterocyclization of compound (2) with various aromatic isothiocyanates afforded the new derivatives of pyrimido[4,5-e][1,3,4] thiadiazines 3a-h as brownish needles. The structures of these compounds were confirmed from their spectral and micro analytical data.

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