Synthesis of [1,3,5]thiadiazino[3,2-a]benzimidazole-2,4(3H)-diones and their sulphur analogues

Benzimidazol-2-yl di- or tri-thiocarbonates and iso- or isothio-cyanates give, on heating in the presence of triethylamine, the novel [1,3,5]thiadiazino[3,2-a]benzimidazole-2,4(3H)-diones (11; X = Y = O) or their sulphur analogues (11; X = S, Y = O; or X = Y = S).