9,9′‐Thiobis‐(1,2,3,4,7,8‐hexahydro‐7‐methyl‐6 H ‐pyrimido[1,6‐ a ]pyrimidine‐6,8‐dione)

The 6‐(3‐hydroxypropylamino)‐3‐methylpyrimidine‐2,4‐dione (1) did not afford the expected 6‐(3‐chloro‐propylamino)‐ derivative on reaction with thionyl chloride, but, instead, the pyrimidine rings were joined via a sulfur bridge to give 9,9′‐thiobis(1,2,3,4,7,8‐hexahydro‐7‐melnyl‐6 H ‐pyrimido[1,6‐ a ]pyrirnidine‐6,8‐dione) ( 3 ). An identical 9,9′‐thiobis‐ derivative 3 was obtained when reacting thionyl chloride with 1,2,3,4,7,8‐hexahydro‐7‐methyl‐6 H ‐pyrimido[1,6‐ a ]pyrimidine‐6,8‐dione ( 4 ). We suppose the sulfoxide‐ derivative 2 to be the intermediate of both routes: it underwent reduction to the final sulfide 3 in excess thionyl chloride.