9,9 '-thiobis-(1,2,3,4,7,8-hexahydro-7-methyl-6H-pyrimido[1,6-a]pyrimidine-6,8-dione)

The 6-(3-hydroxypropylamino)-3-methylpyrimidine-2,4-dione (1) did not affor d the expected 6-(3-chloropropylamino)- derivative on reaction with thionyl chloride, but, instead, the pyrimidine rings were joined via a sulfur brid ge to give 9,9'-thiobis(1,2,3,4,7,8-hexahydro-7-methyl-6H-pyrimido[1,6-a]py rimidine-6,8-dione) (3) An identical 9,9'-thiobis- derivative 3 was obtaine d when reacting thionyl chloride with 1,2,3,4,7,8-hexahydro-7-methyl-6H-pyr imido[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 fina l sulfide 3 in excess thionyl chloride.