Nitration of some 2-substituted-1,4,5,6-tetrahydro-pyrimidine-4,6-diones gave several new 2-substituted-1,4,5,6-tetrahydro-5,5-gem-dinitropyrimidine-4,6-diones (3) in high yields (＞80%). The gem- dinitro products formed were easily attacked by nucleophiles with the formation of gem-dinitroacetyl derivatives, which in turn could be further hydrolyzed to the salts of dinitromethane. When the substituent at position 2 was an alkyl group, the nitration occurred both at position 5 and α-carbon atom of the side chain. If the alkyl group was methyl, the product would be 2-(dinitromethylene)-5,5-dinitropyrimidine-4,6-dione (1), which was hydrolyzed to form 1,1-diamino-2,2-dinitroethylene (FOX-7) and dinitromethane (2). When the substituent was hy-droxyl, the nitrated product was 5,5-dinitrobarbituric acid (7b), which was hydrolyzed to form gem-dinitroacetylurea (9b). 9b reacted with KOH to form potassium gem-dinitroacetylurea (10b) and potassium dinitromethane (11). When the substituent was amino, gem-dinitroacetylguanidine (9a) could be synthesized by hydrolytic cleavage of nitrated product. 9a reacted with KOH to form potassium gem-dinitroacetylguanidine (10a) and 11. When there was no substituent at position 2, 7c with its structure being postulated was obtained. The effect of different nucleophiles on yield of FOX-7 was compared. Three different synthetic routes to FOX-7 were appraised. The reaction mechanism was discussed.

Key words: nitration, 2-substituted-1,4,5,6-tetrahydro-5,5-gem-dinitropyrimidine-4,6-dione, reaction mechanism, ring cleavage, potassium dinitromethane, 1,1-diamino-2,2-dinitroethylene (FOX-7)