Pyrimidine derivatives and related compounds. Part 41. Reactions of 1,3,6-trimethyl-5-nitrouracil and its 6-bromomethyl analogue with amines and hydrazines. Synthesis of pyrazolo[4,3-d]pyrimidine N-oxides and their ring expansion to pyrimido[5,4-d]pyrimidines

Abstract

Reactions of 1,3,6-trimethyl-5-nitrouracil (1) and 6-bromomethyl-1,3-dimethyl-5-nitrouracil (4) with amines and hydrazines have been studied with the aim of synthesising fused-ring pyrimidines. Treatment of compound (4) with primary amines afforded 2-substituted pyrazolo[4.3-d]pyrimidine 1-oxides (6a–I). Of these, compounds (6h–I) were converted into pyrimido[5,4-d]pyrimidines (11) by treatment with sodium ethoxide. Although treatment of compound (1) with hydrazines caused the known ring transformation giving pyrazolones (2a and b), a new type of denitration reaction was found when compound (4) reacted with hydrazines yielding 6-hydrazonomethyl-1,3-dimethyluracils (15a and b). Treatment of the 6-(substituted methyl)-1,3-dimethyl-5-nitrouracils (13b–d) and (14)[prepared from (4)] with hydrazines also gave (15a and b). Mechanisms for the formation of compounds (6), (11), and (15) are discussed.