5-羟基嘧啶——Ⅴ.1,3-二甲氧基乙酰丙酮与胍和硫脲的缩合

5-Hydroxypyrimidines——V.Condensation of 1,3-Dimethoxyacetylacetone with Guanidine and with Thiourea

1,3-二甲氧基乙酰丙酮(1)与胍在中性条件下以低产率(28%)缩合生成5-甲氧基-2-氨基-6-甲氧甲基-4-甲基嘧啶(3),而不与硫脲缩合。在与S-甲基异硫脲的反应中,1降解为甲氧基丙酮和甲氧基乙酸,从而生成甲氧基丙酮缩-S-甲基异硫脲甲氧基乙酸盐(4)和S-甲基异硫脲甲氧基乙酸盐(5)。由此可见,1对碱非常敏感,而对酸有一定的稳定性。

1,3-Dimethoxyacetylacetone (1) is shown to be sensitive to alkali whichprevents its condensation to form pyrimidines.1 under practically neutral condition con-denses sluggishly with guanidine carbonate to give only 28% yield of 2-amino-5-methoxy-6-methoxyme thyl-4-methylpyrimidine (3).1 does not react smoothly with urea andwith thiourea;with S-methylisothiourea in the presence of sodium methoxide,the reac-tion products are N-methoxyisopropylidene S-methylisothiourea methoxyacetate (4) andS-methylisothiourea methoxyacetate (5).When S-benzylisothiourea is used,the onlyproduct is the benzyl analog of 5.