Meso-ionic compounds. Part 12. Synthesis of 1-alkyl-4-oxopyrimido-[1,2-a]-S-triaziniumolates and their 4-thio-derivatives

Abstract

Treatment of 2-alkylaminopyrimidines (1) and (2) with ethoxycarbonyl isocyanate gave the acyclic urea derivatives, namely, 3-alkyl-1-ethyoxycarbonyl-3-(2-pyrimidyl)ureas (3) and (4), which cyclized to 1-alkyl-4-oxopyrimido-[1,2-a]-s-triazin-1-ium-2-olates (6) and (7) in refluxing p-xylene. Structural proof was obtained through spectral analyses, and an alternate synthesis in which (1) and (2) were reacted with phenoxycarbonyl isocyanate.

Reaction of (1) and (2) with ethoxycarbonyl isothiocyanate gave 2-alkylimino-1 (N-ethoxycarbonylthiocarbamoyl)-1,2-dihydropyrimidines (8) and (9) which on treatment with trifluoroacetic acid cyclized to 1-alkyl-4-thioxopyrimido [1,2-a]-s-triazin-1-ium-2-olates (10) and (11), respectively. similar reactions of (1) with phenoxycarbonyl isothiocyanate did not yield either the precursor (8), the carbonyl isothiocyanate (12), or the expected maso-ionic system, 1-methyl-2-thioxopyrimido [1,2-a]-s-triazin-1-ium-4-olate (13).

The insolubility and instability of (10) and (11) made purification extremely difficult, and consequently structural characterization was based on spectral analyses.

The reaction of ethylamine with (6) and (10) gave products for which the 1-alkyl-6-amino-1,2,3,4-tetrahydro-s-triazine structures (14) and (16), respectively, were assigned based on mass spectral analyses.