A study of factors leading to N, N-diacetylation of aminopyrimidines Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/gb19f810n

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  • Although 4- and 5-diacetamidopyrimidines have been reported in the literature within the past eleven years, it was not until 1965 that a 2-diacetamidopyrimidine was reported. The current investigation was undertaken to determine whether other 2-diacetamidopyrimi-dines could be synthesized and what the effect of various nuclear substituents would be on the course of the reaction. The new compounds 2-diacetamido- and 2-diacetamido-4, 6-dimethyl-pyrimidine were synthesized. In the acetylation attempts of 2-amino-4, 6-dihydroxy- and 2-amino-4, 6-dichloro-pyrimidines and 6-aminouracil under identical conditions used for diacetylation of the three 2-aminopyrimidines, no acetylation product at all could be isolated. With 2-methoxy-4-amino- and 6-amino-2, 4-dichloropyrimidine only a monoacetamido derivative was formed and isolated. The former is a new compound. 5-Diacetamido-4, 6-dichloropyrimidine, previously prepared by isopropenyl acetate, was prepared in lower yield under the above conditions. Therefore, it would seem that m-positioned electron-donating groups (in the 5-aminopyrimidines the ring nitrogens are so positioned) enhance the nucleophilicity of an aminopyrimidine and that similarly positioned electron-withdrawing groups reduce the nucleophilicity of the amine. The most striking feature that was noticed when the known diacetamido pyrimidines were compared is that almost every one (with the exception of the three 2-diacetamidopyrimidines, which have the ring nitrogens in the ortho position) was substituted in at least one ortho position. That diortho substituents hinder monoacetylation of anilines but greatly enhance the probability and yield of diacetanilides was first observed nearly a century ago. A similar facilitating effect of ortho substitution in the acylation of aminopyridines has also been observed. Since the effect of ortho substituents on an aromatic nucleus in ester or amide hydrolysis is one of hindrance, it was puzzling that steric facilitation seemed to be operative in diacetamide formation. An attempt has been made here to correlate what has been reported regarding the syntheses of N-aryl diacetamides, to make some generalizations regarding the factors necessary for the achievement of diacylation of such compounds, and to draw some conclusions with respect to the probable reasons for the behavior observed. The infrared and ultraviolet spectra of the diacetamides prepared in this investigation and the behavior of these compounds when chromatographed on silica gel or alumina thin layer plates are described. An unsuccessful attempt to synthesize 4-amino-2-methyl pyrimidine via reaction between acetamidine hydrochloride and the sodium enolate of cyanoacetaldehyde is reported.
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