Pyrimidines 1.3.5- triazines, cyano

Cyano-esters react with biguanides with results not unlike those of keto-esters. Thus, biguanide and methyl 2-cyano-4-ethyloct-3-enoate (699, 703) [CH3(CH2)3CHEt-CH=CH-CH(CN)C02Me] give a product which may be either a triazine or a pyrimidine, but a choice has so far not been... 

The most important route is the conversion of pyrimidines into 1,3,5-triazines. The first one-step transformation was effected by Taylor and Jefford (62JA3744) by heating the pyrimidine (179) with benzenesulfonyl chloride in pyridine (equation 106). The reaction may be considered as an example of an abnormal Beckmann rearrangement. The mechanism of the reaction of the 4-aminopyrimidine (180) is probably dependent on the nature of the 2-substituent (180, R). If R is an electron-releasing moiety, pathway B seems more likely (Scheme 109). The 4-hydroxypyrimidine (179 R = OH) behaves similarly. Many 2-cyano-1,3,5-triazines may be synthesized by this method. 

There are considerable data available on imidazole formation by ring contractions of pyrimidines, pyrazincs and triazines [15, 43, 59-61]. Few of the reactions, however, have synthetic potential except perhaps for the thermolytic conversions of azidopyrimidines and azidopyrazines into 1-cyano-substituled imidazoles, and the reactions of chloropyrimidines and chloropyrazines with potassium amide in liquid ammonia to give 4- and 2-cyanoimidazoles, respectively. Ring contractions of quinoxaline 1-oxides may also have some applications. 

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