Heterocyclic studies. Part XIII. Ready ring cleavage of some pyrimidine derivatives to give highly substituted ethylenes

Treatment of 6-chloro-4-dialkylamino-5-nitropyrimidines (Ia–d) under acidic conditions resulted in ring cleavage and formation of 3-amino-3-dialkylamino-2-nitroacrylonitriles (IIIa–d). Similar treatment of 4-amino- or 4-alkylamino-6-chloro-5-nitropyrimidines also gave acrylonitriles (IIIe–i) but 4-amino- or 4-alkylamino-5-nitropyrimidin-6(1H)-ones (IIe–i) were formed at the same time.The relative proportions of ring cleavage and simple nucleophilic substitution varied with the 4-substituent and with the pH. Under near neutral conditions only the pyrimidinone (II) was formed, even when the 4-substituent was dialkylamino. 1 H N.m.r., u.v., and i.r. spectra are tabulated.