Pyrimidine ring cleavage

Heating the mesoionic l-amino-2-thioxo-l,2,4-triazolo[l,5-c]quinazo-lines 59 with aromatic aldehydes and ethanolic hydrochloric acid resulted in the formation of Schiff bases and simultaneous pyrimidine ring cleavage 

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Pyrimidine ring cleavage of l,2,4-triazolo[4,3-a]pyrimidin-7-ones (18) has been affected with bases to give the corresponding 3-amino-l,2,4-tria-... 

Hydrazinolysis of l,2,4-triazolo[4,3-a]pyrimidines (33) caused pyrimidine ring cleavage and led to the formation of the pyrazole 143 and 3-amino-1,2,4-triazole derivatives 65 (58YZ1395 62ZC369 76KGS706). A probable mechanism of this reaction is shown in Scheme 56. 

Prolonged heating of l,2,4-triazolo[4,3-c]pyrimidines (16) with water caused pyrimidine ring cleavage and afforded the 3-[l-(acylamino)-ethen-2-y 1 ]-1,2,4-triazoles 79. Compounds 79 are the acyclic intermediates... 

In acid solutions, but also in neutral solutions at high steady-state radical concentrations, the superoxide elimination becomes too slow compared with the bimolecular decay of these peroxyl radicals [reactions (28)-(31)]. This leads to a very different product distribution, as seen in Table 5. There is evidence that in their bimolecular decay peroxyl radicals can give rise to the formation of oxyl radicals which may undergo fragmentation (see, e.g., [37, 38]) [e.g., reaction (30)], leading to products with the pyrimidine cycle destroyed (e.g., l-N-formyl-5-hydroxyhydantoin. Other pyrimidine-ring cleavage reactions are conceivable but at present not supported by product data). 

Startg. m. dissolved in PCI3, kept 18 hrs. at 20°, the solvent removed under reduced pressure, and the residue dissolved in cold water -> product. Y 68%. F. e. s. J. Clark, M. Curphey, and I. W. Southon, Soc. Perkin I 1974, 1611 pyrimidine ring cleavage, review, s. J. Heterocyclic Chem. 13, S79 (1976). 

Sodium hydrogen carbonate Facile pyrimidine ring cleavage to o-aminonitriles... 

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