Pyrimidines formation

Extension of this work by studying the reaction of 3-methyl-5-nitro-pyrimidin-4(3//)-one with -X-arylketones in the presence of ammonium acetate surprisingly revealed the formation of a mixture of 4-arylpyrimidines and 6-arylpyridin-2(l//)-ones (00JCS(P1)27). The ratio between pyridine and pyrimidine formation is dependent on the substituent X. With electron-donating substituents the formation of the pyridin-2(l//)-ones is favored, with electron-attracting substituents the formation of the pyrimidine derivatives (Scheme 21) In the formation of the 6-arylpyridin-2(l//)-ones the C-4- C-5-C-6 part of the pyrimidone-4 is the building block in the construction of the pyridine ring. Therefore, the pyrimidone can be considered as an activated o -nitroformylacetic acid (Scheme 21). 

Diaminopyrimidine is reported to react with triphenylphosphite to give 1,3,2-diazaphos-pholo[l,5-. In both cases, however, the physical properties of the isolated materials are in accord with oligomers rather than with monomeric azaphospholes. 

Since allopurinol blocks xanthine conversion to uric acid, urinary xanthine excretion is increased, creating a risk of xanthine crystal formation in the urinary system or even in muscles this can result in nephrolithiasis (12). It is still an open question whether a predisposition to renal disease or renal disease itself is required to precipitate these adverse effects. It is also not known whether increased excretion of orotic acid, due to an interaction of allopurinol with pyrimidine formation, has any consequences for these adverse effects or for its role in reducing glucose tolerance. 

Substituents in a 1,4-quinone may be displaced by nucleophiles in the presence of strong bases an amidine supplies the necessary atoms for pyrimidine formation. When the amino and carbonyl functions are in peri positions, a doubly fused ring is formed by reaction with formamide. 

Pyrrolidine enamines 4 can undergo a regiospecific cycloaddition with 1,3,5-triazine (la). In each case, pyrimidine formation occurs under mild conditions (45-90°C) with dioxane being the most effective solvent.2-3... 

It is thought that pyrimidine formation is a two-step process including acylation of the imino enamine and further dehydration of this intermediate acyl derivative leading to ring closure. 

Oxazines and 1,3-thiazines have been used quite extensively as substrates in pyrimidine syntheses (B-94MI 602-0l>. 1,3-Thiazines are intermediate structures in several cyclization reactions involving thioxo substrates. Pyrimidine formation from thiazines may involve a Dimroth-like rearrangement of a thiazinamine, an aminolytic displacement of the ring sulfur atom, or a combination of both. Aqueous ethanol in methylamine converts 4-phenyl-5-phenylsulfonyl-2//-l,3-thiazine-2,6(3//)-dithione (589) into the pyrimidine (590) by displacement of the ring sulfur and a nucleophilic substitution of the thioxo sulfur in the 2-position (Scheme 93) (88JHC835). 

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