4-monosubstituted pyrimidines

Methyl ketones give 4-monosubstituted-pyrimidines when reacted with formamide at high temperature. Although the yields, apart from aryl-methyl-ketones, are not large, the method is extremely simple. Aryl higher-alkyl ketones also react in this way, giving 4-aryl-5-alkyl-pyrimidines. 

Tetrahydroquinazolines are more conveniently classified as 4,5-tetramethylene pyrimidines and their reactions are accordingly typical of pyrimidines. 2,4-Disubstituted derivatives have been prepared by condensation of 1-ethoxycarbonyl cyclohexanones with ureas and thioureas (Scheme 9). For monosubstituted derivatives the... 

Addition of nucleophiles to the cyano group of cyanothiadiazole under basic conditions takes place with unusual ease <88AG(E)434,94ACS372). Hydrolysis to the amide, for example, can be effected at 0°C in the presence of a catalytic amount of sodium hydroxide or basic ion-exchange resin. At reflux temperature, hydrazine and monosubstituted hydrazines convert 3,4-dicyano-l,2,5-thia-diazole into the l,2,5-thiadiazole[3,4-. The base-catalyzed addition of acetone to cyanothiadiazole forms an enamino ketone, used as a key intermediate for the synthesis of a number of heterocyclic ring systems, e.g. isothiazole, isoxazole, pyrazole, pyrimidine, and thiazole <77H(6)1985>. 

Four ring-stretching modes for pyridines and pyrimidines are listed in Table 20, together with the corresponding bands of a monosubstituted benzene. Quinolines and isoquinolines show seven or eight bands in the region 1650-1350 cm-1. 

Table 3.10. One-, Two-, Three-, and Four-Bond Carbon-Proton Coupling Constants (Hz) of Benzene (a), Pyridine (b), Pyrimidine (c), Monosubstituted Benzenes [128] (d) and Five-Membered Heteroaromatics [130] (e).

From 2-amino-6-methylpyridine and monosubstituted malonates Buu Hoi and Declerq100 obtained 3-substituted 1,8-naphthyridines of type 66, and from 2-aminopyridine they obtained 3-substituted pyrido[l,2- ]pyrimidines of type 63 (R = H). 

Dvortsak et al.117 found that bis(pentachlorophenyl)malonates and 2-aminopyridine formed the pyrido[l,2-a]pyrimidines (63 R = H) even at room temperature in acetone in the presence of triethylamine. By the reaction of bis(2,4,6-trichlorophenyl)malonates with 2-(monosubstituted amino)pyridines at 160-175rC, the 1-substituted derivatives of the pyrido[l,2-a]pyrimidines (63) were prepared.114-116... 

Monosubstituted amino)pyridine and carbon suboxide in ether furnished 1-substituted derivatives of pyrido[l,2- ]pyrimidines (63).115 22123 With aluminum chloride as a catalyst, yields were almost quantitative.122... 

After the nucleophilic aromatic substitution of pyrimidine 123, the isolated monosubstituted ether product 124 was cyclized with paraformaldehyde in dichloromethane under acidic Pictet-Spengler conditions to form pyri-mido[4.5-/+1.4- benzoxazcpinc 125 in good yield (62%) (Scheme 15) <2005JOC9629>. The same procedure has... 

Since D-hydantoinase was identified as dihydropyrimidinase, it is proposed that D-amino acid production from DL-5-monosubstituted hydantoins involves the action of the series of enzymes involved in the pyrimidine degradation pathway. Based on this proposal, D-decarbamoylase was thought to be identical with P-ureidopropionase (EC 3.5.1.6) which functions in pyrimidine metabolism. 

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