Oxopyrimidine

The equilibrium between the amino and imino forms of cytosine has also been studied by Cieplak et al.9 Their results agree with those of Colominas et al. In this study, the related 2-oxopyridine and 2-oxopyrimidine molecules were also treated. In both these molecules the amine group of cytosine is not present, and in oxopyridine only one ring nitrogen is present. This enabled the keto-imino tautomerism to be studied in isolation. In both cases the imino form dominates in the gas phase, but the keto form is stabilised by solvation, and dominates in solution, in agreement with experiment. 

Similar considerations were used60,96 to rule out the zwitterionic structure of cytosine as its main form in aqueous solution. As a zwitterion (10) cytosine ought to have a spectrum similar to that of the anion of 2-oxopyrimidine. The differences between the spectra of the two compounds indicate that this is not the case. 

A 13C—NMR study of several dimethylamino derivatives of pyridine, pyrimidine, and 2-oxopyrimidine with and without o-methyl substitution indicates a progressive twist of the dimethylamino group in hindered derivatives (78JCS(P2)1119). Unfortunately, the barriers have not yet been determined. The free energy of activation for 4-(Af-methylamino)pyridine (80JCS(P2)1704) is AG = 42.6 kJ mol-1 and is close to that of N-methyl-4-nitroaniline. 

The foregoing and, in particular, the reactivity of the 2-oxopyrimidine radical in DMSO, is relevant to the mechanism of photooxidation of the 2-oxopyrimidine dimer to the monomer on irradiation at 254 nm in DMSO 83). The initial step in the latter process would be the formation of a protonated neutral free radical, RH). which is rapidly oxidized (—0.8 V) to RH), followed by deprotonation. 

Since 4-aminopyrimidine is known to exist predominantly in the amino form, with a double bond between N(3) and C(4), it bears some structural resemblance to adenine, which may be considered a formal analogue of a 5,6-disubstituted 4-aminopyrimidine, and (at least to some extent) of cytosine, which is 4-amino-2-oxopyrimidine (Table II). This pointed to the possible utility of a detailed examination of the electrochemical behaviour of 4-aminopyrimidine, and some of its methylated analogues. 

The photodissociation of the 2-thiopyrimidine dihydrodimers, Dt 3 (Scheme 21) is really a photooxidation process since, formally, the observed products, the parent 2-thiopyrimidines, are regenerated by removal. of two electrons and two protons. The same applies to photodissociation of the dimer of 2-oxopyrimidine (D4). 

Hexahydro-l,3-dimethyl-2-oxopyrimidine, Dimethyl propylene urea, DMPU 42.1 0.352... 

Zigeuner, G., Knopp, C., Blaschke, H. Heterocyclics, 48. Tetrahydro-6-methyl- and -6-phenyl-2-oxopyrimidine-5-carboxylic acids and derivatives. Monatsh. Chem. 1976, 107, 587-603. 

From Krebs et al. (1980). There are typographical errors for the MINDO/3 results in this reference. The minus sign is given instead of the plus for 2-oxopyridine, 2-oxopyrimidine, and 4-oxopyrimidine. 

Cieplak, P., and Geller, M. (1985). J. Mol. Struct. (THEOCHEM) 121, 247—Monte Carlo simulation of water effects on tautomeric equilibrium of 2-oxopyrimidine. 

The enamino nitriles 299, 300, and 302 react smoothly with various isocyanates to afford heterocondensed 4-amino-2-oxopyrimidines (306).172... 

The Karthikeyan P et al. approach (2013) In the Biginelli reaction, a novel l-glycyl-3-methyl imidazolium chloride-coppeifll) complex [[Gmim]Cl-Cu(II)] was synthesized (Scheme 7.21). This was also further studied as oiganocatalyst for enantioselective-substituted 4,6-dimethyl-2-oxopyrimidine-5-caiboxylate derivatives under solvent-free condition at 25 °C [125],... 

Z.T. Wang, S.C. Wang, L.W. Xu, Polymer-supported ionic-liquid-catalyzed synthesis of 1,2,3,4-tetrahydro- 2-oxopyrimidine-5-carboxylates... 

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