Pyrimidin-4-ones, methylation

Pyrimidin-2-ones, methylation of, 254 Pyrimidin-4-ones, methylation of, 254, 255... 

The following very important observations must be accounted for in any mechanistic proposal cells were incubated with a mixture of (2 -l3C)AIRs and (3-,5N)AIRs. A mass-spectrometric analysis of the product of biosynthesis showed that this was a mixture of two pyrimidines, one labeled at the methyl carbon atom, the other at N-l no pyrimidine twice labeled or unlabeled was observed these latter would have arisen from recombination of fragments carrying C-2 or N-3. The conclusion is that the fragments containing C-2 and N-3, orig-... 

Both DNA and RNA contain the same purine bases adenine (A) and guanine (G). Both DNA and RNA contain the pyrimidine cytosine (C), but they differ in their second pyrimidine base DNA contains thymine (T), whereas RNA contains uracil (U). T and U differ by only one methyl group, which is present on T but absent on U (Figure 22.1). [Note Unusual bases are occasionally found in some species... 

Ac = Acetyl acac = Acetylacetonate bda = Benzylidene-acetone BINOL = l,l -bi-2-naphthol Bn = Benzyl brsm = Yield based on recovered starting material Bu = Bntyl CAN = Ceric anunonium nitrate CBS = Corey/Bakshi/Shibata catalyst [(+) or (—)-(S)-2-methyl-oxazaborolidine] COD = Cyclo-l,5-octadiene COT = Cyclooctatetraene Cp = Cyclopentadienyl Cp = Penta-methylcyclopentadienyl Cy = Cyclohexyl DCC = Dicy-clohexylcarbodiimde DMF = Ai,A-dimethylformainide DMPU = l,3-dunethyl-3,4,5,6-tetrahydro-2(lH)-pyrimidin-one DMSO = Dimethylsnlfoxide dppe = Diphenylphosp-hinoethane dr = Diastereomer ratio dppm = Diphenylphos-phinomethane E = Electrophile ee = Enantiomeric excess EHMO = Extended htickel molecular orbital Et =... 

In pyrimidines, a 4-alkyl- is deprotonated more readily than a 2-aUcyl-gronp here again one sees the greater stability associated with a y-qninonoid resonating anion. Side-chain radical halogenation selects a pyrimidine-5-methyl over a pyrimidine-4-methyl the reverse selectivity can be achieved by halogenation in acid solntion - presnmably an iV-protonated, side-chain-deprotonated species, i.e. the enamine tantomer, is involved. ... 

Many years ago, one of the authors (AJB) had the pleasure of conducting his first arylation reaction - which was a Heck-Mizoroki reaction between an activated pyrimidine and methyl acrylate - and he was struck by the simplicity and efficacy of the coupling process. Thus, a keen interest in these reactions was awakened, and this has been manifested in the recent research activities conducted in this group. 

Preliminary IR spectral studies were said to suggest that pyrimidinones existed as pyrimidinols <50JCS3062) but this conclusion was promptly reversed <52JCS168) on better experimental evidence subsequent comparison with their N- and O-methyl derivatives showed that the pyrimidinones (39a R = H) and (40a R = H) along with their A-methyl derivatives (39a R = Me), (40a R = Me) and (40b R = Me) all exhibited vqo in the range 1600-1700 cm, whereas the methoxypyrimidines (39b R = Me) and (40c R = Me) showed no such absorptions <53JCS33l, 55JCS211). Closer analysis of the spectra for pyrimidin-4-one (40a R= H) showed that the ort/jo-quinonoid form (40a R = H) is the predominant tautomer (see Section 2.13.1.4). 

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