ImageFile=Pyrimidine chemical structure.png
Section1= Chembox Identifiers
Section2= Chembox Properties
Section3= Chembox Hazards
Pyrimidine is a
heterocyclic aromatic organic compoundsimilar to benzeneand pyridine, containing two nitrogen atomsat positions 1 and 3 of the six-member ring. [Heterocyclic Chemistry (3rd Edition) Thomas. L. Gilchrist ISBN 0-582-27843-0 ] It is isomeric with two other forms of diazine.
nucleobases found in nucleic acids ( cytosine, thymine, and uracil) are pyrimidine derivatives:
DNAand RNA, these bases form hydrogen bonds with their complementary purines. Thus the purines adenine(A) and guanine(G) pair up with the pyrimidines thymine (T) and cytosine (C), respectively.
RNA, the complement of A is U instead of T and the pairs that form are adenine: uraciland guanine: cytosine.
These hydrogen bonding modes are for classical
Watson-Crick base pairing. Other hydrogen bonding modes ("wobble pairings") are available in both DNAand RNA, although the additional 2'-hydroxyl group of RNAexpands the configurations through which RNA can form hydrogen bonds.Fact|date=February 2007
A pyrimidine has many properties in common with
pyridine, as the number of nitrogen atoms in the ring increases the ring pi electrons become less energetic and electrophilic aromatic substitutiongets more difficult while nucleophilic aromatic substitutiongets easier. An example of the last reaction type is the displacement of the aminogroup in 2-aminopyrimidine by chlorine [ Organic Syntheses, Coll. Vol. 4, p.182 (1963); Vol. 35, p.34 (1955) [http://www.orgsynth.org/orgsyn/pdfs/CV4P0182.pdf Link] ] and its reverse. [ Organic Syntheses, Coll. Vol. 4, p.336 (1963); Vol. 35, p.58 (1955) [http://www.orgsynth.org/orgsyn/pdfs/CV4P0336.pdf Link] ] Reduction in resonance stabilizationof pyrimidines may lead to addition and ring cleavage reactions rather than substitutions. One such manifestation is observed in the Dimroth rearrangement.
Compared to pyridine,
N-alkylationand N-oxidationis more difficult, and pyrimidines are also less basic: The pKavalue for protonated pyrimidine is 1.23 compared to 5.30 for pyridine.
Pyrimidines can also be prepared in the laboratory by
organic synthesis. One method is the classic Biginelli reaction. Many other methods rely on condensationof carbonyls with amines for instance the synthesis of 2-Thio-6-methyluracil from thioureaand ethyl acetoacetate[ Organic Syntheses, Coll. Vol. 4, p.638 (1963); Vol. 35, p.80 (1955) [http://www.orgsynth.org/orgsyn/pdfs/CV4P0638.pdf Link] ] or the synthesis of 4-methylpyrimidine with 4,4-dimethoxy-2-butanone and formamide[ Organic Syntheses, Coll. Vol. 5, p.794 (1973); Vol. 43, p.77 (1963) [http://www.orgsynth.org/orgsyn/pdfs/CV5P0794.pdf Link] ] .
A novel method is by reaction of certain
amides with carbonitriles under electrophilic activation of the amide with 2-chloro-pyridine and trifluoromethanesulfonic anhydride["Single-Step Synthesis of Pyrimidine Derivatives" Mohammad Movassaghi and Matthew D. Hill J. Am. Chem. Soc.; 2006; 128(44) pp 14254 - 14255; (Communication) DOI|10.1021/ja066405m] :
Pyrazine, an analog with the nitrogen atoms in positions 1 and 4
Pyridazine, an analog with the nitrogen atoms in positions 1 and 2
Simple aromatic rings
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