Pyrimidine continued

Pyrimidine (Continuation) Trifluoro-5-trifluoromethyl- EI0b2, 407 (Educt)... 

Solid-phase syntheses of pyrimidines continue to appear at a rapid pace. Solid-phase syntheses of olomoucine from 4,6-dichloro-2-(methylthio)-5-nitropyrimidine <02TL8071> and of 2,6-disubstituted 4(3//)-quinazolinones from 2,4-dichloro-6-hydroxyquinazoline <02TL2971> have been developed. 2-(Arylamino)quinazolinones 83 were accessed by a traceless parallel solid-phase route from 2-nitrobenzamides 82 <02JOC5831>. A solid-phase synthesis of quinazolin-4(3W)-ones with 3-point diversity relied on the use of immobilized arylguanidines <02TL5579>. 

Solid-phase syntheses of pyrimidines continue to appear at a rapid pace. A solid-phase synthesis of 4-(2-amino-6-phenylpyrimidin-4-yl)benzamide was directly scaled up in excellent yields and high purity <03OPRD553>. The synthesis of imidazo[l,2-a]pyrimidines 59 via condensation of a solid-supported a-bromoketone and 2-aminopyridines was reported <03TL6265>. Pyrimido[4,5-t/]pyrimidine-2,4(l//,3W) diones have been accessed via a versatile solid-phase synthetic route <03S1739>. A microwave-assisted solid support synthesis of 5-methyl-6-ethylcarboxyIate-2-thioxothieno[3,2-iflpyrimidine-4(l//)-ones from 2-amino-3,5-diethyl carboxylate-4-methylthiophene and monosubstituted thioureas was reported <03BKC1038>. 

Diazines. - The pyrimidines continue to attract much attention from every aspect including synthesis of the pyrimidine ring system. The reaction of 8-aminocrotonamide (1 8) with dibasic acid derivatives such as anhydrides or esters gives 2-(substituted)-6-methylpyrimidin-4.-ones (149). However, maleic anhydride reacts to... 

The best way to make pyrimidine in quantity is from 1,1,3,3-tetraethoxypropane (or other such acetal of malondialdehyde) and formamide, by either a continuous (58CB2832) or a batch process (57CB942). Other practical ways to make small amounts in the laboratory are thermal decarboxylation of pyrimidine-4,6-dicarboxylic acid (744), prepared by oxidation of 4,6-dimethylpyrimidine (59JCS525), or hydrogenolysis of 2,4-dichloropyrimidine over palladium-charcoal in the presence of magnesium oxide (53JCS1646). 

Completely trivial names continue in use for good reasons, of which an important one is the need for a simple name for frequent communication concerning a commonly encountered compound or structure. For obscure compounds there is surely neither need nor desirability to perpetuate trivial names, and coining new trivial names is almost never justified. Let us, however, consider purine , the trivial name for what might more systematically be named imidazo[5,4-ring system is so important in biochemistry that exclusive use of one of the systematic names would be intolerable. If the name purine were not available, another short trivial name would inevitably be coined, or even an acronym ( IP or TAP ). It is better to retain the name sanctioned by roughly a century of use, and benefit from a link in comprehension with the past. 

The current work indicates that sulfided platinum catalysts are, in general, more active and selective than Pt, Pd, or sulfided Pd catalysts for reductive alkylation of primary amines with ketones. The choice of the catalyst preparation parameters, especially the support, plays a major role in determining the performance of the catalyst. Diamines, especially of lower molecular weight, tend to react with ketones even at room temperature to form heterocycles such as imidazolidine, diazepanes, and pyrimidines. Hence, a continuous reactor configuration that minimizes the contact between the amine and the ketone, along with a highly active catalyst is desired to obtain the dialkylated product. In general, sulfided Pt appears to be more suited for the reductive alkylation of ethylenediamine while unsulfided Pd or Pt may also be used if 1,3-diaminopropane is the amine. 

The photodimerization of pyrimidine bases continues to attract attention, undoubtedly because of the biological implications of such transformations. 1,3-Dimethyluracil affords four [ 2 + 2] dimers on irradiation in an ice-matrix.192 Analogous dimeric species have been obtained under a variety of conditions from dimethylthymine,193 tetramethyluracil,194 5-methyloro-... 

In DNA, base pairing occurs between guanine and cytosine in its most stable form [87], as in [92]. However, cytosine in its imino form [91] is able to form a hydrogen bond to adenine as in [93], and such a base pairing could lead to the formation of mutations if it continued in DNA replication. The kinetics of the tautomerisation of purine and pyrimidine bases has been... 

The continuing interest in the chemistry of the 1,3-oxazines and the related thiazines and pyrimidines may arise in part from their versatile synthetic applicability and their pharmacological usefulness. Although six-membered saturated or partially saturated 1,3-heterocycles and their derivatives fused with a benzene ring have been thoroughly studied since the beginning of the twentieth century, much less attention has been paid to their saturated counterparts, the related cycloalkane-fused bicyclic 1,3-heterocycles. 

Problem 10-9. Consider two pyrimidine molecules, located in space so that the planes of both molecules are parallel to the y — 2 plane, such that a translahon along the a —axis by 3.4 A and a rotahon by 36° around the a —axis will bring the two into coincidence. (This geometry is an extremely rough model for part of one shand of a DNA double helix). continues... 

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