Heterocyclic aromatic rings

Azadienes undergo Diels-Alder reactions to form pyridine, dihydro- and tetrahydropyridine derivatives. N-Vinyl lactim ethers undergo Diels-Alder reactions with a limited set of dienophiles. " Thioketones react with dienes to give Diels-Alder cycloadducts. The carbonyl group of lactams have also been shown to be a dienophile. Certain heterocyclic aromatic rings (among them furans) can also behave as dienes in the Diels-Alder reaction. Some hetero dienes that give the reaction are -C=C-C=0, 0=C-C=0, and N=C-C=N. ... 

Kaiser et al. reviewed the microbial metabolism of different nitrogen compounds [320], There is agreement among the authors in suggesting an initial step in the transformation of quinoline (by whole cells) that consists of a hydroxylation at position 2 of the heterocyclic aromatic ring, leading to 2-hydroxyquinoline (see Fig. 21 [321]). 

The most widely used herbicides today are triazine compounds (three nitrogens in the heterocyclic aromatic ring). Atrazine is used especially on com but also on pineapple and sugarcane. It is synthesized by reacting cyanuryl chloride successively with one equivalent of ethylamine and one equivalent of isopropylamine. Cyanuryl chloride is made in one step from... 

Purine is one of many fused heterocyclic compounds whose rings share two atoms and the bond between them. For example, the following compounds all contain fused heterocyclic aromatic rings ... 

Gibson, S., McGuire, R. and Rees, D.C. (1996). Principal Components Describing Biological Activities and Molecular Diversity of Heterocyclic Aromatic Ring Fragments. J.Med.Chem., 39, 4065-4072. 

NUCLEOTIDES AND NUCLEIC ACIDS Each nucleotide contains three components a five-carbon sugar (either ribose or deoxyribose), a nitrogenous base, and one or more phosphate groups (Figure 1.12). The bases in nucleotides are heterocyclic aromatic rings with a variety of substituents. There are two classes of base the bicyclic purines and the monocyclic pyrimidines (Figure 1.13). 

The improved electrochemical synthesis (7) of poly pyrrole has led to its use as coating for the protection of n-type semiconductors against photocorrosion in photoelectrochemical cells. (8,9) Recently, it was announced that pyrrole was not the only five-membered heterocyclic aromatic ring compound to undergo simultaneous oxidation and polymerization. Thiophene, furan, indole, and azulene all undergo electrochemical polymerization and oxidation to yield oxidized polymers of varying conductivities (5 x 10 3 to 102 cm- ). (10-13) The purpose... 

---