Aromatic heterocyclic containing

Aromatic heterocycles containing two nitrogen atoms are best reduced by catalytic hydrogenation. Other reduction methods may cleave some of the rings. Even catalytic hydrogenation causes occasional hydrogenolysis. 

Five-membered non-aromatic heterocycles containing one heteroatom Pyrrolidine... 

Five-membered non-aromatic heterocycles containing more than one heteroatom 1-Pyrazolines, 1,3-dioxolanes, 2-pyrazolines Five-membered aromatic heterocycles containing one heteroatom Pyrrole, furan, thiophene... 

Five-membered aromatic heterocycles containing more than one heteroatom... 

Chlorine in 2-chlorolepidine (21) is very reactive, since the compound can be considered an imide chloride. It is readily replaced by hydrogen to form lepidine (22 equation 48). Similarly (23) is converted to (24) on catalytic hydrogenation (equation 49). The above reductions may be applied to many six-membered aromatic heterocycles containing chlorine on the carbon next to nitrogen thus pyridones,... 

Pyrrole is a five-membered aromatic heterocycle containing six n electrons. Five important resonance hybrid structures distribute the 7C-electron pair of the nitrogen atom over the four carbon atoms, and the dipole moment of pyrrole (1.84 daltons similar to water) in the gas phase is directed in a way to make the nitrogen atom the positive end of the dipole. Pyrrole carbon atoms are therefore extraordinarily rich in electrons (Gossauer, 1984). The H-NMR spectrum is of the expected AB type (Figure 6.2.1) the chemical shifts are similar to the ones of benzene. 

SYNTHESIS AND CHEMICAL TRANSFORMATION OF SIX-MEMBERED AROMATIC HETEROCYCLES CONTAINING PERFLUOROALKYL GROUPS... 

Major types of cyclization reactions used for the synthesis of aromatic heterocycles containing fluoroaUcyl group include (but, not limited to) cycloadditions, nucleophilic, and electrophilic cyclizations. 

Selective formation of aromatic heterocycles containing 4-CF3-pyridine unit under action of TiCl4 on RCH=C[C(0)CF3]2 (R = ArNH—) was reported by Soufayne et al., however, in detailed investigation carried out by the Schlosser research group, " it was shown that the cyclization of enamines 51 under action of P (0)Cl3 leads to regioselective formation of 2-CF3-quinolines 52 and 53 (Fig. 7.16). 

PERFLUORINATED SIX-MEMBERED AROMATIC HETEROCYCLES CONTAINING ONE OR MORE HETEROATOM... 

A similar approach was used in case of aromatic fluorinated heterocycles. Ring-fluorinated pyridines containing one, two, and three fluorine substituents are reviewed in Chapter 6, whUe Chapter 7 focuses on the synthesis and typical chemical transformations of aromatic heterocycles containing perfluoroalkyl groups. 

Oxadiazoles (1) are five-membered aromatic heterocycles containing two nitrogen and one oxygen heteroatoms. The majority of 1,2,4-oxadiazoles systems are disubstituted at both the C(3) and C(5) positions (Figure 1). 

Petrov VA (2009) Synthesis and chemical transformation of Six-membered aromatic heterocycles containing perfluoroalkyl groups. In Petrov VA (ed) Fluorinated heterocychc compounds synthesis, chemistry, and applications. Part I. Wiley, Hoboken, pp 273-301... 

Furan 84 is a five-membered r-excessive aromatic heterocycle containing one hetero oxygen atom. It is unstable in acids, forming tars, so like pyrrole (Chapter 6, p 182) the substrate cannot be sulfonated by sulfuric or chlorosulfonic acid. However, again like pyrrole, treatment of furan 84 with sulfur trioxide in either dioxan or pyridine yields the 2-sulfonic acid 85 (Equation 23). 

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