Heterocyclic aromatic compounds groups

A large group of heterocyclic aromatic compounds are related to pyrrole by replacement of one of the ring carbons p to nitrogen by a second heteroatom Com pounds of this type are called azoles... 

Acridine is a heterocyclic aromatic compound obtained from coal tar that is used in the syn thesis of dyes The molecular formula of acndine is C13H9N and its ring system is analogous to that of anthracene except that one CH group has been replaced by N The two most stable reso nance structures of acridine are equivalent to each other and both contain a pyndine like struc tural unit Wnte a structural formula for acridine... 

From the preparative point of view, reactions of heterocyclic aromatic compounds with nucleophilic reagents are very important, especially the reactions of their quaternary salts containing a formal enamine grouping in the molecule. 

Like the piperidones, a wide variety of TV-heterocyclic aromatic compounds show an ability to activate electrophilic functional groups. It is known that acetophenone is completely protonated in CF3SO3H, however in the presence of benzene there is no hydroxyalkylation (condensation) reaction.12 On the other... 

Heterocyclic aromatic compounds a. Pyridine and other azabenzenes. The azabenzenes, compounds in which — N= groups replace —CH= groups, often bear remarkable chemical spectroscopic similarities to the parent homooyclic hydrocarbons. This is associated with their being 7r-isoelectronic with them. 

Structure and Nomenclature. The pyridine group consists of a six-membered, heterocyclic, aromatic compound with one nitrogen atom in the ring. The parent compound of this group is pyridine I with ring positions numbered as shown. Alternative denotations of the I. 2, and 4 positions in the ring are alpha, heta, and gamma, respectively. 

Nucleophilic Reactions of Aromatic Heterocyclic Bases Heterocyclic aromatic compounds containing a formal imine group (pyridine, quinoline, isoquinoline, and acridine) also react readily with nucleophilic reagents. A dihydro-derivative results, which is readily dehydrogenated to a new heteroaromatic system. Since the nucleophile always attacks the a-carbon atom, the reaction formally constitutes an addition to the C=N double bond. An actual localization of the C=N double bond in aromatic heterocyclic compounds is incompatible with molecular orbital theory. The attack of the nucleophilic reagent occurs at a site of low 77-electron density, which is not... 

The reaction has been shown to be of very broad scope with a multitude of nucleophiles Nu such as imides.23,24,29,32,33,36,37,42 amines,10,32 cyanide,25,32 hydroxide,10,32 alkox-ide,10,26,32 electron-rich isocyclic or heterocyclic aromatic compounds,28 carboxamides,31 lactams,31 ureas,31 sulfonamides,31 cyanate,31 formate (to give products with Nu = H),34 C-H acidic compounds,35 hydrazines and hydrazides,38 and sulfinates.38 The amino group NR R2 of cyclopropane-1,1-diamines and the nucleophile Nu in bicycles 8, 9 or 12, respectively, can be easily replaced with other nucleophiles Nu, such as water,10,32,33 alkoxide,10,32-34,42 Grignard compounds,27,42 amines,29,30,36,37,42,43 cyanide,29,33,42,44 hydride,34,42,44 and C-H acidic compounds39-41,43,44 (see Section 5.2.1.). Therefore, it is currently the most important method for the preparation of substituted bicyclic cyclopropylamines. The toxic and costly reagent methyl fluorosulfate can be avoided in a modified synthetic route, which instead of the fluorosulfate 5 proceeds via the corresponding tetraphenylborate, hexafluorophosphate, or (most conveniently) via the tosylate.23 The different steps of the method can often be combined in a one-pot procedure. Results are summarized in Table 3. 

Compounds in the two groups differ in a number of ways. The two differ chemically in that the aliphatic undergo free-radical substitution reactions and the aromatic undergo ionic substitution reactions. In this chapter you examine the basics of both aromatic and heterocyclic aromatic compounds, concentrating on benzene and related compounds. 

Six-Membered Heterocyclic Aromatic Compounds When a CH group in an aromatic hydrocarbon is replaced by =N, there is very little change in the spectrum, except for a slight intensification of the... 

A plethora of electron-deficient arenes can enter the VNS reaction carbocyclic and heterocyclic aromatic compounds activated by the nitro group and arenes that are active electrophiles due to their electronic configuration, such as azulene [35, 36], electron-deficient annulenes [37], tropylium cation [38], and particularly azines and azinium cations. Interestingly, q -transition metal complexes of arenes, such as benzene tricarbonylchromium, do not enter the VNS reactions. Although the addition of carbanions to these electron-deficient rings proceeds efficiently, and these adducts can be oxidized to form the products of ONSH, the p-elimination of HCl from the o adducts of a-halocarbanions does not occur [39, 40]. 

---