Heterocyclic Chemistry – J. A. Joule, K. Mills and G. F. Smith. • Heterocyclic Chemistry (Oxford Primer Series) – T. Gilchrist. • Aromatic Heterocyclic Chemistry . Although heterocyclic compounds may be inorganic, most contain within the ring structure at least one atom of carbon, and one or more elements such as sulfur. The Chemistry of Heterocyclic Compounds, since its inception, has been recognized as a cornerstone of heterocyclic chemistry. Each volume attempts to.

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Heterocyclic Chemistry Fifth Edition John A. Joule School of Chemistry, The University of Manchester, UK Keith Mills Chemistry Consultant, Ware, UK. Each suffix consists of a ring size root and an ending intended to designate the degree of unsaturation in the ring. It is important to recognize that the saturated. KJM - Heterocyclic chemistry. Rings containing one or more heteroatom ( atom other than C). Heteroatoms: N, O, S. Aromatic rings. 5 and 6 membered rings.

Alkyl halides on heating with pyridine give pyridinium salts. Nitration also gives poor yields. The high reactivity of pyridine towards nucleophilic substitution can cause displacement of even powerful hydride H— ion, e. Attack of nucleophile at C-2, C-3 and C-4 gives different resonating structures Scheme 5.


Since the intermediate resulting from nucleophilic attack at C- 2 and C-4 is more stable, nucleophilic substitution at these positions is preferred.

Other nucleophilic substitution reactions of pyridine are given below eqs. If the leaving group at C-2 and C-4 are different, the incoming nucleophile will preferentially substitute for the weaker base the better leaving group eqs. However, in dilute solutions it undergoes protonation of nitrogen to give indolium cation in which the aromaticity of benzene ring is retained eq.

Indole does not undergo easy alkylation of nitrogen unlike amines for the same reason. Therefore, the heterocyclic ring of indole is more reactive towards electrophiles compared to its benzene ring.

The electrophilic substitution in indole takes place at C-3 and not at C-2 as in pyrrole. This can be explained from the following observations. Some typical examples of electrophilic substitution of indole are given below Fig.

If C-3 of indole is blocked, then electrophilic substitution takes place at C-2 and if both C-2 and C-3 are blocked, then electrophilic substitution takes place preferably at C-6 in aromatic ring.

The C2-C3 double bond of indole is labile and can be easily cleaved by ozonolysis, peracids and sodium hypoiodate etc. Indole gives a resinous material whereas 3- substituted or 2,3-disubstituted indoles undergo C2-C3 cleavage as in case of ozonolysis eqs.

The five membered ring is reduced by a number of reagents in acidic media e. Zn, HCl Both are weakly basic and undergo protonation of nitrogen without affecting the aromaticity of the ring.

Quaternary ammonium salts are formed on nitrogen by alkylation. However electrophilic substitution of quinoline and isoquinoline requires less vigorous conditions than pyridine. Electrophilic substitution of protonated quinoline and isoquinoline takes place on the carbocyclic ring at C-5 or C-8 positions.

Some typical examples of electrophilic substitution in quinoline Fig. Quinoline undergoes Chichibabin reaction to give 2- aminoquinoline eq. Isoquinoline undergoes substitution faster than quinoline. The reaction proceeds in a manner analogues to pyridine. NaNH2, liq.

Heterocyclic Chemistry

Quinoline can be converted to 1,2,3,4-tetrahydroquinoline by catalytic hydrogenation or with tin and hydrochloric acid eq. Et2AlH NH However, pyridine-2,3-dicarboxylic acid is not stable and undergoes decarboxylation to give nicotinic acid eq.

Quinoline and isoquinoline both form N-oxides when treated with hydrogen peroxide in acetic acid or with organic peracids. KMnO Organic Chemistry by I. Finar 2. Organic Chemistry by R. Morrison and R. Boyd 3. Acheson 4. Heterocyclic Chemistry by R.

Bansal 26 Related Papers. Three-Membered Rings. Four-Membered Rings. Five-Membered Rings. Cyclizations Involving Two Functional Groups.

Cyclizations of Imines of Amino Acids. Addition of Amino Acids to Unsaturated Compounds. From Unsaturated Amino Acids. From Aminomalonates.

Six-Membered Rings. Seven-Membered Rings. Bicyclic Ring Systems. All rights of reproduction in any form reserved. Systems with One Heteroatom at a Ring Junction. Systems with Two Heteroatoms. Presently several omprazole analogues like lanoprazole, pantoprazole have been introduced [5].

Omeprazole Pantoprazole 2.

[PDF] Heterocyclic chemistry

The large number of highly effective and relatively non-toxic drugs available for the treatment of bacterial infections has provided tough competition for the medicinal chemist, attempting synthesis of new antibacterial agents.

Some triazine derivatives have found to have antibacterial activity[6]. Quinine, Chloroquinine, Primaquinine are known for higher activity to treat malaria and have lower toxicity [7]. Helminthic infections contribute to malnutrition, anemia, stunted growth, cognitive impairment, and increased susceptibility to other diseases. Benzimidazole, pyrazine, isoquinoline, tetrahydropyramidine, tetrahydro quinolone, piperidine, piperazine, triazoles, indoleisoxazole derivatives are the different types of heterocyclic used as anthelmintics.

Albendazole is the most active anthelminitic drug [8].

Also read: ACI 309-72 PDF

Benzimidazole Albendazole 2. Paroxetine, reboxetine, are some of most useful antidepressants containing heterocyclic moiety in their structure. Some piperidine and pyrimidine derivatives also possess antidepressant activity. A variety of small molecule nano-peptide heterocyclics have been discovered and shown to possess antidepressant activity [9].

Paroxetine Reboxetine 2. These agents are used for treatment of cancer or either kill cancer cells or modify their growth. Compounds that alkylated www. Different types of quinozoline and pyrimidine derivatives possess anticancerous activity[10]. Quinozoline Pyrimidine 3. Conclusion The heterocylic compounds are one of the most important and and well known organic compound which is a common and integral feature of a variety of natural products and medicinal agents.

Heterocylic nucleus is present as a core structural component in a range of drug categories such as antimicrobial, anti-inflammatory, antiviral, anticancerous, antihypertensive, antimalarial, antidepressant, antihelmintic activities and many more. References: [1] Katritzky.Arun Prasad.


For the asymmetric synthesis of AAs, several heterocyclic systems have been used as chiral auxiliaries. Systems with Two Heteroatoms.

All rights of reproduction in any form reserved. This is because one of the heteroatoms in the ring can be divalent and so more heteroatoms can be incorporated into the five-membered rings than six-membered rings. Isoquinoline undergoes substitution faster than quinoline.

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Quinolines and Isoquinolines. Since the intermediate resulting from nucleophilic attack at C- 2 and C-4 is more stable, nucleophilic substitution at these positions is preferred.

Therefore pyridine is less basic than amines and anilines.