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Related Concept Videos

Aryldiazonium Salts to Azo Dyes: Diazo Coupling01:11

Aryldiazonium Salts to Azo Dyes: Diazo Coupling

The reaction of weakly electrophilic aryldiazonium (also called arenediazonium) salts with highly activated aromatic compounds leads to the formation of products with an —N=N— link, called an azo linkage. This reaction, presented in Figure 1, is known as diazo coupling and occurs without the loss of the nitrogen atoms of the aryldiazonium salt. Highly activated aromatic compounds such as phenols or arylamines favor the diazo coupling reaction. The coupling generally occurs at the para position.
Nomenclature of Aryl and Heterocyclic Amines01:10

Nomenclature of Aryl and Heterocyclic Amines

The simplest aromatic amine is phenylamine, which contains an –NH2 functionality directly attached to an aromatic ring. The name aniline is designated for this skeleton. As shown in Figure 1, the common names of the functionalized anilines involve prefixes ortho-, meta-, and para- to indicate the substitution position. Different functionalized aniline derivatives also have notable trivial names.
Nucleophilic Aromatic Substitution of Aryldiazonium Salts: Aromatic SN101:14

Nucleophilic Aromatic Substitution of Aryldiazonium Salts: Aromatic SN1

Treating arylamines with nitrous acid gives aryldiazonium salts that are effective substrates in nucleophilic aromatic substitution reactions. The diazonio group in these salts can be easily displaced by different nucleophiles, yielding a wide variety of substituted benzenes. The leaving group departs as nitrogen gas, and this easy elimination is the driving force for the substitution reaction.
In the Sandmeyer reaction, for example, the diazonio group is replaced by a chloro, bromo, or cyano...
Diazonium Group Substitution with Halogens and Cyanide: Sandmeyer and Schiemann Reactions01:20

Diazonium Group Substitution with Halogens and Cyanide: Sandmeyer and Schiemann Reactions

Arenediazonium substitution reactions occur when the diazonium group is substituted by various functional groups such as halides, hydroxyl, nitrile, etc. For instance, arenediazonium salts react with copper(I) salts of chloride, bromide, or cyanide to form corresponding aryl chlorides, bromides, and nitriles. These reactions are named Sandmeyer reactions. Although the mechanism of this reaction is complicated, as illustrated in Figure 1, they are believed to progress via an aryl copper...
Preparation of 1° Amines: Azide Synthesis01:22

Preparation of 1° Amines: Azide Synthesis

Direct alkylation of ammonia produces polyalkylated amines, along with a quaternary ammonium salt. To exclusively prepare primary amines, the azide synthesis method can be used.
Azide ions act as good nucleophiles and react with unhindered alkyl halides to form alkyl azides. Alkyl azides do not participate in further nucleophilic substitution reactions, thereby eliminating the chances of polyalkylated products. Alkyl azides are reduced by hydride-based reducing agents, like lithium aluminum...
Diazonium Group Substitution: –OH and –H01:19

Diazonium Group Substitution: –OH and –H

Nitrous acid, a weak acid, is prepared in situ via the reaction of sodium nitrite with a strong acid under cold conditions. This nitrous acid prepared in situ reacts with primary arylamines to form arenediazonium salts. Such reactions are known as diazotization reactions. As shown in Figure 1, the formation of arenediazonium salts begins with the decomposition of nitrous acid in an acidic solution to give nitrosonium ions.

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Related Experiment Video

Updated: Jun 19, 2026

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
11:45

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles

Published on: August 22, 2018

Access to N2-Substituted (Aza)Indazoles.

Flora Fan1,2, Xiangfeng Niu3, Wanqi Su1

  • 1Discovery Process Chemistry, Small Molecule Process Research & Development, Merck & Co., Inc., South San Francisco, California 94080, United States.

Organic Letters
|June 18, 2026
PubMed
Summary

Medicinal chemists developed a new one-pot synthesis for N2-substituted (aza)indazoles, crucial in drug discovery. This efficient method uses readily available starting materials and a key oxidative cyclization for broad applicability.

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Preparation of Contiguous Bisaziridines for Regioselective Ring-Opening Reactions
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Preparation of Contiguous Bisaziridines for Regioselective Ring-Opening Reactions

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Preparation of Enantiopure Non-Activated Aziridines and Synthesis of Biemamide B, D, and epiallo-Isomuscarine
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Preparation of Enantiopure Non-Activated Aziridines and Synthesis of Biemamide B, D, and epiallo-Isomuscarine

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Preparation of Contiguous Bisaziridines for Regioselective Ring-Opening Reactions
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Preparation of Contiguous Bisaziridines for Regioselective Ring-Opening Reactions

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Preparation of Enantiopure Non-Activated Aziridines and Synthesis of Biemamide B, D, and epiallo-Isomuscarine
11:04

Preparation of Enantiopure Non-Activated Aziridines and Synthesis of Biemamide B, D, and epiallo-Isomuscarine

Published on: June 13, 2022

Area of Science:

  • Organic Chemistry
  • Medicinal Chemistry
  • Heterocyclic Chemistry

Background:

  • N2-substituted (aza)indazoles are prevalent scaffolds in bioactive molecules and drug candidates.
  • Accessing diverse N2-functionalized (aza)indazoles often requires complex synthetic routes.
  • Medicinal chemistry programs require efficient and scalable methods for synthesizing novel heterocyclic compounds.

Purpose of the Study:

  • To develop a practical and efficient one-pot synthetic method for N2-substituted (aza)indazoles.
  • To enable rapid access to a wide range of N2-functionalized (aza)indazoles for drug discovery efforts.
  • To establish a scalable and chromatography-free synthesis protocol.

Main Methods:

  • A one-pot reaction involving amino (aza)benzaldehydes and various amines.
  • Oxidative N-N bond cyclization mediated by phenyliodine(III) diacetate (PhI(OAc)2).
  • Scale-up of the reaction for multigram synthesis without chromatography.

Main Results:

  • Successful synthesis of diverse N2-substituted (aza)indazoles.
  • Demonstration of a key oxidative N-N bond cyclization step.
  • Achieved multigram, chromatography-free synthesis, indicating scalability.

Conclusions:

  • The developed one-pot method provides a practical and rapid route to N2-substituted (aza)indazoles.
  • This protocol is valuable for medicinal chemistry efforts, facilitating the synthesis of drug-like molecules.
  • The scalability and chromatography-free nature of the synthesis enhance its utility for producing compounds in larger quantities.