Tetrazoles organic substituent

Many tetrazoles with an organic substituent have been published in open literature. Some of them have the characteristics of piimaiy explosives especially those containing azido, picryl, or other nitrogen-rich functional groups. Unfortunately, many of these substances are too sensitive for practical application. We have therefore decided to limit our selection to only those substances that are referred to as potentially useful primary explosives. 

Unsubstituted tetrazole behaves as an organic acid with acidity close to that of acetic acid. In general, depending on the substituent in position 5, tetrazole ionization occurs in the range from —0.8 unit of the Hq scale to 7 unit of the pH scale. Proton elimination from 1H- and 277-tetrazoles 24 and 106 results in formation of the tetrazolate anion (tetrazolide) 7 (Scheme 5) characterized by high aromaticity and good Jt-electron delocalization. 

These processes were extended to preparation procedures and application to the organic synthesis of organome-tallic tetrazole derivatives, including 5-metallated tetrazoles and tetrazoles with a metal-carbon bond in a substituent, and also of organotin tetrazoles <2005RJ01565>. 

Most transformations of other azoles into tetrazoles involve azido substituents for example, 5-azido-l,2,3-triazoles 753 with a C02Me group at C(4) rearrange at 5070 C in organic solvents into the 5-diazoester substituted tetrazoles 754 (Scheme 325) <1998J(P2)785>. For a comprehensive review on the preparation of tetrazoles from transformations of other heterocycles see <1998JPR687>. 

Carbodiimides are a unique class of reactive organic compounds having the heterocumu-lene structure R—N=C=N—R. They can be formally considered to be the diimides of carbon dioxide or the anhydrides of 1,3-substituted ureas, and they are closely related to the monoimides of carbon dioxide, the isocyanates. The substituent R can be alkyl, aryl, acyl, aroyl, imidoyl or sulfonyl, but nitrogen, silicon, phosphorous and metal substituted carbodiimides are also known. The unsubstituted carbodiimide HN=C=NH is isomeric with cyanamide, H2NCN. Mono substituted carbodiimides, generated in the thermolysis of 1-substituted tetrazoles, can be isolated at liquid nitrogen temperature but isomerize to the cyanamides at higher temperatures. ... 

The Finnegan tetrazole synthesis is the reaction of a functionalized nitrile 1 with hydrazoic acid or an alkyl, aryl, or inorganic azide 2 to generate tetrazole 3 and/or 4. Typically, the 1,5-disubstituted tetrazole or l//-5-substituted tetrazole 3 is the predominant or exclusive product. The reaction can be promoted thermally or by use of mild organic, inorganic, or Lewis acids. The substituents allowed on both the nitrile and azide span a wide variety of functionality however, electron poor nitriles react more smoothly than electron-rich nitriles using standard protocol. 

The first examples of a direct 1,5-substituents tetrazole synthesis via an intermolecular [2 + 3]-cycloaddition reaction of organic azides (based on the results for a similar synthesis of triazoles) were developed by Sharpless et al. in 2002 using sulfonyl or acyl cyaiudes (Scheme 9.8). In both cases, the Click reaction involved simple heating of the organic azides (hindered, aliphatic or aryl azides) and the nitriles into a homogenous liquid at higher reaction temperature (80-100 °C), in which no further purification was necessary. 

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