1.2.3- Triazoles tetrazoles

Methods for the synthesis of these systems include the following cyclocondensation (1,2,3- ind 1,2,4-thiadiazoles, benzotriazoles, 1,2,4-triazoles), cycloaddition (1,2,3-triazoles, tetrazoles), cyclodehydration (1,2,5-oxadiazoles) and cyclization (l,2,5-oxadiazole-2-oxides, 1,2,4-thiadiazoles, 1,2,3-triazoles, tetrazoles). 

Similar to 1,2,3-triazoles, tetrazoles can also be synthesized by [3-(-2] cycloadditions [88]. 

Despite the weak basicity of isoxazoles, complexes of the parent methyl and phenyl derivatives with numerous metal ions such as copper, zinc, cobalt, etc. have been described (79AHC(25) 147). Many transition metal cations form complexes with Imidazoles the coordination number is four to six (70AHC(12)103). The chemistry of pyrazole complexes has been especially well studied and coordination compounds are known with thlazoles and 1,2,4-triazoles. Tetrazole anions also form good ligands for heavy metals (77AHC(21)323). 

All triazoles, tetrazoles, and unsymmetrically substituted imidazoles and pyrazoles can exist in two tautomeric forms, e.g., 1 2 and 3 4. However, attempts to isolate the individual tautomers have been unsuccessful, always leading to one isomer (for summaries of this aspect of the tautomerism of imidazoles, see references 1 and 2). Although the isolation of both tautomers of a number of com-... 

The diazotization of heteroaromatic amines is basically analogous to that of aromatic amines. Among the five-membered systems the amino-azoles (pyrroles, diazoles, triazoles, tetrazoles, oxazoles, isooxazoles, thia-, selena-, and dithiazoles) have all been diazotized. In general, diazotization in dilute mineral acid is possible, but diazotization in concentrated sulfuric acid (nitrosylsulfuric acid, see Sec. 2.2) or in organic solvents using an ester of nitrous acid (ethyl or isopentyl nitrite) is often preferable. Amino derivatives of aromatic heterocycles without ring nitrogen (furan and thiophene) can also be diazotized. 

The compounds referred to as azolides are heterocyclic amides in which the amide nitrogen is part of an azole ring, such as imidazole, pyrazole, triazole, tetrazole, benzimidazole, benzotriazole, and their substituted derivatives. In contrast to normal amides, most of which show particularly low reactivities in such nucleophilic reactions as hydrolysis, alcoholysis, aminolysis, etc., the azolides are characterized by high reactivities in reactions with nucleophiles within the carbonyl group placing these compounds at about the same reactivity level as the corresponding acid chlorides or anhydrides. 11... 

Major advancements in the chemistry of pyrazoles, imidazoles, triazoles, tetrazoles, and related fused heterocyclic derivatives continued in 2000. Solid-phase combinatorial chemistry of pyrazoles and benzimidazoles has been particularly active. Synthetic routes to all areas continue to be pursued vigorously with improvements and applications. Notably, metal-promoted and cross-coupling reactions of all classes seemed to be a dominant theme in 2000. Applications of pyrazole-, imidazole-, and 1,2,3-benzotriazole-containing reagents to a wide array of synthetic applications remained active. 

This section is divided into eight subsections, covering imidazoles, pyrazoles, isoxazoles, oxazoles, triazoles, tetrazoles, pyridines, and pyrimidines, purines, and nucleic acid bases respectively. 

A wide range of polymers based on other heterocyclic 5-membered rings have been investigated, including oxadiazole, pyrazole, triazole, tetrazole, and thiophene [Bass et al., 1987 Briffaud et al., 2001 Cassidy, 1980 Critchley et al., 1983 Gebben et al., 1988 Ueda and Sugita, 1988],... 

Table 15.20. Preparation of triazoles, tetrazoles, oxadiazoles, and thiadiazoles.

CATENATED NITROGEN LIGANDS PART II.1 TRANSITION METAL DERIVATIVES OF TRIAZOLES, TETRAZOLES, PENTAZOLES, AND HEXAZINE... 

Catenated nitrogen ligands. Part II. Transition metal derivatives of triazoles, tetrazoles, pentazoles and hexazine. Adv. Inorg. Chem. Radioehem. 32, 171 (1988). 

N-Oxide Azaheterocycle Azole Pyrazole Imidazole Triazole Tetrazole N-Oxidation Cyclization Functionalization Activation Regioselectivity One pot... 

Catenated Nitrogen Ligands Part II. Transition Metal Derivatives of Triazoles, Tetrazoles, Pentazoles, and Hexazine... 

The reaction can be also applied to azoles (e.g., imidazoles, pyrazoles, triazoles, tetrazole) as the N -nucleophile for the hydroaminations of cyclic olefins. In this case, the presence of methyl benzoate sensitizes the photoisomerization of the double bond to form a highly strained ( )-cycloalkene. Protonation of this intermediate by triflic acid (TfOH, 20mol%) and addition of the azole nucleophile completes the reaction sequence [41]. As an example, the expeditious synthesis of l-(l-methylcy-clohexyl)- H-imidazole (27) in 72% yield is shown in Scheme 3.17 [41]. 

An impressive range of nucleophiles was successful for arylboronic acids in the presence of Cu(OAc)2 and base, which included amine, anilines, amides, imines, ureas, carbamates, sulfonamides, and aromatic heterocycles (e.g., imidazoles, pyrazoles, triazoles, tetrazoles, benzimidazoles, and indazoles) (Equation (226)) 996 997 1000-1011 For all the reactions investigated with A-nucleophiles, the use of Et3N resulted in yields superior to those obtained with pyridine, but pyridine was the base of choice for the preparation of imidazole derivatives from heteroarenes. For the tetrazole, NMO and DBU were studied as alternative bases. There are mechanistic studies.999,1002-1013... 

The EC oxidation first wave is diffusive and corresponds to one-electron transfer. An increase in the number of ring nitrogen atoms (the number of nitro group being the same) in a series of imidazole, pyrazole, triazole, tetrazole, as well as an increase in the number of nitro groups in the series nitroazole, di-, and trinitroazole essentially complicates the ability of nitroazole anions to electrochemical oxidation. [920]. In case of bicyclic C-C bound nitroazole dianions there is a dramatic decrease in E1/2 that... 

A large body of information on the methods of synthesis, application, structure, and properties of all known five-membered nitroazoles - pyrazoles, imidazoles, triazoles, tetrazoles, oxazoles, isoxazoles, oxadiazoles, thiazoles, isothiazoles, thiadiazoles, selenazoles, selenadiazoles, and their benzo analogs - indazoles, benzimidazoles, benzoxazoles, benzisoxazoles, benzoxadiazoles, benzothiazoles, benzoisothiazoles, benzothiadiazoles, benzotriazoles, benzoselenazoles, and ben-zoselenadiazoles has been systematized, summarized, and critically discussed in this monograph. 

Early observations on the tautomerism of substituted imidazole and pyrazole derivatives were proved to be general, and to apply also to triazoles, tetrazoles and to related heterocyclic systems such as benzo derivatives. In the formulas of Figure 13 the and atoms may be replaced by other heteroatoms (e.g., N, P) or by CR /CR groups. 

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