Aryl azides ortho substituents

In the reaction of nitrile compounds with aryl azides bearing a carboxyl424 or nitrile423 function in the ortho position, fused triazoles are formed by further reaction of the 5-amino group with the ortho substituent on the 1-phenyl ring. Whereas a-cyanomethylene phosphonate gives the expected... 

Undesirable photochemical reactions occur with many aryl azides that have ortho substituents, which should be avoided. Intramolecular reaction of the nitrene results in wastage of the photogenerated intermediates, e.g. Fig. 3.4. 

Although the thermal azepine formation from aryl azides is of rather limited synthetic potential,7,174 the photochemical reaction has some generality. Sundberg et al. obtained 3//-azepines in yields of 33-67% along with the corresponding anilines and other by-products by photolysis of a variety of substituted phenyl azides in diethylamine (Eq. 51). When only one ortho substituent was present, the ring expansion usually occurred in the direction away from this substituent. The transient lH-azepines were detected.236... 

When stripped to its naked minimum, the thermal chemistry of aryl azides is deceptively simple. Excluding those compounds bearing reactive ortho substituents [3] and reactions carried out in the presence of active olefins [4], the thermolysis of an aryl azide simply causes unimolecular loss of nitrogen. The complexity arises in subsequent steps where intervention of the various intermediates shown in Figure 1 has been postulated to precede formation of isolatable products. The photolysis of aryl azides is further complicated by the inclusion of reactions originating from electronically excited singlet and triplet states of the azide itself [5]. In essence, a clear understanding of aryl azide chemistry requires the description of the participation and role of each of these reactive intermediates under various reaction conditions. 

Thermolysis of phenyl azide leads to loss of nitrogen with formation of phenyl nitrene. This conclusion is well supported by experiment. Walker and Waters [6] studied the pyrolysis of phenyl azide at 130°C and confirmed the observations of Smith and Hall [7] from 2-substituted azido biphenyls that thermolysis of aryl azides, lacking ortho-substituents, in inert solvents leads... 

Substituted aryl azides react via the benzazirine formed by closure onto the ortho carbon bearing the hydrogen and not the substituent ... 

Heating aryl azides at reflux in a mixture of hydrazine hydrate and ethanol leads to deazidation. This process appears to be a good method of removing azido groups from aryl systems (particularly in the case of azides bearing ortho substituents) ... 

Second, if the azide substituent is ortho to a ring nitrogen atom the precursor aryl azide will normally be a mixture of the azide and its... 

Changing the identity of the ortho substituent of aryl azides dramatically influences its reactivity toward transition metals. Shen and Driver discovered that substitution of a vinyl group with an iminyl moiety enables Fe(II)-catalyzed benzimidazole (65) formation (Scheme 16.29) [48]. It was proposed that coordination of iron(II) bromide to the imino nitrogen of 64 facilitates the C—N bond formation through nucleophilic attack of an azido nitrogen to the activated imino carbon, leading to B. Expulsion of N2 followed by tautomerization affords the benzimidazoles 65. 

Diphenyl- -triazole is aminated by reaction with hydroxylamine-0-sulfonic acid. The I - and 2-aminotriazoles are formed in approximately equal amounts. Intramolecular amination of 1- and 2-aryltriazoles is achieved by generating a nitrene intermediate in the ortho position of the aryl substituent for example, in the thermolysis (Scheme 42) of the azide (17). ... 

The synthesis of aromatic azides (Scheme 37) from aryl halides with azide ions (SxAr) is particularly successful with systems that carry an activating substituent, an electron-withdrawing group, either in the ortho or the para position relative to the potential leaving group." -" A table with numerous examples can be found in the literature." Fluoride ion as a leaving group is superior to the other halides. Dipolar aprotic solvents, such as DMF for instance, have their special merits in these transformations, too. The reaction of 2,4- or 2,6-dinitroaryl halides with azide ions was shown to be accelerated in micelles or in the presence of quaternary ammonium salts." ... 

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