Arene azidation

Nucleophile substitution of the T1 resin synthesis of phenols, biaryls, alkyl arenes, azides, aromatic hydrazines, halides, ester, azo compounds cinnolines, benzotriazoles [129-137, 140, 141]... 

The preparation of amines by the methods described m this section involves the prior synthesis and isolation of some reducible material that has a carbon-nitrogen bond an azide a nitrile a nitro substituted arene or an amide The following section describes a method that combines the two steps of carbon-nitrogen bond formation and reduction into a single operation Like the reduction of amides it offers the possibility of prepar mg primary secondary or tertiary amines by proper choice of starting materials... 

The closely related N- arylazoaziridine system (278) decomposes in refluxing benzene to give aryl azides and alkenes, again stereospecifically (70T3245). However, biaryls, arenes and other products typical of homolytic processes are also formed in a competing reaction, although this pathway can be suppressed by the use of a polar solvent and electron withdrawing aryl substituents. 

The thermolysis of tosyl azide in a variety of arene substrates bearing electron-withdrawing substituents results in poor (1.5-20%) yields of the corresponding 1-tosyl-l//-azepines, e.g. 

Ring expansion of the benzene ring of a calix[6]arene to a 1 //-azepine in 14% yield by photolysis of an aryl azide confined in the calix structure has been reported.294... 

In contrast to the acyl- and sulfonylnitrenes described in this section, arylnitrenes produced thermally or photolytically from aryl azides, including those bearing strongly electron-withdrawing substituents (e.g., CN, N02, CF3), fail to promote ring expansion of arenes to 1H-azepines, although intermolecular substitution of electron-rich substrates, e.g. mesitylene and A.TV-dimethylaniline, have been noted.167... 

A. Dondoni and A. Marra, Addressing the scope of the azide-nitrile cycloaddition in glycoconjugate chemistry. The assembly of C-glycoclusters on a calix[4] arene scaffold through tetrazole spacers, Tetrahedron, 63 (2007) 6339-6345. 

Arylamines and hydrazines react with tosyl azide under basic conditions to yield aryl azides [1] and arenes [2], respectively, by an aza-transfer process (Scheme 5.25). Traditionally, the reaction of anilines with tosyl azides requires strong bases, such as alkyl lithiums, but acceptable yields (>50%) have been obtained under liquidiliquid phase-transfer catalytic conditions. Not surprisingly, the best yields are obtained when the aryl ring is substituted by an electron-withdrawing substituent, and the yields for the corresponding reaction with aliphatic amines are generally poor (-20%). Comparison of the catalytic effect of various quaternary ammonium salts showed that tetra-/i-butylammonium bromide produces the best conversion, but differences between the various catalysts were minimal [ 1 ]. 

TosN, (0.37 g, 2 mmol), the arylhydrazine (2 mmol), and TEA-Br (0.1 g, 0.5 mmol) in xylene (10 ml) are added to aqueous NaOH (50%, 10 ml) and the mixture is refluxed until the azide has been fully consumed (2-10 h). The organic phase is separated and the aqueous phase is extracted with PhH (3 x 10 ml). The combined organic solutions are dried (MgS04) and evaporated to yield the arene [e.g. PhH 40% (6 h) pyridine 98% (6 h) from 2-hydrazino derivative pyridazine 79% (8 h) from 3-hydrazino derivative)]. 

Bei einem neueren Verfahren zur direkten elektrophilen Aminierung von Arenen verwendet man als Reagenz Triazenium-tetrachloroaluminat (Aminodiazonium-tetrachloroalumi-nat), das in situ aus Natrium-azid, Aluminiumchlorid und Chlorwasserstoff in dem zu aminierenden Aren als Solvens erzeugt wird2. 

McEwan and co-worker" examined the acid-catalyzed decomposition of unsymmetrical benzhydryl azides 18 and some related species (Fig. 13.11). The aryl migration step showed very little discrimination between aryl rings with electron-donating and those with electron-withdrawing substituents. This low selectivity was judged to be more consistent with formation of a discrete nitrenium ion intermediate (19). These workers reasoned that a concerted migration would exhibit higher selectivity toward donor-substituted arenes, because in that mechanism the electrons from the arene would participate in the reaction. 

Nitrenium ions have also been generated through the decomposition of azides under acidic conditions (e.g., trifluoroacetic acid-arene solvent mixtures). There are two potential pathways for the formation of the nitrenium ion from the precursors (Fig. 13.24). The first involves initial dissociation of the azide 41 to give a singlet nitrene 42, followed by proton transfer to the latter to yield the primary nitrenium ion 43. The second involves acid-induced decompostion of the azide, whereby preprotonation of the azide (44) forms the primary nitrenium ion in a direct manner. As with the hydroxylamine route, this method is limited to acidic or protic media. 

Takeuchi and co-workers showed that the ratio of N- to C-substitution on the apparent intermediate 75a by a series of aromatics in arene/TFA mixtures was sensitive to the structure of the precursor to 75a (phenyl azide, N-phenylhydroxylamine or O-trifluoroacetyl-N-phenylhydroxylamine) even though the decomposition rates of these precursors were unaffected by the identity of the arene. This result is consistent with the characterization of 75a from N3 and Br trapping studies as a short-lived intermediate that will usually react through ion pair or preassociation processes that may be leaving-group dependent. ... 

Alan H. Haines, Methods for the Oxidation of Organic Compounds, Alcohols, Alcohol Derivatives. Alkyl Halides, Nitroalkanes, Alkyl Azides, Carbonyl Compounds, Hydroxyarenes and Amino-arene s, 1988... 

A stereospecific synthesis of aziridine 266 has been reported by Ittah et al. from arene oxide 1 by treatment with sodium azide, followed by tri-phenylphosphine reaction. The reaction proceeds via a phosphonium hydroxide intermediate (267).157... 

Soft and polarizable nucleophiles, e.g., azide, thiol anions, and phenoxides, add readily to arene oxides, whereas harder anions like carbanions and... 

The reagent system TMS-azide/triflic acid performs efficient animation57 of arenes, while the combination of TMS-azide and A-bromosuccinimide with Nafion-H transforms alkenes into /J-bromoalkyl azides58. On the other hand, the combination of TMS-azide and chromium trioxide converts alkenes into a-azidoketones59 and aldehydes into acyl azides60. 

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