4- Nitrophenyl azide, reaction with

The most reliable method of preparing benzofuroxans is by decomposition of o-nitrophenyl azides. Decomposition can be achieved by irradiation, or more usually by pyrolysis temperatures between 100° and 1.50° are commonly used. Refluxing in glacial acetic acid is the recommended procedure for 4- or 5-sub-stituted 2-nitrophenyl azides, but with 3- or 6-substituted compounds higher boiling solvents are usually necessary. Quantitative studies on the reaction rate have been made, and a cyclic transition state invoked, an argument which has been used to account for the greater difficulty of decomposition of the 6-substituted 2-nitrophenyl azides. Substituent effects on the reaction rate have also been correlated with Hammett a constants, ... 

In the reaction of p-nitrophenyl azide 123 with ethoxyethylene, the azide is LUMO and dipolarophile is HOMO. Hence, their dominant interaction gives 124 as only product [109]. 

Perhaps one of the most exciting developments in the chemistry of quinoxalines and phenazines in recent years originates from the American University of Beirut in Lebanon, where Haddadin and Issidorides first made the observation that benzofuroxans undergo reaction with a variety of alkenic substrates to produce quinoxaline di-AT-oxides in a one-pot reaction which has subsequently become known as the Beirut reaction . Many new reactions tend to fall by the wayside by virtue of the fact that they are experimentally complex or require starting materials which are inaccessible however, in this instance the experimental conditions are straightforward and the starting benzofuroxans are conveniently prepared by hypochlorite oxidation of the corresponding o-nitroanilines or by pyrolysis of o-nitrophenyl azides. 

Benzofuroxan 79 can be generated from 2-nitrophenyl azide 80 (Scheme 49). Neighboring-group assistance within the pyrolysis leads to a one-step mechanism with an activation barrier of 24.6 kcal/mol at the CCSD(T)/6-31 lG(2d,p) level [99JPC(A)9086]. This value closely resembles the experimental one of 25.5 kcal/mol. Based on the ab initio results for this reaction, rate constants were computed using variational transition state theory. 

Esters of 1,2,3-triazolecarboxylic acids are the most common derivatives of triazole (Section 5.01.9) therefore, their conversions to other, more useful, functionalities are of great importance. In an example given in Scheme 48, 4-triazolecarbocylic ester 317, obtained from a reaction of (3-ketoester 316 with 4-chloro-2-nitrophenyl azide, is hydrolyzed to free acid 318 (82% yield) by 4% KOH. Heated to reflux in DMF for 3 h, acid 318 undergoes decarboxylation to triazole derivative 319 with 81% isolated yield <2004FA397>. 

Phenyl azide reacts slowly with bis(trimethylsilyl)butadiyne at elevated temperature to give 1,2,3-triazole (718) as the only product. Similar reaction of 4-nitrophenyl azide and bis(trimethyl-... 

The triazole ring can be synthesized by reaction between a suitable pyridine (or piperideine) and an azide. Thus 5-nitro-2-pyridone (or N-substituted pyridones) and sodium azide give a 5-oxotriazolo[4,5-b]pyridine (94)182-184 whereas the enamine 95 reacts with p-nitrophenyl azide to give the hexahydro-l//-triazolo[4,5-c]pyridine 96.185,186... 

The addition reactions of aryl azides onto enamines bearing a carbonyl, sulfonyl, or nitro group in the 0 position with respect to the nitrogen atom have been investigated by Italian authors.240-241 The expected triazoline derivatives could not be isolated but were immediately converted into the corresponding 1,2,3-triazoles (49) and secondary amines. The reaction of p-nitrophenyl azide with l-benzoyl-2-morpholino-l-propene (48) is given as a typical example. 

As well as the previous chapter on the Hammett equation,1 the importance of the approach has found expression in specific areas in other contributions to these volumes side chain reactivities of thiophenes 17 tautomerism 18 reactions of azines with nucleophiles 19,20 formation of benzofuroxans by decomposition of o-nitrophenyl azides 21 acid dis-... 

A study of ketene A, O-acetals has shown that such compounds derived from lactam acetals may be used in the preparation of larger heterocyclic systems via reaction with a 1,3-dipolar species, the initial cycloadducts stabilizing their structures by aromatization. Pyrrolo[2,3-i/]-l,2,3-triazole derivatives, however, do not undergo such elimination reactions and stable cycloadducts may be obtained. Thus, the lactam acetals (133) give the ketene A,0-acetals (134), which on reaction with p-nitrophenyl azide yield substituted pyrrolo[2,3-d]-l,2,3-triazole derivatives (135) <86CB359l>. 

The generation and reactions of arylnitrenes continue to attract attention. Evidence for a photoinitiated autocatalytic chain mechanism in the photodecomposition of phenyl azide has been reported, and the reaction of photochemically generated phenyl nitrene with oxygen has been reexamined. Irradiation of p-azidoaniline in aqueous solution yields triplet p-aminophenyl nitrene, which on reaction with water is converted into the highly reactive p-benzoquinone diimine. Both m- and p-nitrophenyl azides, on photoelimination of nitrogen at 77 K, afford the corresponding nitrenes, whereas o-nitrophenyl azide (93) is converted without the intermediacy of a nitrene into the benzofurazan (94). 4,4 -... 

The thermal decomposition of sulfonyl azides, like azido formates, appears to involve nitrene intermediates . The thermolysis of benzenesulfonyl azide is first order and the rate coefficient is relatively insensitive to solvent changes or substituent effects . o-Nitrobenzenesulfonyl azide decomposes with evolution of nitric oxide and nitrogen the rate of azide disappearance however, is about the same as that for other benzenesulfonyl azides and it appears that the reaction leading to NO can be explained by an intramolecular rearrangement in the nitrene intermediate. This is in contrast to the decomposition of o-nitrophenyl azide (vide infra) where rearrangement occurs in the transition state of the rate-determining step. 

Benati, L., Calestani, G., Nanni, D., Spagnolo, P. Reactions of Benzocyclic 3-Keto Esters with Tosyl and 4-Nitrophenyl Azide. Structural Influence of Dicarbonyl Substrate and Azide Reagent on Distribution of Diazo, Azide and Ring-Contraction Products. J. Org. Chem. 1998, 63, 4679-4684. 

A number of cyclopropyl-substituted five-membered heterocycles have been synthesized by addition of various 1,3-dipolar reagents to (alk-l-enyl)cyclopropanes. Most reactions were performed using tricyclo[3.1.0.0 ]hex-3-ene and tricyclo[3.1.0.0 ]hex-3-en-3-yl phenyl sul-fone, giving the corresponding cycloadducts in very good yields on treatment with azides, a carbonyldicobalt complex, nitrile oxides, diphenylni-trilimine, (4-nitrophenyl)benzenecarbonitrile ylide, and diazoalkanes. For example, addition of tricyclo[3.1.0.0 ]hex-3-ene (1) to 4-nitrophenyl azide gave dihydro-1,2,3-triazole 2 in 94 /o yield. ... 

The first report of the preparation of quinoxaline di-N-oxides from benzofuroxans was by reaction with enamines. Benzofuroxans are themselves conveniently prepared by oxidation of the appropriate o-nitroanilines with hypochlorite or by pyrolysis of the corresponding nitrophenyl azides. A variety of enamines react satisfactorily, but the less reactive morpholine enamines give higher yields and more easily isolata-ble products (Scheme 5). " ... 

Cyclic ketones are converted smoothly to diazo ketones in the presence of HMPA. 4-Nitrophenyl azide (128) exhibits a diazo transfer reaction with malonates and cyclic 1,3-cyclohexanedione (128) in some cases diazo compound 129 further leads to fused triazole derivative (130) formation.52... 

The ring expansion of phenyl azides on irradiation and the concomitant ring expansion to a didehydroazepine and subsequent trapping provides a useful synthetic route to a variety of azepine systems. Thus irradiation of695, with a variety of/7-substituents, occurs readily in THF/water to yield the azepinones 696. Interest in the influence of other substituents on this process has been recorded in the study of the reactions of 3- and 4-nitrophenyl azides" ". This work has illustrated the profound effect that substituents can have on the reaction. Ring expansion is also observed for a tyrosine derivative". Irradiation of 697 in excess diethylamine brings above the exclusive conversion into 698 76. 

Evans et al. [50] examined the DBU (l)-mediated azidation of a-hydroxy ester with phosphoryl azides and found that the amount of DBU (1) is critical for asymmetric induction (Table 3.3). In the reaction with bis(p-nitrophenyl)phosphoryl azide in DME, the use of 1.2 equiv. of 1 resulted in the production of azide with 80% ee (run 5), while product was obtained with less than 2% racemization and in good yield when 0.95 equiv. of 1 was used. 

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