Nitrenes toluene

The aforementioned mechanism is supported by the following experimental data. When oxime 13 was treated with Grignard reagent, 3% of the indole 15 was isolated, indicating the possible existence of nitrene intermediate 14. A 2-phenylazirine intermediate, on the other hand, has been isolated and characterized from the reaction under carefully controlled conditions (adding Grignard reagent to the oxime in toluene). ... 

Problems arise in the preparation of substituted l//-azepines with (alkoxycarbonyl)nitrenes as nitrene attack on a mono- or disubstituted benzene ring is not generally regioselective, and with toluene, 04 34-136139 144 o- and p-xy ienes,134-139 p-cresoi,134 chlorobenzene104-134 136 and biphenyl,104 136 mixtures of 1//-azepine-1-carboxylates of undetermined composition are produced. 

Starting materials other than sulphonyl azides have been used as possible sources of sulphonyl nitrenes. The decomposition of the triethyl-ammonium salt of iV- -nitrobenzenesulphonoxybenzenesulphonamide (26) in methanol, ethanol, and aniline gave products derived from a Lossen-type rearrangement 20> (Scheme 3). It was felt that the rearrangement did not involve a free sulphonyl nitrene since, when the decomposition was carried out in toluene-methylene chloride or in benzene, no products (benzenesulphonamides) of substitution of the aromatic solvent nucleus were found (as are usually found with sulphonyl nitrenes from the thermal decomposition of the corresponding azides). On the other... 

On the other hand, thermolysis of ferrocenylsulpkonyl azide (14) in aliphatic solvents may lead to the predominant formation of the amide (16) 17>. A 48.4% yield of (16) was obtained from the thermolysis in cyclohexane while an 85.45% yield of 16 was formed in cyclohexene. Photolysis of 14 in these solvents led to lower yields of sulphonamide 32.2% in cyclohexane, 28.2% in cyclohexene. This suggests again that a metal-nitrene complex is an intermediate in the thermolysis of 14 since hydrogen-abstraction appears to be an important made of reaction for such sulphonyl nitrene-metal complexes. Thus, benzenesulphonamide was the main product (37%) in the copper-catalyzed decomposition of the azide in cyclohexane, and the yield was not decreased (in fact, it increased to 49%) in the presence of hydroquinone 34>. On the other hand, no toluene-sulphonamide was reported from the reaction of dichloramine-T and zinc in cyclohexane. 

Examples of such reactions are well known. Sloan, Breslow, and Renfrow found that both alkane and arenesulphonyl azides insert into the carbon-hydrogen bonds of saturated hydrocarbons 12>. Thus, 1-pentane,- 2-propane- and -toluene-sulphonyl nitrene inserted into cyclohexane to give 54, 60, and 58% yields of the corresponding IV-cyclohexylamide derivatives 8>. Similarly, 2-phenoxybenzene-, diphenyl sulphide-2-, and... 

Perez and co-workers reported the electron-deficient copper homoscorpionate catalyst TpBr3Cu(NCMe)-catalyzed nitrene insertion into C-H bonds of toluene, mesitylene, and cyclohexane, which are very unreactive substrates (Equations (100)—(102)). In contrast to the former reports, they obtained very high yields for these products. 

Azidopyrazoles of type 22 extrude nitrogen upon heating (toluene, 95 °Q to give the corresponding nitrenes, which immediately rearrange to produce a mixture of furans and pyrazoles <99JOC2814>. 

Formation of the product of formal insertion of nitrene 16e into the aryl and benzylic CH-bonds of toluene was observed upon photolysis of 15e in toluene ... 

Abramovitch, Challand, and Yamada322 added thermally DMAD to 2-azido-3,4,5,6-tetrachloropyridine (172) and obtained 85% of the 1,2,3-triazole derivative (173), with no evidence for the generation of the nitrene. A one-step furopyridine synthesis of a mixture of 175 and 176 is achieved by treating the 1-oxide 174 with DMAD in hot toluene, rearrangements having taken place.323... 

Another attractive method for E ring formation featured an intramolecular [2+3]cycloaddition of an azide moiety, emanating from the indole 3-position via a two-carbon linker, to, now, an electron-rich version of the C15-C16 double bond.19 The cycloaddition precursor 10 was made via 9, in turn assembled by regioselective cocylization of protected methoxyacetylene (Scheme 5). In a puzzling turn of events, thermolysis of the azide product in toluene at moderate temperature (to minimize nitrene formation) and in low concentration (to suppress intermolecular reactions) produced the two oxidized pentacyclic products 11 and 12 in a 2 1 ratio. Performing the reaction in a more polar solvent (DMF, 80 °C, 7 d) altered the ratio to 5 1.20... 

Thermolysis of 2-benzoyl-2-halo-2//-azirines 102 in toluene under reflux affords 4-haloisoxazoles 104 in high yields via an intermediate nitrene 103 (Scheme 56) <2002S605>. 

Simple 3-subsdtuted indoles can be formed in high yield by heating p-azidostyrenes in solution. Thus heating CHNa in toluene gives 3-phenylindole in 82% yield. The reaction has recently been extended to the preparation of 3,4-bridged indoles (Scheme 13),and since the precursor azides are prepared from readily available cyclic ketones, the nitrene route represents a useful entry to these somewhat inaccessible bridged indoles. 

The ring contraction of 2-azido-3-methylquinoxaline 1,4-dioxide (1) to 2 is believed to proceed by an assisted non-nitrene reaction because it proceeds in solution below 100 °C. If the reaction is conducted in toluene at 90 C, however, only compound 3 is formed in 94% yield. ... 

Benzo[c]cinnoline 5-oxide is formed when 2-azido-2 -nitrosobiphenyl is heated in toluene, possibly by cyelization to the dipolar intermediate (12), followed by elimination of nitrogen [Eq. (6)], or via 2-nitrosobiphenyl-2 -nitrene. The quantitative eonversion of 2,2 -diazidobiphenyl into benzo-[c] cinnoline by low-temperature photolysis was argued to provide evidence for a stepwise process through the azidonitrene and the dinitrene [Eq. (7)]. ... 

Studies of the photodecomposition of azido derivatives of PCB have attracted interest because of their potential use as photolabels in intracellular distribution studies.Polyfluorinated aryl azides are also of current interest as new reagents for photoaffinity labelling. The major products of photolysis of methyl 4-azidotetrafluorobenzoate in cyclohexane or diethylamine, for example, arise by insertion, a property which enhances its use in labelling. Singlet pentafluorophenyl nitrene, formed in an analogous fashion on irradiation of pentafluorophenyl azide, can be trapped by toluene as the insertion products (79) and (80). °... 

Further examples of the formation of annelated pyridines by nitrene insertion into methyl groups were obtained by pyrolysis of arylvinyl azides in toluene solution (Scheme 5).40 Evidence that these reactions also take place via initially formed azirines was secured by the isolation of 26 from the pyrolysis of 25.40... 

Merrill and Unruh 35> described the preparation of azidophthalate esters of poly (vinyl alcohol). They found that the reaction of a nitrene with poly(vinyl toluene) was parallel to that of ethyl benzene in that side-chain hydrogen atom abstraction took place. -Carboxyphenylazide gave p, p -dicarboxyazobenzene and nitrogen on irradiation in the crystalline form 3S>. 

Abramovitch et al. [97] demonstrated that the pentafluorophenyl nitrene intermediate generated from treatment of nitroso compound 13 with triethyl-phosphite reacted with electron rich aromatics. Adducts were formed with benzene, toluene, anisole, and mesitylene in modest yield. 

Dilution of toluene with the inert solvent methylene chloride was attempted in an effort to extend the singlet nitrene lifetime and enhance the yield of triplet nitrene [104]. Dilution, however, did not change the ratio of aryl C-H to benzyl C-H insertion products formed, instead the yield of all volatile products decreased at the expense of tar formation. Dilution with CH2C12 did not increase the yield of triplet nitrene derived products such as C6F5NH2 and decafluoroazobenzene, thus the yield of triplet phenyl nitrene is negligible (Table 7) in methylene chloride. The results can be understood with the aid of Scheme 10, which is identical to the mechanistic hypotheses written for parent phenyl azide (Scheme 7). 

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