Nitrenes sulphonyl

Sulphonyl a-hydrogens, acidity of 402-405 Sulphonylisoxazolines, reactions of 791 Sulphonylmercuration 172 Sulphonylmethanes, acidities of 592 Sulphonyl migration 169 Sulphonyl nitrenes 810 2-Sulphonyloxaziridines 72 Sulphonyloxiranes 169 synthesis of 639... 

While the e. s. r. evidence points strongly to a triplet ground state, it tells us nothing about the state the sulphonyl nitrene is in when it undergoes reaction. Evidence bearing upon the latter comes from a consideration of the nature and relative rates of the reactions undergone by sulphonyl nitrenes and of the products obtained therefrom. This is considered in some detail in Section 3.3. 

Evidence for the formation of alkyl and aryl radicals in some cases following loss of SO2 (Scheme 1) has been obtained. Thus, a small amount of M-pentane was formed in the decomposition of M-pentanesulphonyl azide in mineral oil ). Thermolysis of diphenyl sulphone-2-sulphonyl azide (8) in dodecane at 150 °C gave diphenyl sulphone 9 (27%) and diphenyl sulphone-2-sulphonamide 10 (9%) which arise by hydrogen abstraction by the aryl radical and sulphonyl nitrene, respectively. When this thermolysis was carried out in Freon E-4 at 150 °C, the products were diphenylene sulphone 77 (1.3%) (Pshorr-type cyclization product of the aryl radical) and 10 (1.5%) together with tars 16h Ferro-... 

Copper catalyzes the decomposition of sulphonyl azides in benzene very slowly. When methanesulphonyl azide was boiled under reflux in benzene solution in the presence of an excess of freshly reduced copper powder, some decomposition occurred to give methanesulphonamide and azide was recovered 78>. Transition metal complexes have been found to exert a marked effect upon the yields of products and isomer ratios formed in the thermal decomposition of methanesulphonyl azide in methyl benzoate and in benzotrifluoride 36>. These results will be discussed in detail in the section on the properties of sulphonyl nitrenes and singlet and triplet behaviour. A sulphonyl nitrene-iron complex has recently been isolated 37> and more on this species will be reported soon. 

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... 

The success of this reaction was ascribed to the solubility of the chlorozinc intermediate, whereas other chloramine-T derivatives (e.g. the sodium salt) are insoluble. An alternative non-nitrene pathway was not eliminated from consideration. On the other hand, no aromatic substitution or addition, characteristic of a free sulphonyl nitrene (see below), took place on treatment of jV,lV-dichloromethanesulphonamides with zinc powder in benzene in the cold or on heating. The only product isolated was that of hydrogen-abstraction, methanesulphonamide 42>, which appears to be more characteristic of the behaviour of a sulphonyl nitrene-metal complex 36,37). Photolysis of iV.iV-dichloromethanesulphonamide, or dichloramine-B, or dichloramine-T in benzene solution led to the formation of some unsubstituted sulphonamide and some chlorobenzene but no product of addition of a nitrene to benzene 19>. 

A copper-sulphonyl nitrene complex has been postulated as an intermediate in the reaction of chloramine-T with DMSO and with dioxan 45>. In the absence of copper powder, only a small yield of sulphoximine (6%) was obtained in DMSO. Again, no sulphonylaniline or azepine... 

Finally, a sulphonyl nitrene has been suggested as a possible intermediate in the reaction of benzenesulphonyl isocyanate with phenylmagnesi-um bromide at room temperature, to account for the formation of a 13% yield of vV-phenylbenzenesulphonamide 47>. 

The chemical reactions of sulphonyl nitrenes include hydrogen abstraction, insertion into aliphatic C—H bonds, aromatic substitution , addition to olefinic double bonds, trapping reactions with suitable nucleophiles, and Wolff-type rearrangement. Hydrogen-abstraction from saturated carbon atoms is usually considered to be a reaction typical of triplet... 

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... 

Only limited success was achieved in determining the relative reactivity of primary, secondary, and tertiary carbon-hydrogen bonds to sulphonyl nitrenes 8>. Insertion of p-toluenesulphonyl nitrene into 2-methylbutane gave a mixture of products which could not be completely resolved. The ratio of (primary) (secondary + tertiary) = [38 + 39 40 + 41] was 1.53, compared to a ratio of 5.6 for carbethoxynitrene58>, indicating the lowered selectivity of the sulphonyl nitrene relative to the carbethoxynitrene, as might be expected from the possible resonance stabilization of the latter species. 

No insertion product was observed on photolysis of ferrocenylsul-phonyl azide in cyclohexane or in cyclohexene 25>, suggesting that the reactive intermediate formed is the triplet sulphonyl nitrene. The fact that addition to the olefinic bond of cyclohexene takes place under these conditions 25> does not necessarily argue against this conclusion (vide infra). 

Sulphonyl nitrene-metal complexes also undergo insertion into aliphatic C—H bonds as witnessed by the insertion into dioxan on treatment with chloramine-T and copper 45> and into cyclohexane with di-chloramine-T and zinc 44> and into cyclohexene with benzenesulphonyl azide and copper 34> and with ferrocenylsulphonyl azide 25>. 

This is the best known of the reactions of sulphonyl nitrenes and a large number of examples were studied by Curtius and his coworkers. The first attempt to establish semi-quantitative correlations between the nature of the substituent and orientation of the entering group was made by... 

Xylene was found to be twice as reactive as benzene towards tosyl azide, and a benzene double bond eight times more reactive towards singlet sulphonyl nitrene than a carbon-hydrogen bond in cyclohexane 8>12>. 

Addition of carbethoxynitrenes to olefinic double bonds occurs readily. Addition of both the singlet and the triplet species can take place, the former stereospecifically, the latter not 49>. Additions of sulphonyl nitrenes to double bonds have not been demonstrated except in two instances in which metals were present. The reason is that either addition of the starting sulphonyl azide to the double bond occurs to give a triazoline that loses nitrogen and yields the same aziridine as would have been obtained by the direct addition of the nitrene to the olefin, or the double bond participates in the nitrogen elimination and a free nitrene is never involved 68>. The copper-catalyzed decomposition of benzenesulphonyl azide in cyclohexene did give the aziridine 56 (15%), which was formulated as an attack by the sulphonyl nitrene-copper complex on the double bond 24>. 

The intramolecular insertion of a sulphonyl nitrene into a side-chain methyl group to give 36 and 37 has already been mentioned, as has the intramolecular cyclization of ferrocenylsulphonyl azide to give the bridged ferrocene derivative (17). 

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