Sulphonyl azides

The production of the nitrenes from a variety of sources has been reported, the most common of which are the sulphonyl azides. 

Uncatalyzed thermal decomposition of sulphonyl azides is believed to give nitrene intermediates and nitrogen, in general ... 

More recent work 8> shows that the S—N bond can be cleaved by hydroperoxides and that aromatic sulphonyl azides only undergo free radical thermal decomposition if a source of radicals is provided. Some light on the nature of the radical transfer agent has recently been shed by the observation 14> that dodecyl azides are formed (2.3%) in the thermolysis of mesitylene-2-sulphonyl azide (3) at 150 °C in w-dodecane under nitrogen. It seems likely that a dodecyl radical is produced by hydrogen abstraction by the triplet nitrene (5) [mesitylene-2-sulphonamide was also formed (1.1%)] which then attacks undecomposed sulphonyl azide... 

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-... 

Photolysis of sulphonyl azides in dimethyl sulphoxide with 2537 A light gives IV-sulphonylsulphoximines 12 in 15—50% yield 5>. The reaction was formulated as going via a nitrene intermediate which was trapped by the nucleophilic solvent... 

Though the intermediacy of nitrenes is likely in these reactions, the possibility of prior complexing of the sulphonyl azide with the solvent... 

Ferrous chloride-hydrochloric acid mixtures catalyzed the thermal decomposition of sulphonyl azides in isopropyl alcohol to give occasionally almost quantitative yields of sulphonamide and acetone, and the molar ratio of azide consumed to ferric chloride formed was typically of the order of 20 to 1 21>. 

In contrast to the problems encountered on photolysis of alkyl- and aryl-sulphonyl azides, we have found that ferrocenylsulphonyl azide 74 is smoothly decomposed by 3500 A light in cyclohexane or in benzene to give ferrocene 15, ferrocenylsulphonamide 16 and the novel bridged [2]ferrocenophanethiazine 1,1-dioxide 17 24>. The yield of 17 varied with the nature of the solvent, being 13.3% in cyclohexane, 67% in benzene, and zero in dimethyl sulphoxide or DMSO/benzene 25>. 

Despite the volume of work concerned with metal-catalyzed decomposition of diazo compounds and carbenoid reactions 28>, relatively little work has been reported on the metal-catalyzed decomposition of sulphonyl azides. Some metal-aryl nitrene complexes have recently been isolated 29 31>. Nitro compounds have also been reduced to nitrene metal complexes with transition metal oxalates 32K... 

Dimethyl sulphoxide (amounting to slightly more than equimolar with azide and less than 1% overall concentration in solution in methanol) accelerates the copper-catalyzed decomposition and the only product formed (97%) is the sulphoximine (21). Even in the absence of copper, DMSO and benzenesulphonyl azide were found to undergo a slow reaction in boiling methanol to give 21 (< 40%). It was suggested33) that the sulphonyl azide itself (slow) or the copper complex 24 (fast)... 

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... 

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>. 

When mesitylene-2-sulphonyl azide (3) is heated to 150 °C in n-dodecane, a Curtius-type rearrangement of the nitrene (4) occurs as discussed in Section 2.1 i to give 2,4,6-trimethylaniline and the hexa-methylazobenzene 14>. A similar result has now been observed by a careful analysis of the thermolysis products of durene-3-sulphonyl azide in w-dodecane at 150 °C. The amine is definitely formed but the azo-compound could barely be detected 13>. 

Aromatic substitution by sulphonyl azides has been applied to the synthesis of cyclic sulphonamides not as readily available by other methods 16h For example, thermolysis of biphenyl-2-sulphonyl azide (60) in w-dodecane or in cyclohexane 78> at 150 °C gives high yields (partic-... 

Method A The sulphonyl azide (50 mmol), PhH (200 g), NaHCO, (1.68 g) and Adogen (0.22 g, 5 mmol) are heated in an autoclave at 125°C for 3 h. The cooled reaction mixture is filtered, washed well with H,0, dried (Na2S04), and evaporated to yield the azepine, which is purified by chromatography on alumina. 

Reaction of toluene-p-sulphonyl azide (RN3) with [M(NO)(CO)(PPh3)2] (M = Rh or lr) in benzene has afforded urea derivatives of the type [M(NO)(PPh3)2 (RNCONR)] (38).147 The related compounds [RhCl(PPh3)2(RNCONR)] were... 

An analogous sequence leads to ynamino phosphines 50 (89) which are particularly versatile precursors of push-pull phosphorylated ynamines 51-54 through subsequent oxydation with hydrogen peroxide, elemental sulphur, selenium and sulphonyl azides 143). 

The reaction between sulphonyl azides and Grignard reagents also leads to stable triazenes which are similarly degraded with alkali to aryl azides (equation 125). This reaction constitutes not... 

Sulphonyl azides have been analysed by two processes release of nitrogen by reaction with triphenylphosphine and release of iodine by reaction with potassium iodide-acetic acid . 

The Russian workers claim that substituents on the azido group which increase the asymmetry, presumably by changing the equivalence of the bonding, shift the bands in question to higher frequency. They also suggest that this asymmetric stretching band for aromatic sulphonyl azides can be correlated by a Hammett Opp relationship where p has a small value. (They find the ultraviolet spectral parameters responding in similar fashion.)... 

Sulphonyl azides have asymmetric stretching frequencies at the high end of the range mentioned earlier (2140 cm ). The success of an early preparation of methanesulphonyl azidewas characterized by i.r. absorption at 2137 cm" A 1964 study of infrared spectra in the series of compounds represented by Formula 1, showed that the frequency of absorption (2140 cm ) was quite constant. 

The long wavelength band (285 nm) is not found in sulphonyl azides . Perhaps, due to its low intensity it is hidden under the tail of other intense but shorter wavelength absorptions. 

---