Radical benzenesulfonyl

Arising from studies of the photochemistry of benzenesulfonyl systems, extensive ab initio MO calculations have been made for various sulfonyl radicals and related species253. The STO-3G basis set, which includes d-type polarization functions on second-row atoms, was used. The inclusion of d orbitals on sulfur was found to be very... 

Benson17 has tried to collect some thermodynamic data based on a number of empirical rules for this class of radicals. He estimated heats of formation for HS02, MeSO 2) PhSO 2 and HOSO 2 as —42, —55, —37 and — 98kcalmor respectively. He also estimated a stabilization energy for the benzenesulfonyl radical of 14 kcal mol"1, which is very similar to that of the benzyl radical. However, recent kinetic studies18 (vide infra) have shown that arenesulfonyls are not appreciably stabilized relative to alkanesulfonyl radicals, in accord with the ESR studies. 

Waters61 have measured relative rates of p-toluenesulfonyl radical addition to substituted styrenes, deducing from the value of p + = — 0.50 in the Hammett plot that the sulfonyl radical has an electrophilic character (equation 21). Further indications that sulfonyl radicals are strongly electrophilic have been obtained by Takahara and coworkers62, who measured relative reactivities for the addition reactions of benzenesulfonyl radicals to various vinyl monomers and plotted rate constants versus Hammett s Alfrey-Price s e values these relative rates are spread over a wide range, for example, acrylonitrile (0.006), methyl methacrylate (0.08), styrene (1.00) and a-methylstyrene (3.21). The relative rates for the addition reaction of p-methylstyrene to styrene towards methane- and p-substituted benzenesulfonyl radicals are almost the same in accord with their type structure discussed earlier in this chapter. 

There is clear evidence that the addition of a sulfonyl radical to an olefin is a reversible reaction. This has been demonstrated for the case of but-2-ene, where cis-trans isomerization of the olefin accompanies addition63,64. Furthermore, 18a and 18b radicals generated by the reaction of Bu3Sn with erythro- and tfireo-2-bromo-3-(phenylsulfonyl)butane, respectively, eliminate benzenesulfonyl radicals to some extent, even at — 67 °C, to form 2-butenes in a non-stereospecific manner, providing also indication that the rotation about the central C—C bond is faster than the /1-cleavage process65. 

Ito and Matsuda studied the y-radiolysis of 2-methyltetrahydrofuran (MTHF) solutions of diphenyl sulfone and dibenzothiophene-S,S-dioxide (DBTSD) at 77 K. They found that the radical anions of these sulfone compounds are formed and have intense absorption bands at 1030 nm and 850 nm, respectively. The blue glassy solution of y-irradiated diphenyl sulfone has absorption bands at both 1030 nm and 360 nm while the absorption spectrum of the benzenesulfonyl radical formed by UV irradiation of diphenyl sulfone solution at 77 K showed only a peak at 382 nm. Gamma-irradiated phenyl methyl sulfone solution showed an absorption band only at 385 nm. Consequently the appearance of the absorption bands in 800-1030 nm of diphenyl sulfone and DBTSD may suggest that the unpaired electron is delocalized on two phenyl rings. The same authors studied the radiolysis of MTHF solutions of disulfones (diphenyl and dihexyl disulfones). They found a blue coloring of the solution by the y-radiolysis of diphenyl disulfone and dihexyl disulfone due to absorption peaks at 695 nm and 690 nm respectively, besides smaller absorptions at 300-400 nm. Comparing these results to the previous observation, that phenyl methyl sulfone solution absorbs only at 398 nm, results in the conclusion that the absorption band at 690 nm is due to the linked two sulfone moieties. The authors found that substituents on the phenyl ring lead to shifts in the absorption maxima of the... 

As depicted in Scheme 11, ylides 39 derived from 4-methyl-[l,2,3]triazolo[l,5- ]pyridine react with Michael acceptors, which, upon nucleophilic attack at C3 and ring opening, lead to nucleophilic displacement of nitrogen. The intermediate diradical led to a mixture of compounds, including alkenes and a cyclobutane derivative when methyl acrylate was used, and the indolizine 40 with methyl propiolate as the electrophile <1998T9785>. Heating 4-methyl triazolopyridine with benzenesulfonyl chloride in acetone also confirmed decomposition via a radical pathway. 

Since benzenesulfonyl peroxide was used as an initiator in polymerization reactions, it was thought that a free radical aromatic substitution of benzene by the benzenesulfonoxy radical takes place. A detailed study by Dannley and Knipple reveals that attachment of the sulfonoxy group derived from a bis(arylsulfonyl) peroxide to the aromatic ring occurs by electrophilic aromatic substitution (equation 5) °. 

Ollivier and Renaud built on his new ditin-mediated radical azidation with benzenesulfonyl azide [125] to introduce tandem intramolecular cyclization-azidation processes [126]. For example, iodoacetal 131 provides the corresponding tertiary azide 132 in high yield as a 3 2 mixture of endolexo diastereoisomers (Scheme 41). The necessify of using ditin reagents still constitutes a drawback in this method, as DLP-mediated tin-free reaction conditions failed due to an inefficient chain process. 

In this reaction, the benzenesulfonyl radical is produced, where its HF coupling constant had been obtained to be Algjx = 8.32 mT. Because the author s group had already observed the MFE in this reaction [10], this was one of the candidates for detecting the MIE of Indeed, Step et al. found the a value for the Si-enrichment observed for this reaction in the absence of an external magnetic field as listed in Table 9-2. 

In the selective removal of an allylic benzenesulfonyl group in the presence of an unactivated benzenesulfonyl group, it was found that indirect electrochemical reduction employing suitable electrogenerated radical anions as reducing agents increased the selectivity [165]. 

Several products are formed when phenylcyclopropane is irradiated in acetonitrile with added trifluoromethylsulfenyl chloride. The phenylpropane derivative (284) is one of the products and its formation can be rationalised by attack of a chlorine atom, formed by S-Cl bond fission, on the cyclopropane to yield the radical (285) which combines with a trifluoromethylthio radical to give the product. cw-Stereoselective addition of benzenesulfonyl bromide occurs to the tricycloheptane (286) on irradiation and the two products (287) and (288) are formed in a ratio of 3 1... 

Reactions. The thermal decomposition of benzenesulfonyl azide gives radicals which react with aromatic hydrocarbons to give products of amidation.1-3 Like phenyl azide, benzenesulfonyl azide undergoes addition reactions with strained double bonds. Thus it reacts with norbornene (1, bicyclo[2.2.1 ]-2-heptene) with loss of nitrogen to give the azetidine (2) in nearly quantitative yield.2 The reaction is considered to involve the intermediate (a). In contrast the reaction... 

The radical carbonylation of an alkyl iodide in the presence of Kim s sulfonyl oxime ethers [58, 59, 60] provides a new type of multicomponent coupling reaction where plural radical Cl synthons are consecutively combined [61]. In the transformation, allyltin was used to serve as a trap of benzenesulfonyl radical which converts sulfonyl radical to a tin radical, thus creating a chain. Scheme 14 illustrates such an example, where the product was easily dehydroxylated to give the corresponding tricarbonyl compound on treatment with zinc/AcOH. The radical acylation reaction by Kim s sulfonyl oxime ethers can be conducted under irradiation with the addition of hexamethylditin. This is an alternative path for achieving a similar transformation without the use of photolysis equipment. Scheme 15 illustrates several examples where carbon monoxide and Kim s sulfonyl oxime ethers are successfully combined to create new tandem radical reaction sequences [61],... 

Scheme 14. Use of allyltin as a trap for the benzenesulfonyl radical and a chain carrier...

Perfluoroalkyl radicals can be generated from perfluorosulfonyl chloride using RuCljCRPh,), as a catalyst. In the presence of 1-substituted pyrroles good yields of 2-perfluoroalkylpyrroles were obtained with N-substituents such as acetyl, benzenesulfonyl or trimethylsilyl. With tr/s-isopropylsilyl, however, 3-substitution was preferred. <94SC2049, 94JCS(P1)1339>... 

Fused indoles have been synthesized using various radical strategies. Some of the more renowned works include Ziegler s Photochemically-induced cyclization of aUcyl, vinyl, oxiranyl, and aziridinyl radicals [87-89], Chuang s benzenesulfonyl radical induced oxidative cyclization of l-(4-allylsulfonylbutyl)indole [90], and Moody s tin-mediated cyclization of l-co-iodoalkylindoles [91]. 

Addition to Unsaturated Compounds. Benzenesulfonyl bromide undergoes radical-mediated addition to alkenes and alkynes. Addition to alkenes leads to bromo sulfones, which undergo dehydrobromination to give vinyl sulfones (eq 3). ... 

Numerous studies have been devoted to the addition of RSO2X to olefins. The propagation steps for these chain processes are shown in Scheme 13. The main factors controlling the reactivity of sulfonyl radicals are polar effects and the reversibility of the addition. Sulfonyl radicals exhibit an electrophilic character with respect to addition to olefins [98]. Evidence for the reversibility came early from the observation of the isomerization of cis- and rran -2-butenes during their copolymerization with sulfur dioxide and their Cu(I)-mediated reaction with benzenesulfonyl chloride [99]. Therefore, the chain transfer of alky] adduct radica]s has to compete effectively with -elimination of sulfonyl radicals (see Scheme 13). Selenosulfonates, sulfonyl halides, and sulfonyl cyanides are the most popular substrates that meet this property. 

Radical Addition Reactions of Vinyltrimethylsilane. Reaction of the title reagent with benzenesulfonyl chloride under radical addition conditions provides ( )-l-phenylsulfonyl-2-trimethylsilylethylene (15), an acetylene equivalent in Diels-Alder reactions (eq 8). In similar fashion, thiophenol adds to vinyltrimethylsilane regioselectively.i Oxidation of the thiophe-... 

---