Radical reactions sulfonates

Besides radical additions to unsaturated C—C bonds (Section III.B.l) and sulfene reactions (see above), sulfonyl halides are able to furnish sulfones by nucleophilic substitution of halide by appropriate C-nucleophiles. Undesired radical reactions are suppressed by avoiding heat, irradiation, radical initiators, transition-element ion catalysis, and unsuitable halogens. However, a second type of undesired reaction can occur by transfer of halogen instead of sulfonyl groups283-286 (which becomes the main reaction, e.g. with sulfuryl chloride). Normally, both types of undesired side-reaction can be avoided by utilizing sulfonyl fluorides. 

The free-radical reaction may be equally initiated by photoactivated sulfur dioxide (3S02)442 (equation 79). On the other hand, polysulfones are obtained by radical copolymerization of appropriate olefins with sulfur dioxide443-449, and similarly, uptake of sulfur dioxide by a radical-pair formed by nitrogen extrusion from an azo compound yields the corresponding sulfone450 (equation 80). Correspondingly, alkylbenzenes, dibenzoyl peroxide, and sulfur dioxide yield sulfones under thermal conditions451... 

Beside these free radical reactions of sulfur dioxide, its electrophilic reactions generating sulfinates with organometallic compounds453,454 or sulfinic acids with arenes under Friedel-Crafts conditions455 are well known. To complete these three-component syntheses, the sulfinates prepared first are transformed to sulfones by reactions with appropriate electrophiles, discussed earlier in this chapter, i.e. equation 82. 

In a study aimed at the identification of products of free radical reactions with polystyrene- and aromatic-based PEMs using model compounds, Hiibner and Roduner observed the addition of free radicals to the aromatic rings, preferentially in the ortho position to alkyl- and RO-substituents (in polystyrene- and aromatic-based PEMs, the para position is blocked by the presence of the sulfonic acid group). This study demonstrated the combined ortho-activation by these substituents and the meta-directing effect... 

A graft terpolymer of lignin has been made by free radical reaction of 2-propenamide and 2,2-dimethyl-3-amino-4-oxohex-5-ene-l-sulfonic acid in... 

The 2,3-double bond in benzo[6]thiophene-1,1-dioxides undergoes addition reactions with nucleophiles in a manner comparable to that of other a,/9-unsaturated sulfones no aromatic properties are detectable in this way for the thiophene ring.718-723 For example, thiophenol and p-thiocresol give the adducts (340 R = H or Me) in the presence of base.723 However, if the aryl mercaptan and the sulfone are heated together, a radical reaction occurs to give the corresponding 2-substituted compound.723 In contrast to the behavior of aryl mercap-... 

A typical cooked-beef flavor deterioration sample was prepared as described in Beef Preparation section to observe changes in key sulfur marker compounds over a period of 0-, 2-, 4-, and 7-day storage. Sulfur markers, methional, methyl sulfone, and benzothiazole were compared with benzothiophene as internal standard to follow the course of free radical reactions taking place in the stored cooked-beef. Results are plotted in... 

Tin-lithium exchange has been widely used in synthesis, particularly to form stereodefined organolithiums (section 5.2.1). For example, Sinay used a radical reaction to displace the sulfone from the glycoside 161, substituting for a BUjSn- group. Tin-lithium exchange of 162 gave a vinyllithium 163 which reacted with electrophiles to yield products such as 164.132... 

Table 3.4. Radical transfer reactions involving OH radicals and sulfonated substrates demonstrated by endgroup analysis 1401...

Citterio, A., Gentile, A., Minisci, F., Serravalle, M., Ventura, S. Polar effects in free-radical reactions. Carbamoylation and a-N-amidoalkylation of heteroaromatic bases by amides and hydroxylamine-O-sulfonic acid. J. Org. Chem. 1984,49, 3364-3367. 

Asymmetric dihydroxylation of trifluoromethylalkenes is also useful for construction of enantio-enriched trifluoromethylated diols usable for trifluoromethylated amino acids with chiral hydroxyl group. Thus, Sharpless AD reaction of 16 provides diol 17 with excellent enantioselectivity. Regioselective and stereospecific replacement of the sulfonate moiety in 18 with azide ion enables the introduction of nitrogen functionality. A series of well-known chemical transformation of 19 leads to 4,4,4-trifluorothreonine 20 (see Scheme 9.6) [16]. Dehydroxylative-hydrogenation of 21 by radical reaction via thiocarbonate and subsequent chemical transformation synthesize enantio-enriched (S)-2-amino-4,4,4-trifluoro-butanoic acid 22 [16]. Both enantiomers of 20 and 22 were prepared in a similar manner from (2R,3S)-diol of 17. 

Reductive Desulfonylations by Tin Hydrides. Reductive desulfonylation of allyl, vinyl, and a-functionalized sulfones can be carried out employing tin hydrides. This radical reaction is usually promoted thermally or photochemically and provides organotin derivatives as intermediates which are finally subjected to protonolysis (Eq. 32). Both steps can be carried out in one pot employing catalytic amounts of tin. 

A variety of atom transfer radical reactions involving addition of halo, phenyl-seleno, and phenylthio sulfonates have been developed. In these reactions, it is believed that the sulfonyl radical attacks the olefin, and the halogen or arylchalcogen... 

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