Radical initiators, addition sulfonyl halides

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 additions of sulfonyl halides to alkenes, catalyzed by light or typical chemical radical initiators (In), were first investigated in the 1950s69. The products which are / -halo sulfones (22) were obtained via a chain reaction in which RSO j acts as the chain carrier, namely61-62,70,71... 

Sulfonyl halides, particularly arenesulfonyl halides, can afford radical species much faster than carbon halides by the assistance of a metal complex and efficiently add to olefins with little dimerization of sulfonyl radicals in comparison to carbon-centered radicals. Another feature of the compounds is that there is little effect of the substituents on the rate of addition to an olefin. These properties make sulfonyl halides an efficient and universal series of initiators for the metal-catalyzed living radical polymerizations of various monomers including methacrylates, acrylates, and styrenes (Figure g). 52.175-177... 

In addition to the carbon-centered radical initiators, arenesulfonyl halides are simple and efficient functionalized initiators by introducing a variety of functional termini conjugation between the aryl and the sulfonyl groups is absent (FI-51 to FI-58 Figure 14).175 Typically, a series of monosubstituted derivatives (FI-51) are commercially available and afford hydroxyl, carboxyl, nitro, and halo groups in living... 

The initiation step in ATRP involves homolytic cleavage of an activated halogen-containing compound and subsequent addition of this radical to the monomer as shown in Scheme 23. The fragment that is retained at the a-end of the polymer can be composed of functional groups that are tolerant to the ATRP catalyst and propagating chain end. Two main classes of functionalized initiators have been reported, activated alkyl halides and sulfonyl halides. 

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