Halides, sulfonyl, addition

The original reaction procedures have steadily been extended and improved, and an overwhelming number of catalyst systems are now known. Besides aryl halides, many additional substrates, for example aryl triflates, diazonium salts, sulfonyl and aroyl halides, carboxylic and phosphonic acids, and even arenes have been used as... 

The main synthetic applications of sulfonyl radicals are based on the ability of these species to add to double and triple carbon-carbon bonds 197]. A large variety of sulfonyl radical precursors can be used including sulfonyl halides, sulfonyl cyanides, and sulfonyl thiocyanates. During the past decade the addition of selenosulfonates has been widespread. Meanwhile, the development of methodologies involving the oxidation of sulfinates has opened the way to new kinds of adducts resulting from oxidative termination. 

Aromatic acyl halides and sulfonyl halides undergo oxidative addition, followed by facile elimination of CO and SO2 to form arylpalladium complexes. Benzenediazonium salts are the most reactive source of arylpalladium complexes. 

TABLE 5. Survey of sulfonyl halide additions to unsaturated systems and hydrogen halide eliminations to unsaturated sulfones... 

Normally, reactive derivatives of sulfonic acids serve to transfer electrophilic sulfonyl groups259. The most frequently applied compounds of this type are sulfonyl halides, though they show an ambiguous reaction behavior (cf. Section III.B). This ambiguity is additionally enhanced by the structure of sulfonyl halides and by the reaction conditions in the course of electrophilic sulfonyl transfers. On the one hand, sulfonyl halides can displace halides by an addition-elimination mechanism on the other hand, as a consequence of the possibility of the formation of a carbanion a to the sulfonyl halide function, sulfenes can arise after halide elimination and show electrophilic as well as dipolarophilic properties. 

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. 

Addition of sulfonyl halides to olefins, allenes and acetylenes. . . 1104... 

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... 

The three steps 32-34 have been suggested77 to be equilibria, and the overall equilibrium must lie far to the left because no adduct 23 is found in the reaction mixture when the reaction of sulfonyl chloride with olefin is carried out in the absence of a tertiary amine. A second possible mechanism involving oxidative addition of the arenesulfonyl halide to form a ruthenium(IV) complex and subsequent reductive elimination of the ruthenium complex hydrochloride, [HRulvCl], was considered to be much less likely. 

In the thermal reaction of aliphatic and aromatic sulfonyl chlorides with acetylenes no adduct has been observed82. However, the light-catalyzed additions of sulfonyl iodides to acetylenes83 as well as the thermal addition of sulfonyl bromides to phenylacetylene84 to form 1 1 adducts have been shown to be stereoselective and to occur in good to excellent yields. The fact that the addition occurs in a trans manner forced the authors83,84 to suggest that chain transfer by the sulfonyl halide (k ) is much faster than isomerization of the intermediate vinyl radical (k2) (see Scheme 5). 

As a consequence of facile homolytic cleavages, sulfonyl halides (I > Br > Cl F unsuitable) are able to add to unsaturated C—C systems. To prevent (or reduce) competing polymerizations, the additions of sulfonyl chlorides have been recommended to be carried out in the presence of copper(I/II) salts (Asscher-Vofsi reaction ). Comprehensive surveys have been published on the resulting j8-halogeno sulfones (or their vinyloguous compounds) as well as on their dehalogenation products (vinyl sulfones, 1-sulfonyl-l, 3-dienes, etc.). Table 5 reviews a series of sulfonyl halide additions and facile hydrogen halide eliminations. 

The Smiles rearrangement 5-28 Addition of ArSSCl to alkenes 9-35 Oxidation of thiols 9-54 Reduction of sulfonyl halides... 

The Darzens reaction is the base-promoted generation of epoxides XIII from aldehydes (or ketones) XI and alkyl halides XII, the latter carrying an electron withdrawing group, for example the carbonyl, nitrile, or sulfonyl, in the a-position (Scheme 6.83) [188, 189]. It is, formally, addition of a carbene to the C=0 double bond (Scheme 6.83, path B) and thus complements oxygen atom transfer to olefins... 

A number of different polar and nonpolar covalent bonds are capable of undergoing the oxidative addition to M( ). The widely known substrates are C—X (X = halogen and pseudohalogen). Most frequently observed is the oxidative addition of organic halides of sp2 carbons, and the rate of addition decreases in the order C—I > C—Br >> C—Cl >>> C—F. Alkenyl halides, aryl halides, pseudohalides, acyl halides and sulfonyl halides undergo oxidative addition (eq. 2.1). 

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