Sulfonates metalation

Early recommendations for cross-linking CSM involved the use of divalent metal oxides to form metal sulfonate cross-links (24). The mechanism involves the hydrolysis of the sulfonyl chloride group with a carboxyHc acid, ie, stearic acid, which produces water at curing temperatures. 

Sulfonium ylides R2S=CR 2 [672,673] and metallated sulfones [674-676] can cyclopropanate simple alkenes upon catalysis with copper and nickel complexes (Table 3.6). Because of the increased nucleophilicity and basicity of these ylides, compared with diazoalkanes, these reagents are prone to numerous side-reactions,... 

The commercial products contain one chlorine atom per 2-3 repeat units and about one chlorosulfonyl group per 70 repeat units. The chlorosulfonyl groups allow the elastomer to be vulcanized with metal oxides such as lead or magnesium oxide by the formation of metal sulfonate linkages ... 

A drawback is that phosphonium sulfonate is not very hygroscopic, but it severely lowers the mechanically properties. On the other hand, alkali metal sulfonates exhibit excellent antistatic performance, but they are hygroscopic. 

Sulfonates such as mesylates or tosylates are readily prepared from alcohols under mild conditions, and are therefore attractive alternatives to halides as electrophiles. Although sulfonates often undergo clean displacement by nucleophiles, alternative reaction pathways are accessible to these intermediates, which can lead to unexpected results. If the nucleophile used is strongly basic, metalation instead of displacement of the sulfonate can occur. Some potential reactions of such metalated sulfonates include fragmentation into sulfenes and alcoholates, or into sulfmates and carbonyl compounds, or self-alkylation (Scheme4.15). 

It has been shown that it is possible to effectively reduce the flammability of many polymeric materials by using metal compounds in very low concentrations. Metals and their compounds may be included in the polymeric macrochains, either coordi-natively bonded to functional groups of the polymer or used as additives. For example optically transparent, low-flammability polycarbonates have been obtained by adding as little as 0.001 to 2 % by weight of alkali or alkaline earth metal sulfonates... 

The fusion of alkali metal sulfonates with alkali in the presence of some water is used both in the laboratory and in industry (Scheme 4.2). 

The authors suggest that the differences (a and b) reflect the stabiUty of the metalated sulfones as olefination efficiency is lower when the sulfone is prone to self condensation. 

Intramolecular opening of epoxides with a hetero-atom nucleophile promoted by a titanium salt is shown in Table 27. Intramolecular alkylation of an epoxide with a metalated sulfone enhanced by Ti(0-t-Pr)4 has also been reported to give a single cyclization product, as shown in Eq. (289) [650]. 

The use of aromatic sulfonates stems from their ability to assist the solution of organic substrates in an aqueous medium. This hydrotropic effect [270,450,451] is accentuated if a quarternary ammonium sulfonate, rather than an alkali metal sulfonate, is used. 

Olefins can be prepared from )5-hydroxysulfones [35]. The hydroxyfulsones are prepared by alkylation of metallated sulfones using various aldehydes [Eq. (28)]. Both magnesium and lithium sulfones were evaluated, and the magnesium sulfones had the... 

Alkyl phenyl sulfones (piCj,27) are nearly as acidic as esters hence they are readily deprotonated by n-BuLi, LDA in THF, or EtMgBr in THF to give a-metalated sulfones. Their reaction with aldehydes gives a mixture of diastereomeric P-phenylsul-fone alkoxide adducts. Reductive elimination of the benzenesulfinate moiety from the adduct to produce the alkene is usually slow. To minimize side reactions, the hydroxyl group is first converted to an acetate, benzoate, mesylate, or /7-toluenesul-fonate and then treated with an excess of sodium amalgam [Na(Hg), prepared by adding small pieces of sodium to mercury] in methanol to furnish the trans-dlk n P... 

By comparison with the Homer-Wittig reaction, the Julia alkenation has two principal assets. First, as the nucleophilic partner in the connective step (stage 2), sulfones are used, which are often more readily available and more easily purified than the corresponding phosphonium salts. Secondly, the 1,2-disub-stituted alkenes produced in the key reductive elimination step have predominantly ( )-stereochemistry. One detraction of the Julia alkenation is its length — it can be foiled at any one of the four stages. In practice, stage 2, the condensation of the metalated sulfone with the carbonyl, is usually the most problematic but in certain circumstances all of the stages have their pitfalls. These will be examined individually below. 

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