Sulfones carbanions from

It should be mentioned here that if no other leaving group is present, sulfonyl can act as its own leaving group in hydroxide- or alkoxide-catalyzed elimination from sulfones. Carbanion formation is not involved in this but the promotion of the ionization of a C—H bond by the sulfonyl group is seen at the /1-carbon rather than the a-carbon, e.g. equation 21. 

An interesting new method for the conversion of [I, y-epoxy sulfones (82) to cyclo-alkenones (85) has been developed61. It includes the addition of alkyllithium to y-hydroxy-a,/ -unsaturated sulfones generated from 82 and the alkylation of sulfonyl carbanion thus formed. Oxidation of the resulting y-hydroxy sulfone to 84 followed by elimination of benzenesulfinic acid gives the desired product 85 in good yields (equation 72)61. 

The sulfonyl group is a key feature in the preparation of the unusually substituted dithiin sulfone (174) from dibenzyl sulfone. The acidic a-protons are abstracted with sodium hydride and the carbanionic intermediates react with carbon disulfide. The reaction is quenched with methyl iodide to give (174) in 17% yield (73BSF637). Another multisubstituted dithiin (175) is available from the reaction of diphenylthiirene dioxide with the ylide (176) (Scheme 21) but again the yield is low. However, the reaction is of particular interest in so far as the product mixture also contains a derivative of the rare oxathiin nucleus. Indeed of the three products isolated the oxathiin sulfone (177) is formed in marginally the highest yield (73BCJ667). 

From oxidative cleavage of 1,2-diols and 1,2-amino alcohols Dibutyltin oxide, 95 By reaction of alkyl halides with sulfur-stabilized carbanions Methylthiomethyl p-tolyl sulfone, 192 From reduction of carboxylic acids Vilsmeier reagent, 341 From terminal alkenes by addition reactions... 

The stability of the BTFP sulfonyl carbanions generated with a variety of bases including LDA, KHMDS, phosphazene bases (P4-t-Bu) and KOH-TBAB towards auto condensation was studied. It was shown that the sulfone recovery from the respective anions was higher than recovery of BT and PT sulfones. 

Other applications of carbanions a to a sulfone in total syntheses have recently been reported. Most of them used allylic sulfones or allylic halides. Two examples are reported here. In the synthesis of a precursor of cembranolides, a sulfone derived from geranyl bromide was coupled with an allylic alcohol epoxide (Scheme 65). An interesting point was that the coupling reaction gave high yields only when the lithiated sulfone was allowed to react with the epoxymagnesio alkoxide (the lithium salt of the epoxy alcohol did not react at all with the lithiated sulfone). 

Review. Bergbreiter and Killough have discussed the various uses of CsK, particularly in comparison with the reactions of the soluble analog sodium naphthalenide. Perhaps the most useful role of CsK is for the rapid formation of alkoxides from alcohols and of stabilized carbanions from carbonyl compounds. In these two reactions, it reacts more readily than potassium itself and can be separated from the products by filtration. The authors conclude that it has only limited value for reduction of alkyl and aryl halides and sulfonates, reactions accomplished more readily by other reagents. They also note that CeK can be regarded as a suitable reagent for reactions in which sodium naphthalenide is useful. 

It was subsequently shown that carbanions generated from substituted a-chloroalkanenitriles [15] and alkyl a-chloroalkanoates [16, 17], chloroalkyl oxazolines [18, 19], chloroform [20], etc., although they are much less stable than the model sulfone carbanion, are able to react with nitroarenes to give the VNS products. 

The reaction of 3-methoxy-1,2,4-triazine 1-oxide 20 with the carbanion generated from chloromethyl phenyl sulfone proceeds as the vicarious nucleophilic substitution (VNS) of hydrogen (Scheme 1, path B) via addition of the carbanion at position 5 of the heterocycle. Following base-induced elimination of HCl and protonation, 3-methoxy-5-phenylsulfonyl-1,2,4-triazine 4-oxides 65 result (88LA627). 

Thus, like a, /1-unsaturated ketones and sulfones, both thiirene dioxides and thiirene oxides are preferentially attacked by the less basic nucleophiles on the vinylic carbon atom2. This would lead to formally 1,4 Michael-type adducts and/or other products resulting from further transformations following the initial formation of the a-sulfonyl and a-sulfoxy carbanions. 

Sulfur-containing groups at an a-position stabilize carbanions. All these species, i.e., the a-sulfonyl 6281-102, a-sulfmyl 6346-80, a-sulfenyl 645,103,104 and a-sulfonio carbanions 65105-1 ancj those derived from sulfonates 66 and sulfonamides 6795 may retain their... 

Alkylation of carbanions derived from allyl aryl sulfones 236 with alkyl halides is known... 

Carbanions derived from allylic sulfones 309 reacted with cyclohexenone, giving mainly... 

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