Sulfones carbanions

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. 

Examples of 1,13- and 1,14-asymmetric inductions are reported in the case of the addition of sulfone carbanions to benzaldehyde.119... 

Reactions of /ra .v-/i-styryl sulfone carbanion ( /i) - CIC H S O 2 CH=C H Ph, with PhCHO, CH3CN, and A1NO2 under phase-transfer conditions have been explored.59... 

Amatore C, Thiebault A, Verpeaux J-N (1989) Unexpected single electron-transfer catalyzed cyclization of prenyl sufore dimer - evidence for radical-anion coupling in the outer-sphere oxidation of prenyl sulfone carbanion. J Chem Soc Chem Commun 20 1543-1545... 

The unusual [2,l]oxazine (27) is formed by an interesting variation of vicarious nucleophilic substitution in the reaction of 1 -chloropropyl-/ -tolyl sulfone carbanion with 5-nitroquinoline (Equation (17)) <86LA69>. 

The mechanism and steric course of a nucleophilic addition reaction to an a,/l-unsaturated sulfone, such as 5, is, as expected, substantially controlled by the relative thermodynamic stability of the transition state due to the steric and electronic environment around the planar a-sulfone carbanion l0°. 

A modification of vitamin A synthesis was reported recently,using addition of allylic sulfone carbanion to aldehyde followed by a basic double elimination of the resulting -alkoxy sulfone with excellent stereocontrol (Scheme 64). 

When the sulfone has an a-halo substituent, formation of the carbanion is often accompanied by loss of the SO2 moiety via the so-called Ramberg-Backlund reaction.335 An illustration is the conversion of 1-bromo-ethyl ethyl sulfone (327) to 2-butene.336 Initial reaction with potassium hydroxide generated the sulfone carbanion (328), which displaced bromide intramolecularly to give an episulfone (329). Under the reaction conditions, 329 lost sulfur dioxide (SO2) to give the alkene. Meyers introduced a modification of this reaction in which the sulfone was converted directly to the alkene without isolating the a-halosulfone, using KOH in CCl4.337,338 Sulfuryl chloride and bromine can also be used.338... 

Sulfonate carbanions have been used less extensively than sulfone, sulfoxide, and sulfide carbanions. Sulfonates are good leaving groups and subject to nucleophilic displacement or elimination in the presence of the bases required to generate the carbanion. Cyclic sulfonates (sultones such as 330) have been alkylated via... 

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. 

SCHEME 11.48 Cine versus VNS in the reaction of a-chloropropylphenyl sulfone carbanion with... 

Furans. Timm and coworkers have devised a strategy to synthesize 2,5-disubstituted furans using sulfone carbanion-mediated solid support as a traceless linker (Scheme 12.16). They demonstrated the usefulness of the highly reactive basic carbanionic species of the... 

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