Methylsulfonyl carbanion

Russell and coworkers147 had found that treatment of dimsyl anion 88 or of a similar methylsulfonyl carbanion with 1,2-, 1,3- and 1,4-dicarboxylic acid esters can give five- to seven-membered cyclic compounds. By this type of cyclization, they prepared ninhydrin hydrate 106 from diethyl phthalate148,149. 

Other carbanionic groups, such as acetylide ions, and ions derived from a-methylpyridines have also been used as nucleophiles. A particularly useful nucleophile is the methylsulfinyl carbanion (CH3SOCHJ), the conjugate base of DMSO, since the P-keto sulfoxide produced can easily be reduced to a methyl ketone (p. 549). The methylsulfonyl carbanion (CH3SO2CH2 ), the conjugate base of dimethyl sulfone, behaves similarly, and the product can be similarly reduced. Certain carboxylic esters, acyl halides, and DMF acylate 1,3-dithianes (see 10-10. )2008 Qxj(jatjye hydrolysis with NBS or NCS, a-keto aldehydes or a-... 

Reaction between carboxylic esters and methylsulfonyl carbanion... 

The chlorine atom and methylsulfonyl group at the 2-position are less reactive to carbanions than those at the 6-position, and the methylsulfonyl group is more reactive to carbanions than the chlorine atom at the 2-position in the purine ring, e.g. formation of 4. ... 

As far as the phenylsulfonyl substituent is concerned it has been demonstrated by means of recent 3-21G calculations by Bors and Streitwieser that in the methylsulfonyl-methyl anion 308 the dominating mechanism of carbanion stabilization can be described as a classical polarization involving the SO2 group and n-a orbital interactions. The carbanionic center is planar although d-p-7c conjugation is not an important factor in stabilizing the anion. 

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