Aryl carbanions alkylation

The rearrangement of an ether 1 when treated with a strong base, e.g. an organo-lithium compound RLi, to give an alcohol 3 via the intermediate a-metallated ether 2, is called the Wittig rearrangement. The product obtained is a secondary or tertiary alcohol. R R can be alkyl, aryl and vinyl. Especially suitable substrates are ethers where the intermediate carbanion can be stabilized by one of the substituents R R e.g. benzyl or allyl ethers. 

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

It occurs with the alkyls, aryls or acetylides of metals more electropositive than magnesium, but including Grignard reagents, and is often carried out by adding a solution of the organometallic compound in an inert solvent to a large excess of powdered, solid C02 it is a particularly useful method for the preparation of acetylenic acids. The Kolbe-Schmidt reaction (p. 291) is another example of carbanion carbonation. 

Acylation of ketones with esters requires the presence of a strong base under anhydrous conditions. Ketones where only one unique mesomeric carbanion is formed (e.g. symmetrical ketones or alkyl aryl ketones) yield a single regio-isomer. The reaction is illustrated by the formation of benzoylacetone from acetophenone and ethyl acetate (Expt 5.103), and may be outlined mechanistically as follows ... 

An alkyl/aryl ER may, in a few extreme cases, be considered to contain R carbanions alkyls/aryls of clearly covalent character behave chemically as sources of R if E is of lower electronegativity than C. There is a decrease in basicity along the isoelectronic series ... 

Reaction of the a-carbanion of an alkyl aryl sulfoxide (RCH2SOAr) with aldehydes may give four dia-stereomers. In general, the reaction is highly diastereoselective with respect to the a-sulEnyl carbon, but poorly diastereofacially selective with respect to attack on the carbonyl component. In fact, the a-carb-anion (31) of benzyl t-butyl sulfoxide adds to an aldehyde to produce only two diastereomers (32a) and (32b). As shown in Scheme 10, the selectivity increases when the counterion is A transition state structure (33) is proposed to account for the anti stereoselection. Addition of the dianion of (/ )-3-(p-to-lylsulfinyOptopionic acid (34) to aldehydes affords two main diasteieoisomeric 3 (p-tolylsulfinyl)-y-lac-tones (35 R = Ph and Bu. ca. 60 40). These isomers (35) were separated by chromatography, and their... 

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