Methoxycarbonyl anion equivalents

A general synthesis of a-hydroxy esters is based on 2-ethylthio-l,3-benzodithiole which serves as a methoxycarbonyl anion equivalent. Thus reaction of the lithium compound (216) with ketones followed by treatment with mercury perchlorate in methanol leads to the formation of a-hydroxy acid derivatives (217) (81SC209). 

Lithio-2-ethylthio-l,3-benzodithiole (57) is a methoxycarbonyl anion equivalent, which reacts with various aromatic ketones to give a-hydroxy-esters in yields between 74 and 95% after desulphurization (Scheme 40). ... 

Methoxycarbonyl Anion Equivalent. The alkylation of lithiophenylthiobis(trimethylsilyl)methane with an alkyl halide, followed by electrochemical oxidation of the resulting thiobis-(sUane), provides a homologated methyl ester (eq 7). The electrochemical oxidation, due to its mild nature, can be tolerated by a wide variety of functional groups. 

Miura and coworkers and Akutsu and coworkers reacted a copolymer of styrene and 2,5-bis(methoxycarbonyl-l-hexene (87) with LDA to yield a polyenolate (88), which was active in the anionic polymerization of MMA (equation 67). When less than 1 equivalent (0.75) of LDA relative to the ester groups was used, the graft copolymer 89 was formed . When more than 1 equivalent of LDA was used, the molecular weight distribution was bimodal. Indeed, a mixture of homopolymer (PMMA) and graft copolymer (89) was formed merely because LDA is also prone to initiate the anionic polymerization of MMA . It was ascertained that the styrene units of the copolymer were not involved in the grafting reaction. ... 

The reaction of the l-(diaminocyclopropenyliumyl)pyridinium dication 30 with two equivalents of potassium pentakis(methoxycarbonyl)cyclopentadienide (31) also afforded the ionic salt 32 of 1 2 composition, whose structure was determined by X-ray crystallography. On the other hand, the reaction of 30 with the lithium salt of the 7,7,8,8-tetracyanoquinodimethane adical anion 33 resulted in covalent bond formation giving the substituted bis(cyclo-propenylium) dication 34. °... 

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