Transesterification imidazolium salts

Suzuki and co-workers first published on the topic of enantioselective transesterification in 2004 [140, 141]. This process exploits C -symmetric imidazolium salts with various substitutions. When vinyl propionate 281 acts as the acyl donor, ester 282 is isolated in 68% ee at 19% conversion, corresponding to an s value of 6.1 (Eq. 27). 

The lipase-catalysed enantioselective acylation of allylic alcohols in an ionic liquid solvent was demonstrated by Itoh et al. [16] (Fig. 7.7). They found that the acylation rate was strongly dependent on the counter anion of the imidazolium salt, while the lipase-catalysed acylation proceeded with high enantioseleclivity in all ionic liquid tested. Good results were obtained when the reaction was carried out in [bmimT [PFg ] or [bmun" ][BF ]. Other examples of kinetic resolution of allylic alcohols catalysed by lipases in ionic liquids were also reported by these authors [71, 72]. The transesterification of 5-phenyl-l-penten-3-ol under reduced pressure at 27 hPa and 40°C was carried out using methyl phenylthioacetate as acyl donor in [bmim+] [PF ] and [bdmim ][BF ], for obtaining the corresponding acylated compound in optically pure form [71], The acetylation of methyl mandelate catalysed by immobilised P5L in [bdmim ][BF ] is another example reported by these authors about the successful application of ionic liquids as reaction media in racemic resolutions... 

An ionic liquid also has vast possibilities because the hquid properties as a solvent can be altered by designing the molecular structure. There are a few reports of enzymatic ring-opening polymerization in ionic liquids. The hpase-catalyzed polymerization of e-CL was carried out in ionic solvents, such as the l-butyl-3-methyl-imidazolium salts [169]. In order to establish the compatibihty of enzymes with ionic liquids, the hpase-catalyzed transesterification of 2-hydroxymethyl-1,4-benzodioxane was studied [170]. 

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