Imidazole catalyzed transesterification

Fluorenylmethyl esters of A -protected amino acids were prepared using the DCC/ DMAP method (50-89% yield) or by imidazole-catalyzed transesterification of... 

The mechanism of imidazole-2-ylidene-catalyzed transesterification has been studied using B3LYP DFT (Scheme 10). The reaction is predicted to involve neutral tetrahedral intermediates, TSl and ATSl, in which the catalyst imidazol-2-ylidene facilitates proton transfer from alcohol to the carbonyl oxygen by forming the tetrahedral intermediate TD <2005TL6265, 2005OL2453>. 

Benzyl acetate is usually used as jasmine flavor. It is produced in industry through the add-catalyzed esterification of acetic acid and benzyl alcohol. This is a non-green low-yield route. So Huang et al. made an attempt to biosynthesize benzyl acetate via hpase-catalyzed transesterification of vinyl acetate with benzyl alcohol in water-in-[Bmim][PFg] microemulsion stabiHzed by AOT and Triton X-100. Owing to the high dispersion of lipase, large interface, removal of the byproduct, and activation of imidazole cation, a maximum yield of 94% was obtained [99] (Figure 15.29). 

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