Ethyl acetate enantioselective transesterification

The key structural feature of POST-1 - the presence of dangling pyridine groups in the channels - affords a unique opportunity to perform asymmetric heterogeneous catalysis. Thus, potentially, any base catalyzed reactions (e.g., esterification or hydrolysis) can be performed with POST-1. Moreover, chiral pores should induce a degree of enantioselectivity in the final product mixture. The catalytic activity of POST-1 in the transesterification reaction was examined. Although the reaction of 16 and ethanol in the presence of POST-1 in carbon tetrachloride produced ethyl acetate in 11% yield, little or no transesterification occured without POST-1 or with the iV-methylated POST-1 (Sect. 2.2). The post chemical modification of the pyridine groups in POST-1 proves the role of free pyridine moiety in transesterification reaction. Transesterification of ester 16 with bulkier alcohols such as isobutanol, neopentanol, and 3,3,3-triphenyl-l-propanol occurs at a much slower rate under otherwise identical reaction conditions. Such size selectivity suggests that catalysis mainly occurs in the channels. 

Scheme 14 Ethyl acetate as reagent and solvent of an enantioselective transesterification.

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