Easy Access to 9-Epimers of Cinchona Alkaloids: One-Pot Inversion by Mitsunobu Esterification-Saponification

Abstract

Cinchona alkaloids were efficiently converted into their 9-epi diastereomers. The applied one-pot procedure was based on the Mitsunobu esterification with 4-nitrobenzoic acid followed by in situ saponification of the ester. This method requires only one column chromatography, easily separating the epi-isomer from the native alkaloid and the Mitsunobu byproducts. The procedure gives higher yields and is operationally simpler than the previously used stereoselective hydrolysis of the corresponding sulfonic acid esters.

Key words

cinchona alkaloids - Mitsunobu reaction - inversion - alcohols - chiral pool

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