P552: Establishing the absolute configuration of chiral secondary alcohols using the Competing Enantioselective Conversion (CEC) method: Visualizing enantioselectivity using thin-layer chromatography
Effective methods to demonstrate the importance of chirality in an undergraduate laboratory setting are hindered by the difficulty of experimentally differentiating enantiomers of a compound with easily accessible resources. We report an experiment to establish the absolute configuration of enantioenriched secondary alcohols by comparing two reactions, each containing a pair of chiral molecules, using the Competing Enantioselective Conversion (CEC) method (1). An enantioenriched chiral secondary alcohol is reacted with each enantiomer of a chiral acylating agent in separate reactions. These two reactions result in one case where the secondary alcohol is “matched” with one enantiomer of the chiral acylating reagent, producing a fast reaction, and one case where the same alcohol is “mismatched” with the other enantiomer of the chiral acylating reagent, producing a slower reaction over the same time period. These different rates are visualized via thin-layer chromatography (TLC). By identifying the faster reaction, the absolute configuration of the starting alcohol is assigned via a mnemonic. The experiment has been conducted with over 1,000 students (2). This laboratory experiment is simple to execute at both small and large schools, with commercially available reagents and materials. (1) Wagner, A. J.; Rychnovsky, S. D. J. Org. Chem. 2013, 78, 4594−4598. (2) Wagner, A. J.; Miller, S. M.; Nguyen, S.; Lee, G. Y.; Rychnovsky, S. D.; Link, R. D. J. Chem. Educ., in press.