Department of Chemistry, Fudan University, 220 Handan Road, Shanghai, Shanghai 200433, China
J. Chem. Educ., Article ASAP
DOI: 10.1021/ed500292q
Publication Date (Web): January 23, 2015
Copyright © 2015 The American Chemical Society and Division of Chemical Education, Inc.
*E-mail: sunxingwen@fudan.edu.cn.
Diastereoselective Allylation of N-tert-Butanesulfinyl Imines: An Asymmetric Synthesis Experiment for the Undergraduate Organic Laboratory
An asymmetric synthetic experiment that encompasses both diastereoselectivity and enantioselectivity is described. In this experiment, Zn-mediated allylation of an (R)-N-tert-butanesulfinyl imine is first performed to obtain either diastereomer using two different solvent systems, followed by oxidation of the homoallylic N-tert-butanesulfinyl amines, which gives either enantiomer of the corresponding products. Purification by flash column chromatography is required at the final step and the desired products are isolated in good overall yields. The diastereomeric ratio (dr) of the allylation products is determined by 1H and19F NMR spectroscopy, while the enantiomeric excess (ee) of the final products is measured by chiral HPLC. Overall, this experiment can be carried out with readily accessible reagents under mild conditions. Moreover, it enables students to learn the differences between enantiomers and diastereomers, the determination of ee and dr regarding optical compounds using HPLC and NMR spectroscopy, and how a reversal of stereochemical outcome is realized simply by tuning the reaction solvent.
NMR analyses of the homoallylic N-tert-butanesulfinyl amines obtained from the THF system (left) and the DMF system (right).
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