Resumen de Diastereoselective Allylation of N-tert-Butanesulfinyl Imines: An Asymmetric Synthesis Experiment for the Undergraduate Organic Laboratory
Xiao-Yang Chen, Li-Sen Sun, Xiang Gao, Xing-Wen Sun
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 and 19F 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.
