Medical observation chromatography

Asymmetric Alkylation. 4-Pseudoephedrine ([IS, 2S]-(+)) is a commodity chemical employed in over-the-counter medications with annual worldwide production in excess of 300 metric tons. The enantiomer, /-pseudoephedrine, is also readily available in bulk and is inexpensive. Pseudoephedrine has been shown to be highly effective as a chiral auxiliary in asymmetric alkylation reactions. Treatment of either enantiomer of pseudoephedrine with carboxylic acid chlorides and anhydrides leads to efficient and selective iV-acylation to form the corresponding tertiary amide derivatives (Table 1). Typically, the only by-product in the acylation reactions is a small amount (<5%) of the A,0-diacylated product, which is easily removed by crystallization or flash column chromatography. Because intramolecular 0- -N acyl transfer within pseudoephedrine 3-amino esters occurs rapidly, and because the A-acyl form is strongly favored under neutral or basic conditions, products arising from (mono)acylation on oxygen rather than nitrogen are not observed. 

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