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21.1.6.15.1.2 Variation 2: By Alkylation with Epoxides and Their Derivatives

DOI: 10.1055/sos-SD-021-00136

Li, W-R.Science of Synthesis, (200521244.

Pseudoephedrine amide enolates 252 undergo alkylation with epoxides as electrophiles (Scheme 61).[‌376‌] Stereochemical matching is crucial in reactions with monosubstituted epoxides. The pairing leads either to a 1,3-syn diastereomer or to a 1,3-anti diastereomer: the pairing that gives the 1,3-syn diastereomer is highly selective and synthetically useful. Reactions of amide 252 (R1=Me) with 1-substituted oxiranes (e.g., to give 253) or 2,2-dimethyloxirane exhibit a high diastereoselectivity, whereas the reaction with oxirane shows a poor diastereoselectivity. To improve the diastereoselectivity and efficiency of this reaction, 1-(tert-butyldimethylsiloxy)-2-iodoethane has been suggested as a replacement for oxirane.

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