Versatile stereocontrol in kinetic resolution of a diphenylphosphinyl-protected α-amino aldehyde by reaction with chiral phosphonates |
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Authors: | Reinhard Kreuder Tobias Rein Oliver Reiser |
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Institution: | aInstitut für Organische Chemie der Georg-August-Universität, Tammanstr. 2, D-37077 Göttingen, Germany;bDepartment of Organic Chemistry, Technical University of Denmark, DK-2800 Lyngby, Denmark;cInstitut für Organische Chemie der Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany |
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Abstract: | In kinetic resolutions of the racemic aldehyde 1 by reaction with chiral phosphonates of type 2, all of which contain the same chiral auxiliary in the same enantiomeric form, any of the four diastereomers 3a, 3b, 4a or 4b can be obtained as the main product by an appropriate choice of reaction parameters (geometric selectivities from 66:34 to 98:2, diastereomer ratios between 93:7 and ≥99:1). The switch in stereoselectivity observed when KHMDS or NaHMDS is used as base instead of KHMDS/18-crown-6 is rationalized as resulting from a change in influence of the aldehyde α-stereocenter from Felkin-Anh-Eisenstein to chelation control. |
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