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Enantio- and anti-Diastereoselective Aldol Additions of Acetates and Propionates via O-Silyl Ketene Acetals†
†
This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. We thank F. Lippert for carrying out some of the experiments, Prof. R. Baker, Southampton, for data on the optical rotation of 19, and Prof. B. Ganem, Cornell University, for a sample of ent-20. For definition of the descriptors syn and anti see [4a].
Graphical Abstract
A direct route to β-hydroxyketones 1a and 1b, which are of importance for naturl product syntheses, starts from the acetates or propionates of the alcohols 2a and 2b. The highly stereoselective aldol condensation is achieved by a Mukaiyama reaction.
−9.4 (c = 0.6 CHCl3); 19 (cf.[4c]):[α]D −7.5 (c = 1.8, CH2Cl2); 20 from 16:[α]
+ 11.3 (c = 0.6, CHCl3); ent- 20 (vgl.[11]):[α]
−10.3 (c = 0.2, CHCl3).
