Kinetic Resolution of β‐Alkenyl‐, β‐Alkynyl‐ and β‐Flavenyl‐Substituted β‐Hydroxy Esters in Asymmetric Dehydration

Catalytic asymmetric dehydration of β-alkenyl- or alkynyl-substituted β-hydroxy esters by kinetic resolution has been investigated with five different chiral ligands 3–7. The kinetic resolution of a variety of racemic β-hydroxy tert-butyl esters in the presence of a prolinol chiral ligand and BrZnCH2CO2tBu provided highly enantio-enriched β-hydroxy esters 9–22 with selectivity factors ranging from 11 to 59. In addition, the application of this asymmetric synthetic methodology to the preparation of enantio-enriched flavene derivatives 23–29 is demonstrated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)