Acetyl-BINOL as mimic for chiral beta-diketonates: a building block for new modular ligands

作者：von Roenn Robert; Christoffers Jens^*

来源：Tetrahedron, 2011, 67(2): 334-338.

DOI：10.1016/j.tet.2010.11.037

• Homogeneous catalysis
• Chiral ligands
• BINOL derivatives
• Asymmetric catalysis
• Titanium
• Amino acid derivatives

alpha-Acetyl-(S)-BINOL was prepared by ortho-lithiation and subsequent acetylation of acetal-protected (S)-BINOL. The beta-hydroxyketone moiety of this compound is herein a structural mimic for a beta-diketonate and forms six-membered chelates with transition metal ions. The second hydroxy-function was submitted to esterification with several carboxylic acids bearing another donor function, thus, new tridentate chiral ligands were obtained. Out of this library the L-proline-alpha-acetyl-(S)-BINOL-ester was identified to be most effective for the titanium-mediated addition of Et(2)Zn to PhCHO yielding the respective secondary alcohol with up to 93% ee, which is better than with using (S)-BINOL itself. Besides a solvent dependency (use of MeCN is optimal), the proper choice of the counter-ion is crucial: anion exchange of bromide by trifluoroacetate gave a significant increase of enantioselectivity.

• 出版日期2011-1-14