1

Chiral Anion-Mediated Asymmetric Ion Pairing Chemistry

Reporter: Zhi-Yong Han2010-12-31

Background and Introduction

Ion Pair ( by Bjerrum in 1926)A pair of oppositely charged ions held together by Coulomb attraction without formation of a covalent bond.

contact (tight or intimate)ion pair

solvent separated ion pair solvent-shared ion pair

“Strict” electrostaticion pair

H-bonded charge-assistedsupramolecular entity

Ion Pairing Chemistry

Brønsted acidcatalysis

Structure and properties of anionic counterions

Chiral Anions

Carboxylate and sulfonate anions Borate anions

phosphate anionsHexacoordinated phosphorus anions

Other anionic structures

Carboxylate and sulfonate anions

Application: enantiomeric resolutions

Water-soluble sulfonated resorcarenescommercially availablecyclic polyacids

Borate anions

Mariappan Periasamy, J. Org. Chem. 1999, 64, 7643-7645

Precipitate

Filtrate

dil HCl

dil HCl

(S)-BINOL29%, ee>99%

(R)-BINOL53%, ee=56%

Up to 34% ee

B. A. Arndtsen, Org. Lett., 2000, 2, 4165–4168.

Borate anions

1.Ag2CO3

2.CuCl

Borate anions

ee < 26%

Bruce A. Arndtsen Organometallics 2004, 23, 2838-2840

Borate anions

A. Nelson, Tetrahedron: Asymmetry, 2003, 14, 1995–2004.

A+ : Ag, Na, Et2NH2 +, Et3NH +

Borate anions

Up to 84% ee

Walter Leitner Angew. Chem. Int. Ed. 2006, 45, 3689 –3692

Borate anions

+

(R)-BLA 1

-78 °C.

99% yield99% ee

Hisashi Yamamoto J. Am. Chem. Soc. 1998, 120, 6920-6930

Borate anions

Gary B. Schuster J. Am. Chem. Soc. 1998, 120, 1705-1717

B. List, Angew. Chem., Int. Ed., 2006, 45, 4193–4195

B. List, Angew. Chem., Int. Ed., 2008, 47, 1119–1122.

F. D. Toste, Science, 2007, 317, 496–499.

E. N. Jacobsen, J. Am. Chem. Soc., 2007, 129, 13404–13405.

E. N. Jacobsen, J. Am. Chem. Soc., 2008, 130, 7198–7199.

VAPOL-Boron Lewis Acid?

Up to 98% ee

Jon C. Antilla and William D. Wulff*J. Am. Chem. Soc. 1999, 121, 5099-5100

Catalyst structure not determined

Wulff, W. D. Eur. J. Org. Chem. 2007, 206, 8–2071.

VAPOL-Boron Lewis Acid?

Scope and Mechanistic Studies

Wulff, W. D. Chem.sEur. J. 2008, 14, 3785–3803.

Catalyst structure determination

No non-linear effect.The results suggest that it is likely that only one molecule of the ligand is involved in theactive catalyst.

Wulff, W. D. Chem.sEur. J. 2008, 14, 3785–3803.

Catalyst structure determination

Wulff, W. D. Chem.sEur. J. 2008, 14, 3785–3803.

Evidence: Boroxinate Based Brønsted Acid

William D. WulffJ. AM. CHEM. SOC. 2009, 131, 15615–15617

To form catalyst 10, >3 fold of borane was needed