Synlett 2006(5): 0766-0770  
DOI: 10.1055/s-2006-933107
LETTER
© Georg Thieme Verlag Stuttgart · New York

Ligand Tailoring: The First Modular Assembly of Atropisomeric Biarylbisphosphine Ligands

Frédéric Leroux*a, Hanspeter Mettlerb
a Laboratoire de Stéréochimie (UMR CNRS 7509), Université Louis Pasteur (ECPM), 67087 Strasbourg Cedex 2, France
Fax: +33(3)90242742; e-Mail: lerouxf@ecpm.u-strasbg.fr;
b LONZA AG, 3930 Visp, Switzerland
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Publication History

Received 19 October 2005
Publication Date:
09 March 2006 (online)

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Abstract

Strategies based on highly selective halogen-metal permutations have been devised and applied enabling the modular assembly of atropisomeric biaryl bisphosphines. After resolution on chiral column, the ligands were tested in benchmark hydrogenation reactions affording good to excellent enantioselectivity.

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Representative Procedure for the Selective Bromine-Lithium Exchange.
n-BuLi (0.10 mol) in hexanes (63 mL) was added at -75 °C to a solution of 2,2′,6,6′-tetrabromo-1,1′-biphenyl (47 g, 0.10 mol) in THF (500 mL). The mixture was consecutively treated with fluorodimethoxyborane diethyl ether (19 mL, 16 g, 0.10 mol), a 3.0 M aq solution of NaOH (36 mL) and 30% aq H2O2 (10 mL, 3.6 g, 0.10 mol). The reaction mixture was neutralized at 25 °C with 2.0 M HCl (100 mL) and extracted with Et2O (3 × 100 mL). The combined organic layers were washed with a 10% aq solution of Na2SO3 (100 mL), dried over Na2SO4 and evaporated. The oily residue was dissolved in DMSO (200 mL) before MeI (7.5 mL, 17 g, 0.12 mol) and KOH powder (6.7 g, 0.12 mol) were consecutively added. After 1 h, H2O (500 mL) was added and the product was extracted with Et2O (3 × 100 mL). The organic layers were dried over Na2SO4 and evaporated. Crystallization from EtOH (100 mL) afforded 35 g (82%) product as colorless cubes; mp 184-185 °C. 1H NMR (400 MHz, CDCl3): δ = 7.64 (d, J = 8.3 Hz, 2 H), 7.30 (m, 2 H), 7.11 (t, J = 8.1 Hz, 1 H), 6.96 (dd, J = 7.2, 2.2 Hz, 1 H), 3.77 (s, 3 H). 13C NMR (101 MHz, CDCl3): δ = 157.6, 139.5, 131.5, 130.5, 130.2, 125.1, 124.6, 124.3, 110.0, 56.3. Anal. Calcd (%) for C13H9Br3O (420.92): C, 37.09; H, 2.16. Found: C, 37.10; H 2.03.