Synthesis 2006(21): 3631-3638  
DOI: 10.1055/s-2006-950291
PAPER
© Georg Thieme Verlag Stuttgart · New York

A Versatile Approach to Planar Chiral Monophosphane Ligands

Susan E. Gibson*, Jacob T. Rendell, Matthew Rudd
Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
Fax: +44(207)5945804; e-Mail: s.gibson@imperial.ac.uk ;
Further Information

Publication History

Received 21 August 2006
Publication Date:
09 October 2006 (eFirst)

Abstract

The enantioselective reaction of a chiral bisamide and an electrophile with benzyl ether complexes of arene tricarbonyl chromium(0) was used to introduce the asymmetry into a synthesis of novel enantiopure planar chiral ligands. Elaboration of the resulting ether complexes [η6-4-t-BuC6H4CHE1(OR)]Cr(CO)3 via a diastereo­selective ortholithiation/chlorophosphane quench protocol led to the synthesis of planar chiral monophosphane complexes with high enantiomeric purity (typically 96-98% ee) for assessment in the palladium-catalyzed asymmetric hydrosilylation of styrene. The identity of benzylic substituent E1 (installed using the chiral base reaction) was found to have a significant effect on the enantioselectivity of resulting catalysts. Removal of the tricarbonylchromium(0) unit from the structurally optimized phosphane ligand was accomplished using a high-yielding borane protection-aerial oxidation-deprotection strategy.

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All HPLC analyses were carried out with racemic samples created using t-BuLi instead of the diamide of (+)-3.