Synthesis of Diastereomeric Bis(oxazoline) Ligands Derived from (S,S)-1,1′-Bis(4-isopropyloxazolin-2-yl)ferrocene

Abstract

Starting from (S,S)-1,1′-bis(4-isopropyloxazolin-2-yl)ferrocene, all possible 2-trimethylsilyl- and 2,2′-di(trimethylsilyl)-substituted diastereoisomers, potential bisoxazoline ligands for use in asymmetric catalysis, were synthesised by selective lithiation followed by addition of trimethylsilyl chloride. Access to the (S,S,R p,R p)-diastereoisomer was achieved following diastereoselective introduction of two deuterium-blocking groups and utilisation of the high k H/k D value for lithiation, methodology that was also applied to the synthesis of a related 2,2′-di(diphenylmethanol)bisoxazoline ligand.