Preparation of Chiral Homoannularly Bridged N,P‐Ferrocenyl Ligands by Intramolecular Coupling of 1,5‐Dilithioferrocenes and Their Application in Asymmetric Allylic Substitution Reactions

Abstract

AbstractHomoannularly bridged ferrocene 6b was prepared by intramolecular coupling of 1,5‐dilithioferrocene 5b mediated by Fe(acac)3. Dilithioferrocene 5b was prepared by lithium–halogen exchange of the corresponding diiodide, which was prepared by 1,5‐dilithiation of the o‐TMS‐blocked ferrocene and followed by trapping with iodine and removal of the TMS group. Alternatively, 5b could be readily prepared by the reaction of o‐bromophenylferrocene 8 with nBuLi (>2 equiv.). The benzene ring of 6b underwent ortho lithiation with tBuLi, and the resulting lithiated species was trapped with Ph2PCl to produce corresponding aminophosphane 7d. Aminophosphane 13, which has the phosphanyl group on the cyclopentadienyl ring, was prepared by intramolecular coupling of 1,5‐dilithiated PhPPFA 11 mediated by Fe(acac)3. New N,P ligands 7d and 13 were used in the palladium‐catalyzed allylic alkylation and amination of 1,3‐diphenyl‐2‐propenyl acetate (14), and ligand 7d was found to give good yields with enantioselectivities as high as 96 % ee. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)