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Achiral CpxIr(III)/Chiral Carboxylic Acid Catalyzed Enantioselective C–H Amidation of Ferrocenes under Mild Conditions

Ir­(III)-catalyzed
enantioselective C–H activation generally
relies on the combination of chiral Ir­(III) cyclopentadienyl complexes
with chiral carboxylic acids to ensure high enantiocontrol. We report
herein the achiral CpxIr­(III)-catalyzed enantioselective
C–H amidation of ferrocenes. Crucial to the high enantioselectivity
is the use of a chiral carboxylic acid ligand derived from tert-leucine via Pd­(II)-catalyzed γ-C­(sp3)–H arylation and a sterically more hindered CpxIr­(III) catalyst. This reaction proceeds smoothly under very mild
conditions (0 °C) and tolerates a wide range of ferrocene carboxamides
and dioxazolones, providing the amidation products in good yields
with high enantioselectivity (up to 97.5:2.5 er). This protocol might
open the way for achiral CpxIr­(III)-catalyzed asymmetric
C–H activation.