Enantioselective Rh(I)-Catalyzed C–H Arylation of Ferroceneformaldehydes

As an important class
of platform molecules, planar chiral ferrocene
carbonyl compounds could be transformed into various functional groups
offering facile synthesis of chiral ligands and catalysts. However,
developing efficient and straightforward methods for accessing enantiopure
planar chiral ferrocene carbonyl compounds, especially ferroceneformaldehydes,
remains highly challenging. Herein, we report a rhodium­(I)/phosphoramidite-catalyzed
enantioselective C–H bond arylation of ferroceneformaldehydes.
Readily available aryl halides such as aryl iodides, aryl bromides,
and even aryl chlorides are suitable coupling partners in this transformation,
leading to a series of planar chiral ferroceneformaldehydes in good
yields and excellent enantioselectivity (up to 83% yield and >99%
ee). The aldehyde group could be transformed into diverse functional
groups smoothly, and enantiopure Ugi’s amine and PPFA analogues
could be synthesized efficiently. The latter was found to be a highly
efficient ligand in Pd-catalyzed asymmetric allylic alkylation reactions.
Mechanistic experiments supported the formation of imine intermediates
as the key step during the reaction.