Asymmetric Three-Component Coupling Reaction of Alkyne, Enone, and Aldehyde Catalyzed by Chiral Phebox Ruthenium Catalysts

Catalytic
asymmetric three-component coupling reactions of terminal
alkynes, α,β-unsaturated ketones, and aldehydes were studied.
The chiral ruthenium complexes containing bis­(oxa­zolinyl)­phenyl
ligands were found to serve as efficient catalysts for a tandem reaction
based on conjugate addition of terminal alkynes to α,β-unsaturated
ketones and subsequent aldol reaction with aldehydes, giving β-hydroxyketone
derivatives containing α-propargyl groups in high yields with
moderate to good enantioselectivities. This method can produce various
functional molecules from commercially available substrates in a one-pot
procedure. The absolute configuration of the major product was determined
by X-ray analysis. The control experiments suggested that a ruthenium
enolate species generated in situ by conjugate addition could be involved
as an intermediate for the aldol coupling with an aldehyde.