Inversion of Enantioselectivity in Allene Gas versus Allyl Acetate Reductive Aldehyde Allylation Guided by Metal-Centered Stereogenicity: An Experimental and Computational Study

The use of gaseous allene as an allyl
pronucleophile in enantioselective
aldehyde reductive coupling is described. Notably, using the same
antipode of chiral ligand, (S)-tol-BINAP, an inversion
of enantioselectivity is observed for allene versus allyl acetate
pronucleophiles. Experimental and computational studies corroborate
intervention of diastereomeric π-allyliridium-C,O-benzoate complexes,
which arise via allene hydrometalation (from a pentacoordinate iridium
hydride) versus allyl acetate ionization (from a square planar iridium
species).