Copper(I)-Catalyzed Asymmetric 1,4-Conjugate Hydrophosphination of α,β-Unsaturated Amides

A catalytic asymmetric conjugate
hydrophosphination of α,β-unsaturated amides is accomplished
by virtue of the strong nucleophilicity of copper­(I)-PPh2 species, which provides an array of chiral phosphines bearing an
amide moiety in high to excellent yields with excellent enantioselectivity.
Furthermore, the dynamic kinetic resolution of unsymmetrical diarylphosphines
(HPAr1Ar2) is successfully carried out through
the copper­(I)-catalyzed conjugate addition to α,β-unsaturated
amides, which affords P-chiral phosphines with good-to-high
diastereoselectivity and high enantioselectivity. 1H NMR
studies show that the precoordination of HPPh2 to copper­(I)-bisphosphine
complex is critical for the efficient deprotonation by Barton’s
Base. Moreover, the relative stability of the copper­(I)-(R,RP)-TANIAPHOS complex
in the presence of excessive HPPh2, confirmed by 31P NMR studies, is pivotal for the high asymmetric induction, as the
ligand exchange between bisphosphine and HPPh2 would significantly
reduce the enantioselectivity. At last, a double catalytic asymmetric
conjugate hydrophosphination furnishes the corresponding product in
high yield with high diastereoselectivity and excellent enantioselectivity,
which is transformed to a chiral pincer palladium complex in moderate
yield. This chiral palladium complex is demonstrated as an excellent
catalyst in the asymmetric conjugate hydrophosphination of chalcone.