Development of spirocyclic phosphoramidite-based hybrid diphosphorus ligands for enantioselective iridium-catalyzed hydrogenation of imines.

Unsymmetrical hybrid chiral diphosphorus ligands bearing a spirocyclic phosphoramidite scaffold have been developed and successfully applied in the iridium-catalyzed asymmetric hydrogenation of imines. With this newly developed chiral iridium catalytic system, a wide range of imines including sterically hindered ones could be hydrogenated to give the corresponding optically active amines in high yields (up to >99%) and with excellent enantioselectivities (up to >99% ee). The utility of this hydrogenation has been demonstrated by the preparation of the chiral fungicide (S)-benalaxyl.

Intramolecular Copper-Catalyzed Asymmetric Propargylic [4 + 2]- Cycloaddition toward Optically Active Tetrahydroisoindolo[2,1-a]quinoxalines.

An intramolecular Cu-catalyzed asymmetric propargylic [4 + 2] cycloaddition of bis-N-nucleophile-functionalized propargylic esters has been realized in the support of a chiral tridentate N-ligand, (S,S)-Pybox-diOAc, leading to chiral tetrahydroisoindolo[2,1-a]quinoxalines in high yields and with good to excellent enantioselectivities. The reaction features high efficiency, simplicity, and broad substrate scope, thus providing a powerful and concise strategy for stereoselective access to optically active polycyclic heterocycle frameworks that are otherwise difficult to synthesize.