A series of Mn(I) catalysts containing
imidazole-based chiral PNN tridentate ligands with controllable “side
arm” groups have been established, enabling the asymmetrical
hydrogenation of unsymmetrical benzophenones with outstanding activity
(up to 13 000 TON) and excellent enantioselectivity (up to
>99% ee). This protocol uses K2CO3 as an industrially desirable base and features a wide substrate
scope and functional group tolerance. Moreover, the imine group in
the catalyst is crucial for accessing high activities and good enantioselectivities.
The asymmetric Pictet-Spengler reaction between tryptamine derivatives and aldehydes has been developed with a cinchona alkaloid squaramide as the catalyst, affording the corresponding tetrahedron-β-carbolines in good to excellent yields and ee values. A rational mechanistic pathway has also been proposed based on DFT calculations.
A series of Mn(I) catalysts containing imidazole-based chiral PNN tridentate ligands with controllable ‘side arm’ groups have been established, enabling the inexpensive base-promoted asymmetric hydrogenation of simple ketones with outstanding activities (up to 8200 TON) and good enantioselectivities (up to 88.5% ee). This protocol features wide substrate scope and functional group tolerance, thereby providing easy access to a key intermediate of crizotinib.
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