Novel Ir-SYNPHOS^® and Ir-DIFLUORPHOS^® Catalysts for Asymmetric Hydrogenation of Quinolines

Abstract

Novel Ir-SYNPHOS and Ir-DIFLUORPHOS catalysts were synthesized and used for the synthesis of tetrahydroquinolines via asymmetric hydrogenation of the corresponding quinoline ­derivatives.

Key words

catalysts - iridium - hydrogenation - enantioselectivity

References and Notes

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15

General Hydrogenation Procedure
The Ir complex (0.01 mmol) was placed in a dry 10 mL Schlenk tube which was equipped with a magnetic bar, a stopper, and connected to a supply of vacuum/argon. Degassed anhydrous acetone (2 mL) was introduced via a syringe under a stream of argon. The mixture was degassed with three vacuum/argon cycles. Methanolic HBr (2.2 equiv) was added dropwise to the solution and stirred for 30 min at r.t. The precipitate was concentrated under vacuum and anhydrous THF (2 mL) was introduced via syringe under a stream of argon. Then, the solution was degassed again with three vacuum/argon cycles. The mixture was transferred by a syringe to a dry 10 mL Schlenk tube, in which I₂ (0.1 mmol) and quinoline (1 mmol) were placed beforehand. This Schlenk tube was equipped with a magnetic bar, a stopper, and connected to a supply of vacuum/argon. The mixture was degassed with three vacuum/argon cycles. The hydrogenation was performed under H₂ (50 bar) at 30 °C for 24 h. After releasing the hydrogen, the reaction mixture was concentrated and the crude product was purified by a short silica gel column eluted with cyclohexane-EtOAc.