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Short Paper | Regular issue | Vol 100, No. 9, 2020, pp.1441-1449
Published online, 14th July, 2020
DOI: 10.3987/COM-20-14284
■ Improved Synthesis of Cyclohexane-Backbone Iridium-Complexes of Quinoline-Phosphine and Their Applications in Asymmetric Hydrogenation

Qibin Liu*

*R&D department, Dalian Allychem Co. Ltd, No 5 of Jinbin Road, Jinzhou New District 116620, China

Abstract

The iridium-complexes 3 and 4 with cyclohexane-backbone derived from quinoline were easily synthesized. The key step is cis/trans stereoselective reduction of 2-(quinolin-2-yl)cyclohexanone 5 to trans-2-(quinolin-2-yl)cyclohexanol 6 using Al(Oi-Pr)3/i-PrOH and the following diastereomeric optical resolution of racemic 6 using 0.50 equiv (S)-mandelic acid in EtOAc. These complexes were used in the asymmetric hydrogenation of (E)-1,2-diphenylpropene with up to 13% ee/48% conv. using 3 and 35% ee/9% conv. using 4. For the hydrogenation of (2H-chromen-3-yl)methanol, up to 80% ee/95% yield and 72% ee/96% yield were achieved. The same configuration of the products by using 3 and 4 suggested that the absolute configuration was controlled by the configuration of the stereogenic quinolinyl-bearing carbon of the complexes.