Short communicationHighly enantioselective reduction of ketones in air catalyzed by Rh-based macrocycles

Add time:10/01/2019    Source:sciencedirect.com

The asymmetric transfer hydrogenation (ATH) of ketones catalyzed by Rh-based macrocycles proceeded smoothly in the presence of air with high catalytic activity and enantioselectivity. Even though the S/C ratio (substrate to catalyst molar ratio) was increased up to 2000:1, the ATH of ketone still afforded 92% isolated yield with 92% ee. Notably, the Rh-based macrocycles could be successfully used to catalyze the ATH of ketones without any need of inert atmosphere, which further highlighted its advantage over those generally air-sensitive transition metal catalysts. The addition of NH4I greatly improved both the catalytic activity and enantioselectivity. On the basis of NMR evidence, we postulate that the NH4I significantly enhanced the coordination between chiral macrocyclic ligands and rhodium center.

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