Featured Article: Asymmetric Transfer Hydrogenation
Track the Conversion of Alkynyl Ketones to Propargyl Alcohols
The authors report the use of a chiral spiro iridium catalyst for the asymmetric transfer hydrogenation of various alkynyl ketones to chiral propargyl alcohols with high yield and enantioselectivity. They found that when using HCO2Na as the hydrogen donor, the alkynyl ketone converted to propargylic alcohol with 97% e.e. To improve the speed of the hydrogenation they used HCO2Cs, since the cesium compound has higher solubility in ethanol than the equivalent sodium compound.
In situ FTIR spectroscopy was used to track the asymmetric transfer hydrogenation and provide insight into the reaction mechanism. The results show that HCO2Cs was converted to cesium ethyl carbonate (EtOCO2Cs) after providing hydrogen, and that the spectral peak for the ketone disappeared over time. Information provided by the spectra indicate that the formate salt and EtOH serve as the hydride and proton sources, respectively.
Zhang, Y-M., Yuan, M-L., Liu, W-P., Xie, J-H., Zhou, Q-L., “Iridium-Catalyzed Asymmetric Transfer Hydrogenation of Alkynyl Ketones Using Sodium Formate and Ethanol as Hydrogen Sources”, Org. Lett. 2018, 20, 4486−4489. DOI:10.1021/acs.orglett.8b01787