Enantioselective reductions of [m] ferrocenophanones

Enantioselective reductions of prochiral ferrocenophane ketones were investigated. Oxazaborolidine mediated reduction led to corresponding chiral alcohols generally in good yields and enantioselectivities up to 97% ee. Ruthenium-catalyzed transfer hydrogenation was rather unsuccessful in reducing cyclic ferrocene ketones. Proline-derived activator together with trichlorosilane also proved to be an effective method for some substrates (up to 99% ee). Pronounced tendency of α-ferrocenyl ketones toward reductive deoxygenation was studied by DFT computational methods.

Graphical abstractProchiral ferrocenophane ketones were enantioselectively reduced. Oxazaborolidine mediated reduction and proline-derived activator with trichlorosilane proved to efficient methods, with enantioselectivities up to 97% ee and 99% ee, respectively. Ruthenium-catalyzed transfer hydrogenation was rather unsuccessful in reducing cyclic ferrocene ketones.Figure optionsDownload full-size imageDownload as PowerPoint slide