Enantioselective (up to 87% ee) epoxidation of a variety of α,β-enones to form α,β-epoxy ketones is described using a series of fluorous α,α-diaryl-l-prolinols as bifuncational organocatalysts and tert-butyl hydrogenperoxide (TBHP) as an oxidant.
An operationally simple and recoverable fluorous CBS methodology was developed. The in situ-generated fluorous oxazaborolidine efficiently catalyzed the reduction of ketones with high enantioselectivity and reactivity. The subsequent recycling of the fluorous prolinol precatalyst was achieved by fluorous solid-phase extraction.
CBS Reductions with a Fluorous Prolinol Immobilized in a Hydrofluoroether Solvent
作者:Qianli Chu、Marvin S. Yu、Dennis P. Curran
DOI:10.1021/ol702778v
日期:2008.3.1
A fluorous prolinol precatalyst bearing only 34 fluorine atoms has been immobilized in the hydrofluoroether solvent HFE-7500. The,CBS reduction of acetophenone proceeded rapidly, in high yield and in high ee in the absence of any organic solvent. The organic product was stripped from the HFE-7500 phase with a polar solvent, and the HFE-7500 phase was reused "as is" with satisfactory results through eight runs. This process is an attractive prototype for the large-scale use, recovery, and reuse of fluorous organocatalysts.