Organocatalytic Transfer Hydrogenation of Cyclic Enones
The first enantioselective organocatalytic transfer hydrogenation of cyclic enones has been accomplished. The use of iminium catalysis has provided a new organocatalytic strategy for the enantioselective reduction of β,β-substituted α,β-unsaturated cycloalkenones, to generate β-stereogenic cyclic ketones. The use of imidazolidinone 4 as the asymmetric catalyst has been found to mediate the hydrogenation of a large class of enone substrates with tert-butyl Hantzsch ester serving as an inexpensive source of hydrogen. The capacity of catalyst 4 to enable enantioselective transfer hydrogenation of cycloalkenones has been extended to five-, six-, and seven-membered ring systems. The sense of asymmetric induction is in complete accord with the stereochemical model first reported in conjunction with the use of catalyst 4 for enantioselective ketone Diels−Alder reactions.
Additional Information© 2006 American Chemical Society. Received July 24, 2006. Publication Date (Web): September 8, 2006. Financial support was provided by the NIHGMS (R01 GM66142-01) and kind gifts from Amgen, Merck, and the Astellas Foundation. S.G.O. is grateful for an NSERC fellowship.
Supplemental Material - ja0653066si20060829_010015.pdf