An Improved Catalyst for the Asymmetric Arylation of Ketone Enolates
“An Improved Catalyst for the Asymmetric Arylation of Ketone Enolates”, J. Am. Chem. Soc., 2002, 124(7), 1261-1268.
A new catalyst system for the enantioselective alpha-arylation of ketones is reported. This catalyst, prepared from Pd-2(dba)(3) and a bulky dialkylphosphino-binaphthyl ligand, is able to effect the asymmetric arylation of ketone enolates with aryl bromides utilizing (NaOBu)-Bu-t as base. These new catalysts enjoy much higher reactivity than previous systems; arylation reactions could be effected at room temperature with only 2 mol % of the Pd catalyst. The coupling of alpha-alkyl-alpha'-protected cyclopentanones proceeded in high yield, and the resulting quaternary stereogenic center was installed in up to 94% ee.