Enantioselective Hydrogenation on Cinchona-Modified Metal Catalysts:Mechanistic Implications of Acid Additive
نویسندگان
چکیده
The enantioselective hydrogenation of 4-hydroxy-6-methyl-2pyrone in the presence of acetic acid and trifluoroacetic acid has been studied on cinchonidine-modified Pd/TiO2. Catalytic experiments and theoretical calculations indicate the formation of a cinchonidine–trifluoroacetic acid cyclic ion pair. We propose that this is the actual modifier, which interacts with 4-hydroxy-6-methyl2-pyrone in the enantiodifferentiating step. The new mechanistic model is assumed to be valid also for other reactions over cinchona-modified Pt or Pd, in the presence of trifluoroacetic acid. c © 2002 Elsevier Science
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