Mechanistic investigation of the 2,5-diphenylpyrrolidine-catalyzed enantioselective alpha-chlorination of aldehydes |
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| Authors: | Halland Nis Alstrup Lie Mette Kjaersgaard Anne Marigo Mauro Schiøtt Birgit Jørgensen Karl Anker |
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| Affiliation: | Danish National Research Foundation, Center for Catalysis, Department of Chemistry, Aarhus University, 8000 Aarhus C, Denmark. |
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| Abstract: | The mechanism for the 2,5-diphenylpyrrolidine-catalyzed enantioselective alpha-chlorination of aldehydes with electrophilic halogenation reagents has been investigated by using experimental and computational methods. These studies have led us to propose a mechanism for the reaction that proceeds through an initial N-chlorination of the chiral catalyst-substrate complex, followed by a 1,3-sigmatropic shift of the chlorine atom to the enamine carbon atom. The suggested reaction course is different from previously proposed mechanisms for organocatalytic enamine reactions, in which the carbon-electrophile bond is formed directly. Furthermore, the rate-determining step in the overall reaction was determined and the presence of nonlinear effects was probed. |
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| Keywords: | asymmetric catalysis chlorination density functional calculations isotope effects kinetics sigmatropic rearrangement |
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