10.1002/chem.201604995
Chemistry - A European Journal
COMMUNICATION
increases the nucleophilicity of intermediate I by preventing ion-
pairing of the anionic nitrogen atom with the Pd(II).[6a] In a simul-
taneous separate cycle, an iminium-ion intermediate II is formed
from the condensation of an -unsaturated aldehyde 2 with the
aminocatalyst 3. Then, reversible aza-Michael addition of the in-
situ generated intermediate I to intermediate II results in a rapid
epimerization of diastereomeric intermediates IIIa, IIIb under the
reaction conditions. Next, diastereomer IIIa preferentially under-
goes a fast irreversible intramolecular cyclization which takes
place on the Si-face of the chiral enamine. Subsequently, hy-
drolysis of iminium-ion intermediate IV, and concomitant decom-
plexation of the Pd(0) allow regeneration of both catalysts, thus
completing the synergistic catalytic cycle. Overall, the asymmet-
ric reaction can be considered as an asymmetric formal [3+2]
cycloaddition, which is likely to proceed in a stepwise manner
through a DYKAT type IV, generating the chiral pyrrolidine 4.
Thanks are expressed to reviewers for suggestions for experi-
ments.
Keywords: Synergistic Catalysis • Vinyl Aziridines • Organoca-
talysis • Transition Metal Catalysis
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Acknowledgements
Thanks are expressed to Aarhus University, Carlsberg Founda-
tion and FNU for financial support. F.T. acknowledges the Euro-
pean Commission for a Marie Curie Intra European Fellowship
for Career Development (PIEF-GA-2013-622413). Vibeke H.
Lauridsen is acknowledged for assistance with X-ray analysis.
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