Copper(I)-Catalyzed Asymmetric 1,3-Dipolar Cycloaddition of Azomethine Ylides with Fluorinated Imines: The Expanded Scope and Mechanism Insights

The mechanism of
the Cu­(I)/(S,Rp)-PPFOMe-catalyzed
1,3-dipolar cycloaddition of azomethine
ylides with fluorinated aldimines has been studied using labeling
experiments, control experiments, and linear effect experiments, which
clearly ruled out the 1,3-DC/epimerization pathways and explained
the unusal exo′-selective stereochemistry.
This protocol allows for the preparation of a series of highly functionalized
fluorinated imidazolidines in good yields with excellent stereoselectivities.
Moreover, the current methods have been successfully extended to synthesize
more challenging imidazolidines bearing a CF3-containing
quaternary stereogenic center via the endo-selective
1,3-DC of azomethine ylides with trifluorinated ketimine under identical
reaction conditions.