Trifluoromethylated azomethine ylide 1, generated in situ by the conrotatory ring opening of cis-2-benzoyl-1-methyl-3-trifluoromethylaziridine, cycloadded with both electron-deficient and -rich monosubstituted olefins to give exclusively the corresponding 3-substituted pyrrolidines. This high regioselectivity is discussed in connection with the interaction between 1-LUMO and olefin-HOMO.