The influence of solvent on the Yb(OTf)3 or BF3·Et2O-catalyzed reaction of (trifluoromethyl)aldimines with ethyl diazoacetate has been investigated. The reaction of fluoral ethyl hemiacetal, an aromatic amine, and ethyl diazoacetate could be performed in 1,1,1,3,3,3-hexafluoropropan-2-ol to provide the corresponding (trifluoromethyl)aziridines.