Homologative Trifluoromethylation of Acetals

Trifluoroethyl alpha-insertion of acetals has been developed. Aromatic, heteroaromatic, and alkenyl acetals react with in situ generated (trifluoromethyl) diazomethane in the presence of antimony(V) chloride to furnish alpha-trifluoromethyl acetals. A stereoselective version of this transformation exploiting the acetal as a chiral auxiliary is also presented.