Brine-Stabilized 2,2,2-Trifluorodiazoethane and Its Application in the Synthesis of CF₃–Substituted Cyclopropane α‑Amino Acids

A facile thermodynamic cyclopropanation of trisubstituted olefinic azlactones with a stock solution of CF3CHN2 in CH3CN is realized. This method shows excellent generality, affording a wide range of trifluoromethyl-substituted cyclopropanes bearing azlactone rings in good to high yields and diastereoselectivities. With the products in hand, the trifluoromethyl-substituted cyclopropane α-amino acids and relative peptide derivatives could be readily obtained.