Synthesis of cis-4-Trifluoromethyl- and cis-4-Difluoromethyl-l-pyroglutamic Acids

Efforts to synthesize 4-trifluoromethyl- and 4-difluoromethyl-l-pyroglutamic acids are described. After many arduous efforts, we successfully synthesized our target molecules cis−4-trifluoromethyl-l-pyroglutamic acid 25 and cis−4-difluoromethyl-l-pyroglutamic acid 26 from trans-4-hydroxy-l-proline through oxidation of fluorinated prolinates with RuO₄.