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 trams-4-hydroxy-L-proline through oxidation of fluorinated prolinates with RuO4.