SYNTHESIS OF PURE ENANTIOMERS OF CIS-3-(TRIFLUOROMETHYL) AND TRANS-3-(TRIFLUOROMETHYL) PYROGLUTAMIC ESTERS

The addition of the racemic Schiff base ethyl N-(diphenylmethylene)gly cinate (2), from glycine ester, to ethyl-4,4,4-trifluorocrotonate give s, according to the experimental conditions, one or two Michael adduct s. Acidic hydrolysis gives the cis/trans-3-(trifluoromethyl)pyroglutam ates. The enantiomerically pure Schiff base, prepared from chiral 2-hy droxy-3-pinanone and t-butyl glycinate, reacts with trans-ethyl-4,4,4- trifluorocrotonate to produce four diastereoisomers which may be separ ated and hydrolysed to give enantiomerically pure cis- and trans-3-(tr ifluoromethyl)pyroglutamate.