New Synthesis and Chirality of (−)-4,4,4,4′,4′,4′-Hexafluorovaline

(?)-(R)-4,4,4,4′,4′,4′-Hexafluorovaline hydrochloride ((R)- 5 ) of 98% ee is prepared from β,β-bis(trifluoromethyl)acrylic acid (= benzyl 4,4,4-trifluoro-3-(trifluoromethyl)but-2-enoate; 1 ) in 4 steps with an overall yield of 9.6%. Key step is the separation of the TsOH salts of the diastereoisomers obtained by anti-Michael addition of (+)-(R)-1-phenylethylamine ( 2 ) to 1 (→ (R,R)- 3 ). In contrast to the published (S)-chirality, the X-ray structure analysis of (R,S)- 6 reveals, that (R)-chirality has to be assigned to the levorotatory (?)-4,4,4,4′,4′,4′-hexafluorovaline hydrochloride.