Ergiebige Herstellung von ( R )‐ und ( S )‐3,3,3–Trifluormilchsäure und von ( R )‐ und ( S )‐(Trifluormethyl)oxiran

Simple Access to ( R )‐ and ( S )‐3,3,3–Trifluorolactic Acid and to ( R )‐ and ( S )‐(Trifluoromethyl)oxirane Ethyl trifluoropyruvate (from hexafluoropropylene oxide) is reduced by NaBH 4 to rac ‐trifluorolactic acid which is resolved on a 100–g scale by salt formation with ( R,R )‐ and ( S,S )‐2–amino–1‐phenyl–1,3–propanediol (readily available intermediates of industrial chloroamphenicol synthesis). The enantiomerically pure trifluorolactic acids (>99% ee by GC analysis on cyclodextrin columns) are converted into ( R )‐ and ( S )‐(trifluoromethyl)oxirane in an overall yield of 73% by the following steps: esterification, THP protection of the OH group, LAH reduction and mesylation to the 2–THP–protected mesylate of 3,3,3–trifluoro–1,2–propanediol, and one–pot deprotection (Dowex 50) and cyclization (NaOCH 2 CH 2 OH) in ethylene glycol. The enantiomeric purity of the oxirane (b.p. 39C, isolated on a 10–g scale) was determined by GC to be >99%. Possible synthetic targets are mentioned which should be accessible in enantiomerically pure form from the (trifluoromethyl)oxirane described here.