Synthesis of (-)-(1S,5R)- and (+)-(1R,5S)-trifluoroanalogues of frontalin

The synthesis of enantiomerically pure (-)-(1S,5R)-1-trifluoromethyl frontalin 7 starting from (-)-(1R)-menthyl (S)-toluene-4-sulfinate, 5- pentenylmagnesium bromide and methyl trifluoroacetate is described. The synthetic procedures to obtain the enantiomer (+)-(1R,5S)-7 are also mentioned. Absolute stereochemistry was unambiguously assigned by X-ray analysis of intermediates 3 and 5.