1,4-Additions of PhCu · BF₃, n-Bu · BF₃ and MeCu · BF₃ to the trans-8-phenyl-menthyl enoates 1 proceeded with high chiral induction. Saponification of the resulting esters 2 gave the corresponding enantiomerically pure β-substituted alkanoic acids 3 and the recovered (−)-8-phenylmenthol in good overall yields. Analogous additions to the cis-crotonate 1 led preferentially to the acids 3 enantiomeric to those obtained from the trans-crotonate 1, although with lower selectivity. A stereochemical model is proposed consistent with the observed results (Scheme 2, Table).