High Asymmetric Induction in Conjugate Additions of RCu · BF 3 to Chiral Enoates. Preliminary communication

1,4‐Additions of PhCu · BF 3 , n ‐Bu · BF 3 and MeCu · BF 3 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) .