Synthesis of Chiral Pyridylphenols for the Enantioselective Addition of Diethylzinc to Aldehydes

Chiral 8-substituted 2-(8,10,10-trimethy1-6-aza-tricyclo[7.1.1.0(2,7)]undeca-2(7),3,5-trien-5-yl)-phenols were prepared from a high enantiopurity (>97% ee) of (1R)-(+)-alpha-pinene, and assessed in the enantioselective addition of diethylzinc to substituted benzaldehydes, giving the (S)-alcohols with enantiomeric excess ranging from 33% to 89%. Interestingly, in all cases, except for those of ortho-chlorobenzaldehyde, ortho- and para-methoxybenzaldehydes, the ee was >71%. The plot of the Hammett substitution constants vs. enantiomeric excess of the diethylzinc addition to either the ortho- or para-substituted benzaldehydes shows a linear correlation.