Asymmetric tricarbonyliron complexation of cyclohexadiene directed by chiral ester and amide auxiliaries

Coupling of (+)-menthol, (+)-phenylethylamine and (-)-proline methyl ester with 4-methoxy-1-cyclohexa-2,4-dieneacetic acid gave the chiral ester 1 and amides 2 and 3, respectively, which were then isomerized into the 1,3-dienes. The diastereoselection induced by the chiral ester and amide auxiliaries during complexation with nonacarbonyliron was quite encouraging. The diastereomeric ratios of the ester- and amide-Fe(CO)(3) complexes formed were determined directly from the H-1 NMR integration of observable diastereotopic chemical shifts.