New ferrocenyl chiral auxiliary substituents for amines. applications to syntheses of mossambine and vinblastine

(+)-(R)-1,2-(alpha-(R)-Mesyloxy-beta -dimethyltetramethylene)-ferrocene was synthesized and used as a chiral auxiliary for N-alkylation of methyl 1,2, 3,4,5,6-hexahydroazepino [4,5-b] indole-5-xi -carboxylates. Condensation wi th aldehydes then provided tetracyclic products in a diastereomeric ratio o f at least 97:3. Gentle cleavage in acetic acid removed the chiral auxiliar y to give the corresponding secondary amines in >99% ee. Thus, key intermed iates leading to mossambine and vinblastine could be synthesized with high enantioselectivity. The enantioselectivity greatly exceeds that found with other chiral N-auxiliaries developed in our studies.