Application of Ferrocenylalkyl Chiral Auxiliaries to Syntheses of Indolenine Alkaloids: Enantioselective Syntheses of Vincadifformine, ψ- and 20-epi-ψ-Vincadifformines, Tabersonine, Ibophyllidine, and Mossambine

Abstract

Condensations of the chiral N-ferrocenylethylindoloazepines 4a,b, with the aldehydes 5, 13, 19, 29, and 32, led to tetracyclic vinylogous urethanes 6a,b and 7, 14a and 14b, 21a,c and 21b,d, 30a and 31a, and 30b and 31b. Respectively, 6:1, 5:1, 3:1, 1.7:1, and 2:1 diastereomeric selections provided intermediates which, on cleavage of the chiral auxiliary N-substituent and subsequent elaboration of ring D of the Aspidosperma and Strychnos alkaloids, provided enantiomerically pure (−)-ψ- and (−)-epi-ψ-vincadifformines (1, 2), (+)-ibophyllidine (12), (+)- and (−)-vincadifformine (16a, 16b), (−)-tabersonine (27), and (−)-mossambine (41).