Application of ferrocenylalkyl chiral auxiliaries to syntheses of indolenine alkaloids:: Enantioselective syntheses of vincadifformine, ψ- and 20-epi-ψ-vincadifformines, tabersonine, ibophyllidine, and mossambine

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 (-)-psi- and (-)-epi-psi-vincadifformines (1, 2), (+)-ibophyllidine (12), (+)-and (-)-vincadifformine (16a, 16b), (-)-tabersonine (27), and (-)-mossambine (41).