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