New asymmetric routes to ajmaline and suaveoline indole alkaloids

The tetracyclic advanced intermediates 6,8 and 9 obtained from L-tryptophan via a cis-selective Pictet-Spengler reaction and a Dieckmann-Thorpe cyclisation are used in a range of new approaches to polycyclic monoterpenoid indole alkaloids such as ajmaline and suaveoline. Structural modifications designed to facilitate a key intermolecular addition to C15 (ajmaline numbering) are described, followed by two intramolecular routes based on the addition of a suitable carbon fragment to a remote nitrogen atom prior to bond formation at C15. © The Royal Society of Chemistry 2000.