Pd. Bailey et al., NEW ASYMMETRIC ROUTE TO BRIDGED INDOLE ALKALOIDS - FORMAL SYNTHESES OF (-)-SUAVEOLINE, (-)-RAUMACLINE AND (-)-N-B-METHYLRAUMACLINE, Journal of the Chemical Society, Chemical Communications, (13), 1994, pp. 1559-1560
When the homologated nitrile 11 derived from L-tryptophan undergoes a
modified Pictet-Spengler reaction with methyl propynoate, the resultin
g cis-tetrahydro-beta-carboline 12a is ideally functionalised for cycl
isation to the bridged ketonitrile 14; simple functional group modific
ations via the nitrile 15 (structure confirmed by X-ray crystallograph
y) allow convergence with the tetracyclic alpha,beta-unsaturated aldeh
yde 10, which is an advanced intermediate for the synthesis of a range
of bridged indole alkaloids.