Synthesis of vinca alkaloids and related compounds.: Part 108:: Efficient convergent synthetic pathway to the ibophyllidine skeleton IV.: First synthesis of (±)-18-hydroxy-20-epiibophyllidine

The first total synthesis of the pentacyclic alkaloid (+/-)-18-hydroxy-20-epiibophyllidine was realized via an efficient preparation of the D-seco-pseudoaspidospermane molecule. The key step of the sequence involves an intramolecular [4+2] cycloaddition reaction of the dihydrosecodine intermediate, which was built up from the reaction of a tryptamine derivative with an aldehyde-ester. After full epimerization, the intramolecular N-alkylation of the tetracyclic ester gave the pentacyclic compound. Reduction of the latter molecule led to the title compound. (C) 2007 Elsevier Ltd. All rights reserved.