Abstract : The first part of this work describes a formal asymmetric synthesis of (+)-anatoxin-a, a neurotoxic alkaloid from Anabaena flos aquae. The synthetic approach is based on highly diastereoseletive [2+2] cycloaddition of dichloroketene and a chiral enol ether. Also an intramolecular cyclisation of a N-acyl iminium intermediate has been achieved in order to construct the azabicyclic core of the natural product.
In the second part, we have developped a new synthesis of racemic camptothecin. This pentacyclic alkaloid isolated from Camptotheca acuminata, was found to be a potent antitumor agent due to the inhibition of topoisomerase I. In this approach, a [3+2] cycloaddition reaction of an isomunchnone, Suzuki coupling and cyanosilylation followed by intramolecular Pinner reaction were used as key-steps.