Synthesis of (±)- and (−)-botryodiplodin using stereoselective radical cyclizations of acyclic esters and acetals

Abstract

Three different routes for the stereoselective synthesis of botryodiplodin have been investigated. The intramolecular allylation of acetals proved to be unsatisfactory due to unstable intermediates and poor stereocontrol. Zard intramolecular radical allylation of a 2-iodopropionate derivative allows the development of an expeditious synthesis of racemic botryodiplodin. The relative configuration within the final product was corrected by a deprotonation–reprotonation step. The cyclization of allenyl bromoacetals was investigated next and proved to be satisfactory for the synthesis of racemic and enantiomerically pure botryodiplodin. Good stereocontrol was achieved by cyclizing a gem-dibromide followed by the stereoselective reduction of the thus formed cyclic monobromide.