Stereoselective approaches to (E,E,E) and (Z,E,E)-alpha-chloro-omega-substituted hexatrienes: Synthesis of all E polyenes

Two stereocontrolled synthetic approaches to (E,E,E) and (Z,E,E)-alpha-chlo ro-omega-substituted hexatrienes 1-3 are described starting from unsaturate d compounds 4-6. The key step of the first approach is based on the palladi um-catalyzed rearrangement of bis-allylic acetates 4 and 5 and the second o ne is based on the stereoselective reduction of homopropargylic alcohols 6 followed by an elimination reaction. These stable chlorotrienes 1-3 are sui table synthetic intermediates for the construction of navenone B and all E polyenes (trienes, tetraenes, hexaenes and heptaenes). (C) 1999 Elsevier Sc ience Ltd. All rights reserved.