Polyene cascade cyclizations mediated by BF3·CH3NO2· an unusually efficient method for the direct, stereospecific synthesis of polycyclic intermediates via cationic initiation at non-functionalized 3° alkenes. An application to the total synthesis of (±)-taxodione

Article abstract of DOI:10.1016/S0040-4020(01)85502-2

Convenient stock solutions of BF₃ gas in nitromethane have been shown to promote "H⁺ catalyzed" polyene cyclizations that proceed with excellent levels of regio- and stereocontrol. A direct comparison of this new method for effecting cationic polyannulations to several modern as well as classical procedures has conclusively defined the preparative advantages of the BF₃·CH₃NO₂ medium. The utilization of these new conditions for cationic polycyclization in a concise total synthesis of the antineoplastic agent (±)-taxodione is described.