Cation-stabilizing auxiliaries in polyene cyclizations. 5. The fluorine atom as a cation-stabilizing auxiliary in biomimetic polyene cyclizations. 2. Asymmetric synthesis of a steroid

The use of the fluorine atom an a cation-stabilizing (C-S) auxiliary for enhancing polyene cyclization has been improved in synthetic effectiveness by the demonstration that an acetal 5 can be converted to a racemic fluorocycle, bearing the natural backbone configuration of the steroids