Conformational fixation of enolates by intramolecular metal center dot center dot center dot fluorine interaction

[GRAPHICS] Methyl acetates with fluorine containing auxiliaries at their 2 position we re demonstrated to react smoothly with various electrophiles in a re face p referential manner (up to 90% de). This was interpreted as the result of an intermediary enolate constructing a bicyclo[3.3,0] system by the concomita nt intramolecular chelation of a metal with alpha-oxygen and fluorine, resu lting in the auxiliary effectively blocking attack from the opposite si fac e.