Effect of allylic CH3-nFn groups (n=1-3) on pi-facial diastereoselection

[GRAPHICS] Michael addition of various enolates toward gamma -CH3-nFn-alpha,beta -unsa turated ketones (n = 1-3) was proven to smoothly furnish the 1,4-adducts wi th high si face selectivities which monotonously decreased by reduction in the number of fluorines. Although the Felkin-Anh model correctly anticipate s the present stereochemical outcome only with E-acceptors, the hyperconjug ative stabilization of transition states by electron donation from the ally lic substituents (the Cieplak rule) successfully explains the pi -facial pr eference of both acceptors at least in a qualitative level.