Abstract
Michael addition reactions of enolates derived from the selected ketone, ester, and amide to γ-CH 3 - n F n -α,β-unsaturated ketones (n=1∼3) were proved to smoothly furnish the desired 1,4-adducts with high level of diastereofacial selectivity, which monotonously decreased by reduction in a number of fluorine involved. Although the Felkin-Anh model can accommodate the stereochemical outcome when E-acceptors were employed, the opposite stereoisomer was obtained from the corresponding trifluorinated Z-isomer. The hyper-conjugative stabilization of transition states by electron donation from the proximate allylic substituents (the Cieplak rule) successfully explains the observed π-facial preference of both E- and Z-acceptors.
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