Effect of allylic CH(3-n)F(n) groups (n = 1-3) on pi-facial diastereoselection.
[structure: see text]. Michael addition of various enolates toward gamma-CH(3-n)F(n)-alpha,beta-unsaturated ketones (n = 1-3) was proven to smoothly furnish the 1,4-adducts with high si face selectivities which monotonously decreased by reduction in the number of fluorines. Although the Felkin-Anh model correctly anticipates the present stereochemical outcome only with E-acceptors, the hyperconjugative stabilization of transition states by electron donation from the allylic substituents (the Cieplak rule) successfully explains the pi-facial preference of both acceptors at least in a qualitative level.
Yamazaki
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Department of Bioengineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan. tyamazak@bio.titech.ac.jp
Ichige
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Takei
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Kawashita
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Kitazume
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Kubota
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