Effect of Allylic CH<sub>3</sub><sub>-</sub><i><sub>n</sub></i>F<i><sub>n</sub></i> Groups (<i>n</i> = 1−3) on π-Facial Diastereoselection
作者:Takashi Yamazaki、Tatsuro Ichige、Satoshi Takei、Seiji Kawashita、Tomoya Kitazume、Toshio Kubota
DOI:10.1021/ol016401g
日期:2001.9.1
[GRAPHICS]Michael addition of various enolates toward gamma -CH3-nFn-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.