D.A. Evans The Felkin-Anh Eisenstein model Chem 206 The flaw in the Felkin model: a problem with aldehydes ! Houk: Torsional effects in transition states are more important than in ground states R predicted to be destabilizing O Review Lecture-7 favored Ts H Transition state Hi, F*C-RL Nu: Wrong prediction GC№u Anh Eisenstein Noveau J. Chim. 1977. 1.61-70 Anh Topics in Current Chemistry. 1980, No 88, 146-162 RL a*C-RL Ground state Felkin M R M RL favored R Transition states H-radical and H-anion: antiperiplanar g*C-R orbital stabilized the ts anti-Felkin illustrated for Nu addition M R M RL C-RL C-RL New Additions to Felkin model: oC-Nu :c-nu Dunitz-Burgi C=o-Nu orientation applied to Felkin model The antiperiplanar effect Forming bond Hyperconjugative interactions between C-Rl which will lower T*C=O Forming bond ill stablize the transition state Houk, Science1981,231,1108-1117 Theoretical Support for Staggered Transition states Houk,JAcS1982,104,71626 Houk, Science1986,231,1108-17H H C C H H H Nu C R H Nu C HO H Nu C Nu H OH R L R L R M R M H H C O R L R M R L O R M H H H H C O O C H R L R L R M R M H O C H R L R M C Nu C RL H H RL RL H H D. A. Evans The Felkin-Anh Eisenstein Model Chem 206 wrong prediction destabilizing interaction predicted to be favored TS Nu: Nu: The flaw in the Felkin model: A problem with aldehydes!! Anh & Eisenstein Noveau J. Chim. 1977, 1, 61-70 Anh Topics in Current Chemistry. 1980, No 88, 146-162 anti-Felkin Nu: Nu: Nu: Felkin ‡ ‡ Nu: favored disfavored ■ The antiperiplanar effect: Hyperconjugative interactions between C-RL which will lower p*C=O will stablize the transition state. ■ Dunitz-Bürgi C=O–Nu orientation applied to Felkin model. New Additions to Felkin Model: Theoretical Support for Staggered Transition states Houk, JACS 1982, 104, 7162-6 Houk, Science 1986, 231, 1108-17 Review Lecture-7 Houk: "Torsional effects in transition states are more important than in ground states" sC-Nu s*C-RL Transition state sC-Nu s*C-RL Ground state Transition states H-radical and H-anion: antiperiplanar s*C–R orbital stabilized the TS illustrated for Nu addition Houk, Science 1981, 231, 1108-1117 "The Theory and Modeling of Stereoselective Organic Reactions" sC-Nu s*C-RL sC-Nu homo s*C-RL lumo Forming bond Forming bond