3MeMePh de MeNH2 H2 ID: 316338
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Chiral auxiliariessubstrate(achiral)+chiral auxiliarycouple to form new chiral compoundproductchiral auxiliarysubstrate(achiral)chiral auxiliaryproduct(chiral)chiral auxiliary+cleave chiral auxiliary 3MeMePh de . MeNH2, H2 Ð)-fluoxetineProzac!Cl pcCl!99% e.e.1 recrystallisationOClM LRERRZHLBOLREHRZHLH )¥ Therefore alkene geometry controls the relative stereochemistry (like aldol rct)E-alkene gives anti MeMeMeMeMeM O2HMeMeOHOOOHMeO(+)-SCH 351 (chiral)chiral catalystchiral catalystsubstrate(achiral)chiral catalystStereoselective synthesis: chiral catalysis¥ Chiral catalysis - ideally a reagent that accelerates a reaction (without being destroyed) in a chiral environment thus permitting one chiral molecule to generate millions of new chiral molecules...12substrate(achiral)product(chiral) ¥ An efÞcient catalyst for the reduction of ketones is Corey-Bakshi-Shibata catalyst (CBS) ¥ Allylation works very well with high e.e.¥ Problem with crotylation - often hard to control d.e.¥ Reason is that the reaction proceeds via an open transition state MeNMePNNOOHH( )5RE = Me86% eeanti/syn 99/1RZ = Me95% eesyn/anti �19/1 ees luene, Ð78¡ MeH( e.e.HHH