D. A. Evans Cycloaddition Reactions-2 Chem 206 Summary of Ketene Cycloadditions 人 c=0 Br Zn PhC=C=O R cH2c CH2 C=0 FMO Analysis Ketene Preparation HOMO sc=o Staudinger Reaction(very gener X=CL Ts AcO. DCC. etc.. (CH3 CO)20 H2C=C=0 ACOH RCH2CO2Ar -,O C=0H2C C O Ph2C C O H C O O ZnBr2 Zn O O D O Ph Br O Ph Br O O O H O R R' O O R R' R' R O R R' R' R O (CH3CO)2O R X O R' C O R R' D H2C C O AcOH OH R O OAr C O R -ArO H2O C O R R' N O R R' Z Y O X R R' X Y Y X O R' R O R' R O 1 R 2 R 3 C O R 1 R 2 R 3 or D R R' O N2 or D C O R R' R O H D -CH2CH2 C O R H HOMO O H H O D R3N RCH2CO2Ar O O R R' D. A. Evans Cycloaddition Reactions-2 Chem 206 Ketene Preparation Staudinger Reaction (very general) X = Cl, Ts, AcO, DCC, etc... + _ _ _ _ _ _ or Alkene Imine R = -CH=CH2 1,3-Dipole Carbonyl Summary of Ketene Cycloadditions 550 °C hn hn [p 2 sp 2 a ] LUMO FMO Analysis