D. A. Evans. D. Barnes Carbonyl Ylids: Dipolar Cycloaddition Chem 206 Tandem Intramolecular Cyclization-Intermolecular Cycloaddition Reactions of Diazoimides: [3+2] addition R 2(oac)4 e NEC-COEt 00o RCHO DMAD O2CH3 Et SiH/BF3 Et2O Dipolar-Dipolarophile Cycloadditions: HOMO-LUMO Energies Carbonyl Ylides have very small HOMO-LUMO Maier, M. E: Evertz, K. Tetrahedron Lett. 1988. 29, 1677-1680 ylide dipolarophile Therefore, either raising the dipolarophile HOMo (electron-donating substituents )or lowering the LUMo (electron-withdrawing)will accelerat 000 the reaction LUMO HOMO Padwa et. al. Tetrahedron lett. 1992, 33, 4731-4734D. A. Evans, D. Barnes Carbonyl Ylids: Dipolar Cycloaddition Chem 206 O CHN2 O O O R R O NPh R O O O H H O CO2CH3 CO2CH3 R O O N CO2Et R O O O R N C CO2Et R O NPh H O O Tandem Intramolecular Cyclization–Intermolecular Cycloaddition O O HOMO LUMO Dipolar-Dipolarophile Cycloadditions: HOMO–LUMO Energies Carbonyl Ylides have very small HOMO-LUMO gaps Energy ylide dipolarophile Therefore, either raising the dipolarophile HOMO (electron-donating substituents) or lowering the LUMO (electron-withdrawing) will accelerate the reaction. Reactions of Diazoimides: [3+2] addition 74% Et3SiH / BF3 •Et2O CH2Cl2 68% Maier, M. E.; Evertz, K. Tetrahedron Lett. 1988, 29, 1677-1680. O N Bn O H CH3 N Me H Me OH H O Bn O N Me O O O Bn N2 O N Bn O COMe H Me Me PhCH3 , 110 °C O N Bn O COMe Padwa et. al. Tetrahedron Lett. 1992, 33, 4731-4734. "high yield" Rh2 (OAc)4 PhH, reflux N Me O O O N2 N O Me H H O O N O N Me O O N2 N N Me O O O H H H 88% Me Me O RCHO DMAD Rh2 (OAc)4 Rh2 (OAc)4 –N2