Intermolecular Trapping of Oxidopyrylium Ylides Applications of FMO Theory for the Rationalization of Product Regio- and stereochemistries Orbital Theory of Dipolar-Dipolarophile Cycloadditions Carbonyl Ylides have very small HOMO-LUMO gaps 30-135°C Hendrickson, J. B; Farina, J.A. J. Org. Chem. 1980, 45, 3359-3361. herefore, either raising the dipolarophile HOMo (electron-donating substituents)or lowering the LUMO (electron-withdrawing)will accelerate LUMO EtN RT R= Ph 5 Endo product as a result of secondary orbital overlap Sammes, P. G: Street, L J. J. Chem. Soc., Perkin Trans. I. 1983, 1261-1265 35B-04 Ylides3/16/934:40PM- - + Intermolecular Trapping of Oxidopyrylium Ylides: Applications of FMO Theory for the Rationalization of Product Regio- and Stereochemistries Endo product as a result of secondary orbital overlap , Et3N, RT R = Ph, OEt Sammes, P. G.; Street, L. J. J. Chem. Soc., Perkin Trans. I. 1983, 1261-1265. 130-135 °C 69% 4:1 exo:endo Generally low yields with electron-poor olefins. Hendrickson, J. B.; Farina, J. A. J. Org. Chem. 1980, 45, 3359-3361. R = OEt; 56% R = Ph; 65% LUMO HOMO HOMO LUMO Orbital Theory of Dipolar-Dipolarophile Cycloadditions 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. O O O O R AcO R O O O O O O O H O O O O H O EtO 35B-04 Ylides 3/16/93 4:40 PM