D. A Evans. M. Dart Epoxides as Electrophiles Chem 206 CONFORMATIONAL EFFECTS IN EPOXIDE RING OPENINGS INDUCT/VE STERIC AND CONFORMATIONAL FURST-PLATTNER RULE EFFECTS IN EPOXIDE RING OPENINGS Acidic catalysis only product Basic catalysis Consider a rigid cyclohexene oxide system OMe Inductive withdrawal of electron density by the C-1ethereal oxygen favors attack at C-3 Conformationally and A100% D 10% Conformationally inductively favor on thes e mple model, the transition-state leading to 1 involves diaxial opening epoxide ring and is chainlike B0% However, formation of diequatorial isomer 2 requires a boat-(or skew)like Inductively favored ransition-state. Therefore, according to the Furst-Plattner rule, diaxial opening of the epoxide ring to afford the diaxial product 1 is preferred annard. R.A. B. Casselman. A.A.. Hawkins. L.R. Can. J. chem. 1965. 43 2398 Bannard, R. A. B; Casselman, A. A Langstaff, E J; Moir, R. Y. Can J. Chem. 1968, 46, 35. Buchanon, J. G. Sable, H Z. In" Selective Organic Transformations Thyagarajan, B S, Ed. Wiley: New York, 1972: Vol 2, p 1O Me H Nu OH H H H Me HO Nu H O H H O H O Nu - Nu HO H H O OR O OR OR Nu OH OR OH Nu OR OH Nu OR Nu OH H O OR Nu HO OR O H OR O OR H OR H O OR HO Nu OR HO Nu HO OR Nu B C A D C D B A INDUCTIVE, STERIC, AND CONFORMATIONAL EFFECTS IN EPOXIDE RING OPENINGS Bannard, R. A. B.; Casselman, A. A.; Hawkins, L. R. Can. J. Chem. 1965, 43, 2398. Bannard, R. A. B.; Casselman, A. A.; Langstaff, E. J.; Moir, R. Y. Can. J. Chem. 1968, 46, 35. Conformationally and inductively favored Conformationally favored 0 % 100 % 10 % 90 % Inductively favored Nu￾Nu￾Nu￾Nu￾Inductive withdrawal of electron density by the C-1ethereal oxygen favors attack at C-3. 1 2 3 1 3 2 NH3 OMe￾Basic catalysis Cl￾Br￾OAc￾OMe￾Acidic catalysis 90 % 10 % only product Nu￾Nu￾Nu- 1 2 In this simple model, the transition-state leading to 1 involves diaxial opening of the epoxide ring and is chairlike. However, formation of diequatorial isomer 2 requires a boat- (or skew) like transition-state. Therefore, according to the Fürst-Plattner rule, diaxial opening of the epoxide ring to afford the diaxial product 1 is preferred. Consider a rigid cyclohexene oxide system: CONFORMATIONAL EFFECTS IN EPOXIDE RING OPENINGS FÜRST-PLATTNER RULE Buchanon, J. G.; Sable, H. Z. In "Selective Organic Transformations"; Thyagarajan, B. S., Ed.; Wiley: New York, 1972: Vol 2, p 1. D. A. Evans, M. Dart Epoxides as Electrophiles Chem 206