D. A. Evans. M. Dart Epoxides as Electrophiles Chem 206 REGIOSELECTIVITY OF EPOXIDE RING OPENINGS CONFORMATIONAL EFFECTS IN EPOXIDE RING OPENINGS EFFECT OF CONJUGATING SUBSTITUENTS FURST-PLATTNER RULE H2S04, acetone e only product no cis diol observed Henbest, H B, Smith, M; Thomas, A. J. Chem. Soc. 1958, 3293 Rickborn, B; Murphy, D K J. Org. Chem. 1969, 34, 3209 H= LAIH H= LiAlH4 with Xs AlCl Anomalous result with the p-NO2 derivative: a prion one would expect more attack at C-B than C-a. Fuchs. R: VanderWerf. C. A. J. Am. chem. Soc. 1954.76. 1631-1634 Morand. P Can arker, R. E. Isaacs, N S. Chem. Rev. 1959, 59. 737-799 F=< LiAIHg Furst, A, Plattner, P. A. He/v. Chim. Acta 1949, 32, 275 Alt, G H: Barton D H R. J. Chem. Soc. 1954. 4284 (39t93%) The major product in the reactions of rigid cyclohexene epoxides is ble for the regioselectivity observed derived from diaxial ning opening 1. The ole, H. Z. In"Selective Organic Transformations": Thyagarajan, d. T.H. J. Am. Chem Stevens. C. C. H. J. Org. Chem 01O X Me MeO Me O Ph Ph O Me MeO Me R2NH OH X MeO OH Nu Ph Me Me Ph NR2 O Me Me OH X O Me Me H H H Me HO X HO X Me H HX HX O Me H H Me O H H OH Me Me OH LiAlH4 LiAlH4 Me Me OH OH H H HO Me H H Me HO CONFORMATIONAL EFFECTS IN EPOXIDE RING OPENINGS FÜRST-PLATTNER RULE Aq H2SO4 , acetone (90 %) only product no cis diol observed Fürst, A.; Plattner, P. A. Helv. Chim. Acta 1949, 32, 275. Alt, G. H.; Barton, D. H. R. J. Chem. Soc. 1954, 4284. Henbest, H. B; Smith, M.; Thomas, A. J. Chem. Soc. 1958, 3293. Rickborn, B.; Murphy, D. K. J. Org. Chem. 1969, 34, 3209. The major product in the reactions of rigid cyclohexene epoxides is derived from diaxial ring opening. Buchanon, J. G.; Sable, H. Z. In "Selective Organic Transformations"; Thyagarajan, B. S., Ed.; Wiley: New York, 1972: Vol. 2, p 1. Stevens, C. L.; Coffield, T. H. J. Am. Chem. Soc. 1958, 80, 1919. Stevens, C. L.; Chang, C. H. J. Org. Chem. 1962, 27, 4392. LiAlH4 NaOMe MeOH MeOH, H2SO4 Nu - (39 to 93 %) Conjugative stabilization by oxygen is responsible for the regioselectivity observed in eq 1. The opposite regioselection observed in eq 2 is surprising. 1 2 REGIOSELECTIVITY OF EPOXIDE RING OPENINGS EFFECT OF CONJUGATING SUBSTITUENTS H - a b X = NO2 38 62 Br 84 16 H 74 26 OMe 5 95 H 100 0 OMe 80 20 H 2-10 90-98 H - = LiBH4 H - = LiAlH4 H - = LiAlH4 with xs AlCl3 Anomalous result with the p-NO2 derivative; a priori one would expect more attack at C-b than C-a. Fuchs, R.; VanderWerf, C. A. J. Am. Chem. Soc. 1954, 76, 1631-1634. Kayser, M. M.; Morand, P. Can. J. Chem. 1980, 58, 302-306. Parker, R. E.; Isaacs, N. S. Chem. Rev. 1959, 59, 737-799. D. A. Evans, M. Dart Epoxides as Electrophiles Chem 206