D A. Evans [2, 3-Sigmatropic Rearrangements: Olefin Geometi Chem 206 Trisubstituted olefins via [2, 3]-rearrangement of sulfoxides a Trisubstituted olefins via [2, 3]-rearrangement of sulfonium ylides Cuso R1 Grieco,JOc1973,38,2572 ((z>90:10(70 (Z)-path I procedure for the direct synthesis of sulfur ylides R pKa- 18(DMSO a=90:10(95%) a Trisubstituted olefins via Wittig [2, 3]-rearrangement Accts. Chem. Res. 1974, 7, 147-55 C5H11 IO CO2H Nakai. Tet Let 1981, 22, 69 NH MeoH However, this reaction is not general (E(z)>973(80-85% 25°cMe (B区z)3169 equivalent to: () HO CO2 Me H OHMe N S N Me S O R1 Me Ar n-BuLi N Me N S Me Li H PhS O H H R1 Me H R1 O S H H Me Ph Br Me Me OH Me Me Me N Me N S Me Me H OH Me N S N Me Me Me O Me Me N Me N S Me O S R1 Me Ph RCO3H R1 S O Me Ph Bu S Ph Me Me O C5H11 CO2H CO2Me Me O Me N2 C(COOMe)2 S R R CuSO4 :CR2 Me S Ph Bu CO2Me CO2Me C5H11 HO CO2H Me S R R C R R Me HO CO2Me Me C R R S R R H Me S Bu Ph CO2Me CO2Me Trisubstituted olefins via [2,3]-rearrangement of sulfoxides: However, this reaction is not general: LDA (E):(Z) 31:69 Nakai, Tet Let 1986, 27, 4511 Nakai, Tet Let 1981, 22, 69 (E):(Z) > 95:5 (74%) 2 LDA ■ Trisubstituted olefins via Wittig [2,3]-rearrangement: pKa ~ 18 (DMSO base + + – + A general procedure for the direct synthesis of sulfur ylides: Grieco, JOC 1973, 38, 2572 (E):(Z) > 90:10 (70%) ■ Trisubstituted olefins via [2,3]-rearrangement of sulfonium ylides: – + 100 °C (–) is operationally equivalent to: (–) Accts. Chem. Res. 1974, 7, 147-55 [2,3] a a/g = 90:10 (95%) g a (E):(Z) > 97:3 (80-85%) 25 °C Et2NH, MeOH – (Z)-path (E)-path ‡ ‡ D. A. Evans [2,3]-Sigmatropic Rearrangements: Olefin Geometry Chem 206 favored disfavored