D. A. Evans [2,31-Sigmatropic Rearrangements: Olefin Geometry Chem 206 a Starting olefin:(E)Trisubstituted a(Z selectivity has been observed: Still JACS 1978, 100, 1927 (E)-path 95%,>96%(2 Me-78°c ()-path halogen Still says that the TS is early, so that the 1, 2 interactions in the TS are most Rr-Me interaction can destabilize the()transition state while(4 Ts might be destabilized by R, interactions with both X-y and allyl moiety C,Ho. M ■ Starting olefin:(2) CH favored CH2-Li C491 ()-path disfavored R2 a() selectivity has also been observed by others: Sato JACS 1990, 112, 1999 Conclusions 76%区z)(E955 J Olefin geometry dictates sense of asymmetric induction in rearrangement u(4 olefin rearrangements might exhibit higher levels of 1, 3 induction NMe2 J Product olefin geometry can be either(E)or(Z) from(E)starting material Cs-F in HMPA u Product olefin geometry will be(E)from(2) starting material Mei chams 61%(E)(2)1000N + Me Me Me Me N + Me Me CH2–TMS Me X R1 R2 Y: Me X Y: R1 R2 Me X Y R2 H H R1 Me R1 Y X H H R2 Me H R1 R2 X Y H Me H X Y H R2 R1 Me Y :X R1 R2 Me R1 R2 :X Y Me R2 R1 :X Y Me Y :X R1 R2 Me Me O n-Bu CH2–Li O SnBu3 Me n-Bu n-Bu Me O Li n-BuLi KH H Me O H2C H H Li C4H9 Me H C4H9 H O H2C H Li n-Bu Me OH n-Bu Me OH Me NMe2 Me NMe2 halogen SnBu3 Me n-Bu LiO CH2 Me CH2 LiO R1 ❏ Olefin geometry dictates sense of asymmetric induction in rearrangement ❏ (Z) Olefin rearrangements might exhibit higher levels of 1,3 induction ❏ Product olefin geometry can be either (E) or (Z) from (E) starting material ❏ Product olefin geometry will be (E) from (Z) starting material ■ Starting olefin: (Z) D. A. Evans [2,3]-Sigmatropic Rearrangements: Olefin Geometry Chem 206 ‡ ‡ R1–Me interaction can destabilize the (E) transition state while (Z) TS might be destabilized by R1 interactions with both X-Y and allyl moiety. ■ Starting olefin: (E) Trisubstituted highly disfavored ‡ favored ‡ Conclusions (E)-path (Z)-path -78 °C ■ (Z) selectivity has been observed: Still JACS 1978, 100, 1927. 95%, >96% (Z) Still says that the TS is early, so that the 1,2 interactions in the TS are most important. (Z)-path (E)-path ‡ ‡ destabilizing ■ (Z) selectivity has also been observed by others: Sato JACS 1990, 112, 1999. -70 °C LHMDS, NH3 76%, (Z):(E) 95:5 X - X - 61%, (E):(Z) 100:0 Cs–F in HMPA 25 °C