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Stereoelectronic requirement for Ei-type Elimination: abstraction of b H–atom by leaving group

Stereoelectronic requirement for Ei-type Elimination: abstraction of b H–atom by leaving group. "Cope–elimination". "Chugaev Elimination". “near coplanarity". Regioselective Cope-Elimination. “near coplanarity". "Sulfoxide (Selenoxide)–elimination". “Enone Synthesis".

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Stereoelectronic requirement for Ei-type Elimination: abstraction of b H–atom by leaving group

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  1. Stereoelectronic requirement for Ei-type Elimination: abstraction of b H–atom by leaving group "Cope–elimination" "Chugaev Elimination" “near coplanarity"

  2. Regioselective Cope-Elimination “near coplanarity" "Sulfoxide (Selenoxide)–elimination" “Enone Synthesis"

  3. Synthesis of a-methylene-g-lactone opportunity trans cis

  4. “Peterson Olefination"

  5. “Nozaki-Yamamoto Elimination for Regio- and Stereo-defined Allylic Alcohol Synthesis from Epoxides" acis-base hybrid reagent (A-B reagent)

  6. Stereoelectronic Requirements:SUMMARY sp3, sp2, and sp Reaction Centers Attacked by X– a sp3 sp2 a a a sp Epoxides and related a endo a exo X should be second periodical elements

  7. Stereoelectronic Control in Nature: Polyene–Epoxide Cyclization squalene squalene epoxide H+ lanosterol cholesterol

  8. Biomimetic Polyene–Alcohol Cyclization: Strategy for Stereoselective Steroid Synthesis: W. S. Johnson Biomimetic Synthesis: learning from nature HOH H+ Ozone KOH progesterone

  9. Baldwin Rule exo-cyclization endo-cyclization The First Rule: a) 3~7-Exo–Tet Cyclization : favored b) 5~6-Endo–Tet Cyclization : disfavored (a) (b) "3–Exo–Tet" "5–Endo–Tet"

  10. The Second Rule: a) 3~7-Exo–Trig Cyclization : favored b) 3~5-Endo–Trig Cyclization : disfavored 6~7-Endo–Trig Cyclization : favored (a) (b)

  11. The Third Rule: a) 3~4–Exo–Dig Cyclization : disfavored 5~7–Exo–Dig Cyclization : favored b) 3~7–Endo–Dig Cyclization : favored (a) (b)

  12. The Fourth Rule: (Enol...)-Exo-Tet (a) 3~7–(Enolexo)–Exo–Tet: favored (b) 3~5–(Enolendo)–Exo–Tet: disfavored (c) 6~7–(Enolendo)–Exo–Tet: favored (Enolexo)–Exo–Tet The Fifth Rule: (Enol...)-Exo-Trig (a) 3~7–(Enolexo)–Exo–Trig: favored (b) 3~5–(Enolendo)–Exo–Trig: disfavored (c) 6~7–(Enolendo )–Exo–Trig: favored (Enolendo)–Exo–Trig 4(b) 5–(Enolendo)–Exo–Tet: disfavored 1(a) 5–Exo–Tet: favored enolate addition C-alkylation (SN2) O-alkylation (SN2)

  13. The Fourth Rule (a): favored The Fourth Rule (c): favored 5–(Enolexo)–Exo–Tet 7–(Enolendo)–Exo–Tet

  14. much faster > not produced 6–Exo–Tet 6–(Enolendo)–Exo–Tet The Fourth Rule (c): favored The First Rule (a): favored

  15. Aryne or Benzyne (Dehydrobenzene) Isolated Carbon-Carbon Multiple Bonds: # very low reactivity towardn-base (very low electrophilicity) # very low nucleophilicity of n-base toward carbon-carbon multiple bonds except for arynes H+

  16. Evidence in support of non-SNAr mechanism cine substitution SNAr Mechamism

  17. Preparation of Arynes: Break Through elimi. fast B– slow excess B- B– slow drawback Break Through: K. Suzuki, 1991 BuLi v. fast elimi. fast + halogen/metal exchange: very fast [4 + 2] cycloaddition 90%

  18. electron withdrawing inductive effect n-BuLi THF, –78℃ <10 min R = Me: 76% R=Bn: 82% K. Suzuki, JACS,1992: Total Synthesis of (+)-Gilvocarcin M Tf2O/DIPEA CH2Cl2 99%

  19. (+)-Gilvocarcin M

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