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C=C bond forming reactions

C=C bond forming reactions. 1. b- Elimination. X=halogen, sulfonate, amminium, sulfonium : basic condition --- anti elimination. X=OH : acidic condition --- rearrangement occurs. 1. b- Elimination. 2. Pyrolytic syn -elimination --- retro-ene reaction. 300 ㅇ C. 100 ㅇ C.

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C=C bond forming reactions

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  1. C=C bond forming reactions 1. b-Elimination X=halogen, sulfonate, amminium, sulfonium : basic condition --- anti elimination X=OH : acidic condition --- rearrangement occurs

  2. 1. b-Elimination

  3. 2. Pyrolytic syn-elimination --- retro-ene reaction 300 ㅇC 100 ㅇC Chugaev reaction 100 ㅇC

  4. 2. Pyrolytic syn-elimination --- retro-ene reaction < 100 ㅇC Room Temp. General procedure

  5. 3. Fragmentation b-fragmentation t-BuLi, ether 예외

  6. Grob fragmentation : ACIE, 1969, 8, 535

  7. 4. Others From Hydrazone Bamford-Stevens rxn. JCS 1952, 4735 Shapiro rxn. Org. Rxn. 1976, 23, 405 From Diol Corey, TL, 1982, 23, 1979

  8. 3. Wittig Reaction Chemistry of Ylides Ylide : Formation of phosphorous Ylides R= Alkyl : base = BuLi, LDA E.W. NaOH

  9. 3. Wittig Reaction Stereoselectivity with non-stabilized ylides --- cis major non-polar solvent, salt free condition (HMPA) destabilizing phosphorous -- this is not exactly correct with stabilized ylides --- trans major

  10. with non-stabilized ylides 80%, >98% cis

  11. mechanism + betain [2+2] cis olefin

  12. Schlosser modification -70oC trans:cis > 97:3 ACIE, 1966, 5, 126

  13. For Hindered carbonyls Conia procedure Alcohol ensures the equilibrium between ketone and enolate Modhephene Anion of ylide 87% Corey, TL, 1985, 26, 555

  14. with stabilized ylides mechanism

  15. Effect of a-oxygenation and protic solvent DMF 86 : 14 CHCl3 40 : 60 CH3OH 8 : 92 Helv. 1979, 62, 2091 THF 6 : 94 THF-MeOH (1:1) 93 : 7 TL. 2004, 45, 3925

  16. Conjugate addition

  17. 3.2 Wadsworth-Honer-Emmons reaction E-selective trans Water soluble ! W = CN, COOR, CHO, SO2Ph, C(O)R, Ph, vinyl not with Alkyl or H Does not eliminate spontaneously !

  18. Preparation of the reagent Arbuzov reaction : Perkow reaction

  19. cis selective olefination Z:E = 50:1 W.C. Still, TL, 24, 4405(’83) Z:E = 9:1 JOC, 64, 8406 (’99)

  20. Stereo-selective olefination : Horner-Wittig reaction R’COOEt

  21. Enantio-selective olefination > 99 : 1 Hannesian, TL, 33, 7659 (1992) 92 : 8 Masamune, TL, 37, 1077 (1996)

  22. 4. Peterson olefination Gillman, JOC, 27, 3647(’62) Peterson JOC, 33, 780 (’68)

  23. and its diastereomer !

  24. 5. Julia coupling trans major 2 ~ 3 step sequence ! One step via

  25. 5. Julia coupling trans major TL, 1545(1975)

  26. 6. Ramber-Backlund reaction JACS, 114, 7360(’92) 32 – 52 % 94 %

  27. 7. McMurry Coupling Pinacol coupling Mg SmI2 Mg-TMSCl 77%, E:Z = 7:3 McMurry, Chem. Rev. 89, 1513 (’89) Ziegler, JOC, 47, 5229 (’82) 56% 38% TL. 24, 1885 (’83)

  28. 8. Neutral methylenation TiCl4-Zn-CH2I2 TL, 2417(’78) a. Oshima-Lombardo reagent JACS, 108, 7408 (’86) 90% JACS, 119, 1127 (’97) b. Takai alkenylation JACS, 115, 2268 (’93)

  29. Working through Metathesis 9. Transition metal chemistry : neutral olefination Tebbe, JACS, 100, 3611, 1978 a. Tebbe’s reagent Neutral, reactive Unstable, limited X= H, R Pine, Grubbs, JACS, 102, 3270, 1980 X= OR, SR, NR2

  30. b.Petasis reagent JACS, 112, 6392, (1990) R can be TMS 82% TL, 36, 3619 (1995)

  31. c. Olefin Metathesis Grubbs, Tet., 60, 7117, 2004 Metathesis Olefin Metathesis JACS, 90, 4133, 1968 JACS, 92, 528, 1970

  32. JACS, 108, 855, 1986

  33. Schrock cat. Reactive, unstable Grubbs 1st gen.cat./ 2nd gen.cat. Reactive, stable T, 55, 8141, 1999 mechanism

  34. Nicolaou, JACS. 1997, 119, 7960 Smith III, JACS. 2000, 122, 4985

  35. Synthesis of Epoxides a. Sulfur ylide chemistry Sulfur Ylide Sulfonium salt Corey, JACS, 87, 1353, 1965

  36. C. Johnson, JACS, 95, 7424, 1973 Thermodynamic kinetic

  37. Cyclopropanation with Sulfur ylide Soft Nu Hard Nu 81% 89% 75%

  38. Asymmetric Epoxidation with Sulfur ylide C. Johnson, JACS.1973, 7424 Trost,JACS1973, 962 JOC.1989, 4222 97% e.e. Tet. Asym.1996, 1783

  39. Catalytic Asymmetric Epoxidation with Sulfur ylide

  40. Application 배임혁, ACIE, 42, 3274 (’03) 배임혁, Tet., 60, 9725 (’04)

  41. Synthesis of Epoxides b. Darzen Condensation

  42. Asymmetric Darzen Condensation A. Ghosh, OL, 6, 2725 (’04) Extension of the reaction Org. Syn., Coll V 4, 459, (’63)

  43. Homework Chapter 2 :4, 7,14, Due : May, 11

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