FORBIDDEN 1,2-CARBANION SHIFTS MECHANISM AND APPLICATION OF THE FRITSCH- BUTTENBERG-WIECHELL REARRANGEMENT. Chun Ho Lam

Transcription

1 1 FORBIDDEN 1,2-CARBANION SHIFTS MECHANISM AND APPLICATION OF THE FRITSCH- BUTTENBERG-WIECHELL REARRANGEMENT Chun Ho Lam 17 th November 2010 Chun Ho Lam 17 th November, 2010

2 Contents 2 Section 1: Discovery of the Fritsch-Buttenberg-Wiechell (FBW) Rearrangement Section 2: Mechanistic Probing with Ring Expansion Model The Woodward-Hoffmann Rules Effect of different conditions on the mechanism Investigation of the mechanism Section 3: A recent application of the FBW Rearrangement

3 Section 1 3 Discovery of the Fritsch-Buttenberg-Wiechell (FBW) Rearrangement

4 Introduction of the FBW Rearrangement 4 In 1894, discovered by the 3 scientists: Paul Ernst Moritz Fritsch Wilhelm Paul Buttenberg Heinrich G. Wiechell Fritsch, P. Justus Liebigs Annalen der Chemie 1894, 3, 319. Buttenberg, W. P. Justus Liebig's Annalen der Chemie 1894, 3, 324 Wiechell, H. Justus Liebig's Annalen der Chemie 1894, 3, 337

5 Possible Mechanisms for FBW 5 Route A Route B Route C Fritsch, P. Justus Liebigs Annalen der Chemie 1894, 3, 319. Buttenberg, W. P. Justus Liebig's Annalen der Chemie 1894, 3, 324 Wiechell, H. Justus Liebig's Annalen der Chemie 1894, 3, 337

6 Section 2 Part A 6 Mechanistic Probing with Ring Expansion Model Introduction to the Ring Expansion Model The Woodward Hoffmann Forbidden Transformation

7 Mechanistic Probing Tool 7 Mechanism Probing: Solvent Halide group Temperature Substitute Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

8 Possible Routes 8 Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

9 Elimination of Route A 9 Diels-Alder Trap Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

10 Elimination of Route C 10 Route C Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

11 The Only Way: Route B 11 However: 1. Anionic 1,2-sigmatropic rearrangement 2. Violates the Woodward-Hoffmann symmetry rule 3. This should be impossible Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

12 The Woodward-Hoffmann Rule 12 An anionic sigmatropic rearrangement is a 4e - process

13 13 Molecular Orbital Diagram

14 The Woodward-Hoffmann Rule 14 Definition: Conversation of orbital symmetry in a (concerted) pericyclic reaction Thermodynamically Allowed

15 The Forbidden Examples 15 1,2-Wittig Rearrangement Stevens rearrangement Source: Strategic Application of Named Reaction in Organic Synthesis

16 The Allowed Examples 16 Wagner-Meerwein Rearrangement Beckmann Rearrangement Source: Strategic Application of Named Reaction in Organic Synthesis

17 Route B: The Forbidden Route 17 The only option left: The important factors: 1. Vinyl Anion 2. Vinyl Group 3. Vinyl Anion Stabilizer (Bromine) Erickson, K.L J. Org. Chem. 1973, 8, 1463.

18 Importance of these factors? 18 No Double Bond No Vinyl Anion No Bromine Erickson, K.L J. Org. Chem. 1973, 8, 1463.

19 Polar vs. Non-Polar Solvent 19 In polar solvent: In non-polar solvent: Erickson, K.L J. Org. Chem. 1973, 8, 1463.

20 Isomerization in Polar Solvent 20 Where does come from? Polar solvent can stabilize the charges on the resonance form thereby promotes side reaction. Erickson, K.L J. Org. Chem. 1973, 8, 1463.

21 Quick Summary 21 Route B: The Forbidden Route To trigger Route B, there must be: Halogen Vinyl Anion Strong Base Non-polar solvent

22 Section 2: Part B 22 Mechanistic Probing with Ring Expansion Model ~ Investigation of the FBW rearrangement ~

23 Possible Mechanism for Route B 23 Case 1 Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

24 Possible Mechanism for Route B 24 Case 2: Case 3 Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

25 Elimination of Case 3 25 Case 3 is unlikely at low temperature because The Diels-Alder trap shows Case 3 is not happening at low temperature rearrangement. Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

26 The Remaining: Case 1 and Case 2 26 Case 1: Bromine attach to terminal carbon Case 2: Bromine partially attach to vinyl group Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

27 Distinguish the 2 Cases with 13 C 27 Major Product Cis Trans 13 C labeling reviews the reaction pathway depends on the bromine position Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

28 The Overall Results 28 Cis Trans Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

29 The Overall Results Continued 29 Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

30 Cis to Trans Isomerization 30 ¾ reactions prefer Case 2, the migrating path. ¼ reaction prefers Case 1, the re-hybridization path. Cis Trans Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

31 Isomerization Analysis 31 Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

32 The Cis-Isomer Reaction 32 Isomerization Rehybridization Rotation of 13 C Labeled Carbon Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

33 Quick Summary The trans migration pathway is strongly preferred. 2. Reaction happens in a stepwise rather than a concerted mechanism. W-H Rule Forbid W-H Rule Allow

34 The Role of Halogen in Reaction 34 % Yield A: B F : 1 Cl : 1 Br : 1 I : 1 Du Z.M.; Haglund M. J.; Pratt L. A.; Erickson K.L. J. Org. Chem. 1998, 63, 8880

35 Trend Interpretation 35 Analysis with Newman Projection Du Z.M.; Haglund M. J.; Pratt L. A.; Erickson K.L. J. Org. Chem. 1998, 63, 8880

36 Trend Interpretation at Orbital Level 36 Du Z.M.; Haglund M. J.; Pratt L. A.; Erickson K.L. J. Org. Chem. 1998, 63, 8880

37 Trend Interpretation 37 BDE (kcal mol -1 ): F (117) > Cl (79) > Br (69) > I (51.7) % Yield A: B F : 1 Cl : 1 Br : 1 I : 1 Single Mig. Double Mig. The Halogen dissociated Du Z.M.; Haglund M. J.; Pratt L. A.; Erickson K.L. J. Org. Chem. 1998, 63, 8880

38 Quick Summary 38 The size of Halogen is important to the mechanism The 13 C method system was misleading

39 Stereo fate of the Migrating Group 39 * * * * 1. Complete retention of stereogenic center 2. Double migration > Single migration (Bromine is not on 13 C) 3. High yield is due to tetra-substituted carbon Du Z.M.; Erickson K.L. J. Org. Chem. 2010, 75, 7129

40 The Mechanism Mechanism agrees with 13 C study and Halogen study. 2. Double migration is preferred Du Z.M.; Erickson K.L. J. Org. Chem. 2010, 75, 7129

41 To Conclude the Findings 41 D.A. Trap Halogen Study Ref. Study Du Z.M.; Erickson K.L. J. Org. Chem. 2010, 75, 7129

42 Free Energy (kcal mol -1 ) The MP G(d) Calculation 42 Hal Li C H React TS Int 1 TS 2 Int2 TS 3 Prod Reaction Coordinate Pratt, L.M.; Nguyen N. V.; O. Kwon, Chem. Lett. 2009, 38, 574. F Cl Br

43 Computational results vs. Ring Expansion model 43 Computational Results Carbene Ring Expansion Model Carbene with Halogen F, Cl, Br Makes no difference to migration Intermediate: the migrating group is in the vinyl system F causes 50:50 Single : Double Cl and Br causes mostly Double. Intermediate: the migrating Double Stepwise migration Pratt, L.M.; Nguyen N. V.; O. Kwon, Chem. Lett. 2009, 38, 574.

44 Reliability of the results 44 Reliable Gas phase cond. resemble the non-polar solvent. MP2 gives good estimation of the T.S. and Int Results suggest other mechanism is possible. However The ring strain issue is not addressed The spectator ion is different: Li vs. K Migrating group is H, not alkyl group Pratt, L.M.; Nguyen N. V.; O. Kwon, Chem. Lett. 2009, 38, 574.

45 Summary 45 Mechanism bypasses WH Rule with a rehybridization of the migrating group. Mechanism is minor temp. dependent Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.

46 Summary Continued 46 Mechanism depends on: Solvent polarity Halide size Temperature Geometry of the reactant Du Z.M.; Haglund M. J.; Pratt L. A.; Erickson K.L. J. Org. Chem. 1998, 63,

47 Combining the REM with FBW 47 According to the Ring Expansion Model: Route A

48 48 The Suggested FBW Rearrangement

49 49 The Modified FBW Rearrangement

50 Section 3 50 Recent Application of Modified FBW Rearrangement

51 Application of Modified FBW in Polyyne Synthesis 51 Introduction of Polyyne What it is and what it does Synthesis of Polyyne with traditional Cu/Pd Coupling with FBW rearrangement

52 Introduction of Polyyne 52 Sp 3 -Hybridized Carbon Diamonds Properties 1. Extremely Rigid Sp 2 -Hybridized Carbon Graphite 1. Thermal Conductor 2. Electrical Conductor Sp-Hybridized Carbyne Polyyne 1. Electrical Conductor? 2. Optical Applications?

53 Traditional Polyyne Synthesis 53 Homocoupling Reaction Glaser Coupling Eglinton Modification Hay s Modification Source: Strategic Application of Named Reaction in Organic Synthesis

54 Traditional Polyyne Synthesis 54 Hetercoupling Reaction: Chodkiewitz-Cadiot Sonogashira Cross Coupling Source: Strategic Application of Named Reaction in Organic Synthesis

55 Synthesis of Polyyne with Cu/Pd Coupling 55 Total Steps: 3 Overall Yield: 17% Yamaguchi, M.; Park, H. J.; Hirama, M.; Torisu, K.; Nakamura, S.; Minami, T.; Nishihara, H.; Hiraoka, T. Bull. Chem. Soc. Jpn. 1994, 67, 1717.

56 Synthesis of Polyyne with RBW Rearrangement 56 Total Steps: 4 Overall Yield: 56% 1 pot Luu, T.; Morisaki Y.; Cunningham N.; Tykwinski R. R. J. Org. Chem., 2007, 72, 9622.

57 Limitation of the FBW method 57 Can FBW take over Cu coupling in Polyyne Synthesis? Jahnke E.; Tywinski R.R.; Chem. Commum. 2010, 46, 3235

58 FBW vs. Copper Coupling FBW can be a 1-pot convenient method 2. Copper Chemistry is still an important coupling reaction Jahnke E.; Tywinski R.R.; Chem. Commum. 2010, 46, 3235

59 Conclusion 59 Bypass W-H Rule with Rehybridizations, Radical rearrangement Mechanism of FBW is most likely a double migration process. Computational study disagrees with the experiment Methods with more similar condition should be employed FBW offers 1-pot synthesis of Polyyne At low module of alkyne Copper chemistry still has its importance.

60 Acknowledgement 60 o Dr. Jackson o Dr. Maleczka o Dr. Huang o Dr. Redko, Dr. Saumitra, Abby, Crystal, Laura, Megan, Melisa, Meisam, San, Xin, Zhe, members from Baker and Wulff s group 60