1. Chapter 14 ALKENES AND ALKYNES II. Oxidation and Reduction Oxymercuration and Hydroboration Simple Ring Formation

2. Assigned Sections Sections 14.1 through 14.4 (c. 352) Summary (Table 14-1) Skip section 14.3 Sections 14.5-14.13 will be in c. 353

3. Problem Assignment Chemistry 352 and 353 In-Text Problems: 1 – 34b 6 - 8 10-18 End-of-Chapter Problems: 25 - 26 28 – 31 33 – 35 3842 (all but a) 45- 47 19, 20 22 - 2439 – 414448

4. What is Oxidation? Gain of oxygen Loss of hydrogen Skim section between p. 1 and 2 Oxidation

5. epoxidation cleavage glycol formation complete oxidation n + H 2 O OXIDATIONS OF ALKENES

6. What is Reduction? Gain of hydrogen Loss of oxygen reduced

7. Sect. 14.1 Sect. 14.1 EPOXIDES EPOXIDES anti-glycol formation

8. anti glycolepoxide 1) the formation of epoxides, and First we will look at 2) the opening of epoxides to form glycols generally “trans” EPOXIDATION AND ANTI GLYCOL FORMATION

9. Carboxylic Acid Hydrogen peroxide Organic Peroxide A PERACID

10. TWO COMMONLY-USED PERACIDS m-chloroperbenzoic acid (MCPBA) peracetic acid

11. A CONCERTED REACTION epoxide STEREOSPECIFIC EPOXIDATION WITH A PERACID both bonds formed at the same time

12. anti-Glycol Formation EPOXIDATION RING OPENING anti ring opening

13. OPENING EPOXIDES IN BASE See Chapter 12, Section 12.8 S N 2 : hydroxyl attacks at least substituted carbon, anti only SN2SN2 :: : :::: : :.. :: : and on the opposite side STEREOSPECIFIC

14. OPENING EPOXIDES IN ACID See Chapter 12, Section 12.8 for a review. My Chapter 12 webpage give some examples

15. Sect. 14.2 Sect. 14.2 syn-GLYCOL FORMATION

16. syn glycols are made with OsO 4 or KMnO 4 OsO 4 KMnO 4 osmium tetroxide potassium permanganate syn -Glycol Formation

17. H CH 3 H CH 3 OH OH OsO 4 NaHSO 3 2 HO OsO 4 NaHSO 3 H 2 O C C H H CH 3 CH 3 C C OH OH H H CH 3 CH 3 meso SYN ADDITION GIVES CIS GLYCOLS cis remember: addition is syn result is cis cis -2-butene syn conformation

18. syn-Glycol Formation (I) syn hydroxylation osmium tetroxide

19. Both of the hydroxyl oxygens in the glycol come from OsO 4 REDUCED OXIDIZED Mechanism Notice the transfer of 2e - onto Os = REDUCTION

20. syn-Glycol Formation (II) syn hydroxylation potassium permanganate

21. Making epoxides via bromohydrins Bromohydrin (Chapter 8) ( peracid )

22. Skip Sect. 14.3

23. Sect. 14.4 Sect. 14.4OZONOLYSIS

24. Ozone electric discharge or cosmic rays.. : : : EQUIVALENT RESONANCE STRUCTURES + + - -

25. FORMATION OF AN OZONIDE Ozonolysis HYDROLYSIS OF THE OZONIDE (WORKUP) unstable aldehydes or ketones

26. WORKUP PROCEDURES FOR OZONOLYSIS Two types of workup (decomposition of the ozonide) are possible : 1. OXIDATIVEHydrogen peroxide is present 2. REDUCTIVE METHOD A Add Zn and H 2 O or H 3 O + Aldehydes are oxidized to carboxylic acids. Formaldehyde is oxidized to carbon dioxide, which is lost as a gas. METHOD B Reduce the ozonide with Pd / H 2, and then add acid ( H 3 O + ). Aldehydes survive intact and are not oxidized with reductive conditions.

27. EXAMPLES O3O3 Zn / H 2 O 1)O 3 2) H 2 O 2 H 3 O + OR O3O3 1) Pd/H 2 2) H 3 O + REDUCTIVE WORKUP OXIDATIVE WORKUP + + H 2 O

28. AT ONE TIME OZONOLYSIS WAS WIDELY USED FOR STRUCTURE PROOF BY DEGRADATION FOR STRUCTURE PROOF BY DEGRADATION Unknown compound Broken apart ( or degraded ) to simpler pieces that are easier to identify. The original structure can be deduced by reassembling the pieces. “At one time” = before spectroscopy.

29. C 7 H 12 C 7 H 14 1) O 3 / CH 2 Cl 2 2) H 3 O + Pd / H 2 PROBLEM TO SOLVE answer

30. WHAT WAS THE ORIGINAL STRUCTURE ? oxidative workup H2O2H2O2

31. ACETYLENES KMnO 4 or 1) O 3, CH 2 Cl 2 2) H 3 O + Oxidation of acetylenes, whether by KMnO 4 or ozone, normally yields carboxylic acids.

32. Spruce, Cedar, Fir or Pine Forest Terpenes O3O3 NATURAL SOURCES OF SMOG reacts with terpenes temperature inversion traps bioemissions

33. Sect. 14.5 Hydrogenation of Alkenes + CCHH CC HH catalyst The catalyst is Pt, PtO 2, Pd, or Ni (in special cases Ru, Rh, Re) a syn addition reaction fine powder, very porous, suspended in solution

34. CATALYTIC HYDROGENATION IS COVERED IN SEVERAL PLACES IN THE TEXT, PRINCIPALLY: Ch3 Section 3.18 Hydrogenation of Alkenes Ch4 Section 4.13 Relative Stabilities of Alkenes Ch6 Section 6.12 Heat of Hydrogenation Section 6.13 Resonance Energy of Benzene Ch8 Section 8.11 Hydrogenation of the Double Bond Pages 723-725 (Addition to Triple Bonds) REVIEW OF HYDROGENATION Ch 14 Section 14.4 Hydrogenation of Alkynes

35. Hydrogenation of Alkynes

36. Lindlar is a special catalyst that allows the hydrogenation of an alkyne to stop after one mole of hydrogen is added. quinoline syn addition Most amines, and compounds containing sulfur, reduce the activity of catalysts or “poison” them. Lindlar Catalyst: syn addition

37. Sect 14.6 Dissolving Metal Reduction anti This reaction proceeds with anti addition (trans compound). Catalytic reduction proceeds with syn addition, hence we have a choice of methods.

38. MECHANISM OF Na-LIQUID-NH 3 REDUCTIONS ( from (NH 3 ) n ). - anti addition electron transfer 1 electron transfer 2 +2e +2H + :NH 2 - All intermediates prefer the trans geometry. radical- anion radical anion

39. SODIUM IN LIQUID AMMONIA SODIUM AMIDE IN LIQUID AMMONIA TWO DIFFERENT REAGENTS ! Reducing Agent Strong Base = = NaNH 2 / NH 3 (l) Na / NH 3 (l)

40. Sect. 14.7: Oxymercuration of an Alkene

41. Mechanism of Oxymercuration Formation of Bridged Ion: step 1

42. Step 2: Attack by water

43. Step 3: Reduction

44. Another example Continued next slide

46. Sect. 14.8: Hydroboration of an Alkene

47. Herbert Brown Source: Michigan State University, Department of Chemistry http://www.chemistry.msu.edu/Portraits/PortraitsHH_collection.shtml Nobel Prize, 1979

48. Preparation of Diborane Electron deficient

49. DIBORANE ADDS TO ALKENES ANTI-MARKOVNIKOFF sp 2 empty 2p orbital Since there are 3 B-H bonds, addition can occur three times (3 moles of alkene) Boron adds to the carbon with the most hydrogens (!) which is the reverse of the Markovnikoff Rule. concerted syn addition electrophile RR R substituent stabilizes transient carbocation center hydride transfer anti-Markovnikoff

50. ++  - + - Concerted reaction, no intermediate; syn addition Carbocation intermediate would allow rotation; the reaction would not be stereospecific, giving both syn + anti addition. Concerted versus Carbocation Intermediate RR R

51. Hydroboration of an Alkene a trialkylboron compound ( or a trialkylborane ) 3 moles note abbreviation above bubble B 2 H 6 gas through the solution ““

52. Stereochemistry of Hydroboration Syn-additiion

53. Sect. 14.9: Hydroboration - Protonolysis

54. Sect. 14.10: Hydroboration - Oxidation

55. H2O2H2O2 OH - B(OH) 3 + trialkylborane alcohol ( 3 moles) basic hydrogen peroxide trialkoxyborane 3 3 3 acid H3O+H3O+ This work up step hydrolyzes the trialkoxyboron compound.

56. .. :: H-O-O-H + OHO-O-H + H-O-H ::.. : - -- - hydroperoxide ion trialkoxyborane 2 more times internal S N 2 - adds into empty orbital cast-off

57. Stereochemistry of Hydroboration-Oxidation syn addition retains cis stereochemistry cis syn H3O+H3O+ (work up)

58. Summary of Hydroboration Reactions

59. Hydroboration-Protonolysis of Alkynes Only one pi bond reacts A second reaction sequence is required to react the second pi bond.

60. Hydroboration - Oxidation of Alkynes unfavored tautomer ! Enol Ketone ‘ Only one pi bond reacts immediate tautomerism CCR R' CC R H R' B ‘ CC R H R' OH 3+ BH 3 3 H 2 O 2 / OH _ H3O+H3O+

61. OXYMERCURATION VS. HYDROBORATION-OXIDATION OXYMERCURATION HYDROBORATION-OXIDATION 1) Hg(OAc) 2 2) NaBH 4 1) B 2 H 6 2) H 2 O 2, NaOH Markovnikoff Additionanti-Markovnikoff Addition antisyn result similar to 3M H 2 SO 4 /H 2 O 3) H 3 O +

62. SYNTHESIS PROBLEM Show how to synthesize all five compounds from acetylene and methanol. Requires both Na / NH 3 ( liq ) and NaNH 2 / NH 3 ( liq ). and cis isomer

63. Sect. 14.11: The Diels-Alder Reaction

64. Otto Diels and Kurt Alder Source: Michigan State University, Department of Chemistry http://www.chemistry.msu.edu/Portraits/PortraitsHH_collection.shtml

65. HOMO LUMO Diels-Alder Reaction Diels-Alder Reaction The reaction is concerted - all of the orbitals are aligned in a 6-ring. The HOMO of the diene donates elec- trons into the LUMO of the dienophile. Push Pull

66.       LUMO HOMO BUTADIENEETHYLENE

67. DieneDienophileA Cyclohexene  Works best if the dienophile has electron-withdrawing groups and the diene has electron-donating groups. The HOMO of the diene donates electrons into the LUMO of the dienophile. pull EXAMPLE - WITH ELECTRONIC FACTORS push

68. FORMATION OF A BICYCLIC COMPOUND 

69.  

70. Sect. 14.12: Carbene formation and reactions Carbenes are divalent carbon atoms Carbenes are electrophiles and react readily with double bonds Carbenes add syn to alkene Carbene addition is usually stereospecific

71. Formation of dichlorocarbene

72. Reactions of dichlorocarbene with alkenes

73. Diazomethane reactions

74. Another diazomethane reaction Light

75. Sect. 14.13: Carbenoid reactions These reactions are like carbene reactions, but do not give formal carbenes as intermediates. An example is the Simmons-Smith reaction that uses Zn-Cu couple and CH 2 I 2 Products formed from carbenoid reactions are identical to those from pure carbene reactions. syn-addition to alkene and stereospecific.

76. Simmons-Smith Reaction