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Zero, one, or two electron intermediates

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Zero, one, or two electron intermediates

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    1. Chapter 10 Zero, one, or two electron intermediates!!!

    2. 1st of the 1st

    3. ‘d,l-Dammarenerdiol

    4. Cyclization

    5. Completion

    14. Scheme 10.1 Polyene Cyclizations WS Johnson & others

    15. Polyene Cyclization 10.1

    16. a,?-diols for Rearrangement: Pinacols

    17. Diazoalkane Insertions: toward guaiazulene sesquiterpenes (JA Marshall)

    18. Remainder of Scheme 10.2

    19. Different Catalysts

    20. a-Halo Ketones; Favorskii Rearrangement Ring contraction through 1,3-dipolar intermediates Or semi-benzylic in absence of aacidic proton

    21. Ramberg-Bäcklund: a-Halo Sulfones L.A. Paquette synthesis of propellers

    22. Base-Catalyzed Rearrangements: 10.3

    23. Fragmentation Reactions Taxol Synthesis JACS, 110(19), 6558(1988) Cornerstone of the synthesis is the Titanium iso-propoxide catalyzed rearrangement of 12 in to 13

    24. Carbenes Singlet or Triplet carbenes Generate by a-elimination

    25. Generation of Carbenes: N-Nitroso derivatives of amides or sulfonamides

    27. Carbene Insertion Mechanisms

    28. Diazo Decomposition to Carbenes

    29. Grob Fragmentation A. Grob, Angew. Chem. Int. Ed., 8:535(1969) Base catalyzed C-C cleavage of Y-C-C-A-X into +Y=C + C=A + X- Almost reverse Claisen condensations

    30. 10.4

    32. Simmons Smith Zn-Cu alloy to give X-CH2-Zn-X intermediate Simmons& Smith JACS, 80:5323(1958) JOC, 42(18),3031(1977) – Direction of addition

    33. Catalysts Control Insertion Rh2(acam)4; acetomido Tertiary insertion Rh2(O2CC4F9)4 Mixture of products

    34. Ylides by Carbenoid Decomposition Padwa, G. Fryxell, JOC, 54(4), 817, 1989 Generalized

    35. Insertion Reactions: 10.5

    36. Insertion Reactions: 10.5

    37. Insertion Reactions: 10.5

    38. Insertion Reactions: 10.5

    39. Scheme 10.5 Con.

    40. Copper Catalysts

    41. Scheme 10.7

    42. End of 10.7

    43. Wolff Rearrangement:a-diazoketones 3 possible reaction pathways Concerted Carbene(p641) Oxirene Cyclic a-diazoketones lead to ring contraction Utility of acyclic leads to one carbon homologation

    44. Reaction Pathways

    45. Wolff Rearrangements:

    46. Curtis Rearrangement: Initial product isocyanate Trap by either water to amine; R-NH2 Or alcohol to oxamide: R-NH-CO-OR’ Preparation: Carboxylic acid with ethyl chloroformate then rx. with azide Or Carboxylic derivative with hydrazine followed by nitrite

    49. Schmidt: Scheme 10.9

    50. Schmidt Acids and esters converted to amines via loss of carbonyl Addition of HN3 to acid or ester Migrating group retains configuration

    51. Beckmann Rearrangement

    52. Hoffman Rearrangement

    53. What do you call Democrats out on bond?

    54. Free Radicals

    55. Chapter 10 – Part II Free radicals to C=C bonds R · + C=C to R-C-C· Free radicals to C=O bonds R · + C=O to R-C-O·

    56. Sources of Free Radicals Initiator plus trialkyltin hydride (R3)Sn· R-X + (R3)Sn· to give R· + (R3)Sn-Cl Acyl-selenides + (R3)Sn· to give Acyl· Cyclization to ring compounds

    57. More Radicals Alkyl iodides via reaction with R· from the reaction of oxygen and trialkylboranes HCB Tet. Lett. 29,1041(1988) Alkylmercury plus NaBH4 reductively gives R· and Hgo Remember Halogenations via Free radicals to come

    58. Scheme 10.10

    59. G Stork – 5-Exo vs 6-Endo

    60. Scheme 10.12 Samo - Samo

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