Circumtrindene: A geodesic dome of molecular dimensions. Rational synthesis of 60% of C60

Journal of the American Chemical Society

Volumn 122, Issue 12, 2000, Pages 2719-2724

  Ansems, Ronald B M ^a   Scott, Lawrence T ^a  

^a BOSTON COLLEGE   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ALKENE; KETONE; NAPHTHALENE DERIVATIVE; POLYCYCLIC AROMATIC COMPOUND;

ARTICLE; CRYSTAL STRUCTURE; NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY; OLIGOMERIZATION; PYROLYSIS; SYNTHESIS;

EID: 0034728627     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja993028n     Document Type: Article

References (83)

1. Aspects of this work have been reported previously in preliminary accounts: (a) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Presented at the Ninth International Symposium on Novel Aromatic Compounds, Hong Kong, August 1998 (Nozoe Memorial Lecture). (b) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Fourteenth International Conference on Physical Organic Chemistry, Florianópolis, Santa Catarina, Brazil, August 1998; Abstract IL5C. (c) Ansems, R. B. M.; Bratcher, M. S.; McComas, C. C.; Scott, L. T. Abstracts of Papers, 216th National Meeting of the American Chemical Society, Boston, MA; American Chemical Society: Washington, DC, 1998; Abstract ORGN 103. See also refs 3f and 3g.
2. Aspects of this work have been reported previously in preliminary accounts: (a) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Presented at the Ninth International Symposium on Novel Aromatic Compounds, Hong Kong, August 1998 (Nozoe Memorial Lecture). (b) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Fourteenth International Conference on Physical Organic Chemistry, Florianópolis, Santa Catarina, Brazil, August 1998; Abstract IL5C. (c) Ansems, R. B. M.; Bratcher, M. S.; McComas, C. C.; Scott, L. T. Abstracts of Papers, 216th National Meeting of the American Chemical Society, Boston, MA; American Chemical Society: Washington, DC, 1998; Abstract ORGN 103. See also refs 3f and 3g.
3. Aspects of this work have been reported previously in preliminary accounts: (a) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Presented at the Ninth International Symposium on Novel Aromatic Compounds, Hong Kong, August 1998 (Nozoe Memorial Lecture). (b) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Fourteenth International Conference on Physical Organic Chemistry, Florianópolis, Santa Catarina, Brazil, August 1998; Abstract IL5C. (c) Ansems, R. B. M.; Bratcher, M. S.; McComas, C. C.; Scott, L. T. Abstracts of Papers, 216th National Meeting of the American Chemical Society, Boston, MA; American Chemical Society: Washington, DC, 1998; Abstract ORGN 103. See also refs 3f and 3g.
4. (a) Scott, L. T.; Hashemi, M. M.; Meyer, D. T.; Warren, H. B. J. Am. Chem. Soc. 1991, 113, 7082-7084.
5. (b) Scott, L. T.; Hashemi, M. M.; Bratcher, M. S. J. Am. Chem. Soc. 1992, 114, 1920-1921.
6. (c) Borchardt, A.; Fuchicello, A.; Kilway, K. V.; Baldridge, K. K.; Siegel, J. S. J. Am. Chem. Soc. 1992, 114, 1921-1923.
7. Several reviews have already been published: (a) Rabideau, P. W.; Sygula, A. In Advances in Theoretically Interesting Molecules; Thummel, R. P., Ed.; JAI Press: Greenwich, 1995; Vol. 3, pp 1-36. (b) Rabideau, P. W.; Sygula, A. Acc. Chem. Res. 1996, 29, 235-242. (c) Scott, L. T. Pure Appl. Chem. 1996, 68, 291-300. (d) Mehta, G.; Rao, H. S. P. Adv. Strain Org. Chem. 1997, 6, 139-187. (e) Mehta, G.; Rao, H. S. P. Tetrahedron 1998, 54, 13325-13370. (f) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Atual. Fis.-Quim. Org. 1999, 11, 138-150. (g) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Pure Appl. Chem. 1999, 71, 209-219.
8. Several reviews have already been published: (a) Rabideau, P. W.; Sygula, A. In Advances in Theoretically Interesting Molecules; Thummel, R. P., Ed.; JAI Press: Greenwich, 1995; Vol. 3, pp 1-36. (b) Rabideau, P. W.; Sygula, A. Acc. Chem. Res. 1996, 29, 235-242. (c) Scott, L. T. Pure Appl. Chem. 1996, 68, 291-300. (d) Mehta, G.; Rao, H. S. P. Adv. Strain Org. Chem. 1997, 6, 139-187. (e) Mehta, G.; Rao, H. S. P. Tetrahedron 1998, 54, 13325-13370. (f) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Atual. Fis.-Quim. Org. 1999, 11, 138-150. (g) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Pure Appl. Chem. 1999, 71, 209-219.
9. Several reviews have already been published: (a) Rabideau, P. W.; Sygula, A. In Advances in Theoretically Interesting Molecules; Thummel, R. P., Ed.; JAI Press: Greenwich, 1995; Vol. 3, pp 1-36. (b) Rabideau, P. W.; Sygula, A. Acc. Chem. Res. 1996, 29, 235-242. (c) Scott, L. T. Pure Appl. Chem. 1996, 68, 291-300. (d) Mehta, G.; Rao, H. S. P. Adv. Strain Org. Chem. 1997, 6, 139-187. (e) Mehta, G.; Rao, H. S. P. Tetrahedron 1998, 54, 13325-13370. (f) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Atual. Fis.-Quim. Org. 1999, 11, 138-150. (g) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Pure Appl. Chem. 1999, 71, 209-219.
10. Several reviews have already been published: (a) Rabideau, P. W.; Sygula, A. In Advances in Theoretically Interesting Molecules; Thummel, R. P., Ed.; JAI Press: Greenwich, 1995; Vol. 3, pp 1-36. (b) Rabideau, P. W.; Sygula, A. Acc. Chem. Res. 1996, 29, 235-242. (c) Scott, L. T. Pure Appl. Chem. 1996, 68, 291-300. (d) Mehta, G.; Rao, H. S. P. Adv. Strain Org. Chem. 1997, 6, 139-187. (e) Mehta, G.; Rao, H. S. P. Tetrahedron 1998, 54, 13325-13370. (f) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Atual. Fis.-Quim. Org. 1999, 11, 138-150. (g) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Pure Appl. Chem. 1999, 71, 209-219.
11. Several reviews have already been published: (a) Rabideau, P. W.; Sygula, A. In Advances in Theoretically Interesting Molecules; Thummel, R. P., Ed.; JAI Press: Greenwich, 1995; Vol. 3, pp 1-36. (b) Rabideau, P. W.; Sygula, A. Acc. Chem. Res. 1996, 29, 235-242. (c) Scott, L. T. Pure Appl. Chem. 1996, 68, 291-300. (d) Mehta, G.; Rao, H. S. P. Adv. Strain Org. Chem. 1997, 6, 139-187. (e) Mehta, G.; Rao, H. S. P. Tetrahedron 1998, 54, 13325-13370. (f) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Atual. Fis.-Quim. Org. 1999, 11, 138-150. (g) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Pure Appl. Chem. 1999, 71, 209-219.
12. Several reviews have already been published: (a) Rabideau, P. W.; Sygula, A. In Advances in Theoretically Interesting Molecules; Thummel, R. P., Ed.; JAI Press: Greenwich, 1995; Vol. 3, pp 1-36. (b) Rabideau, P. W.; Sygula, A. Acc. Chem. Res. 1996, 29, 235-242. (c) Scott, L. T. Pure Appl. Chem. 1996, 68, 291-300. (d) Mehta, G.; Rao, H. S. P. Adv. Strain Org. Chem. 1997, 6, 139-187. (e) Mehta, G.; Rao, H. S. P. Tetrahedron 1998, 54, 13325-13370. (f) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Atual. Fis.-Quim. Org. 1999, 11, 138-150. (g) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Pure Appl. Chem. 1999, 71, 209-219.
13. Several reviews have already been published: (a) Rabideau, P. W.; Sygula, A. In Advances in Theoretically Interesting Molecules; Thummel, R. P., Ed.; JAI Press: Greenwich, 1995; Vol. 3, pp 1-36. (b) Rabideau, P. W.; Sygula, A. Acc. Chem. Res. 1996, 29, 235-242. (c) Scott, L. T. Pure Appl. Chem. 1996, 68, 291-300. (d) Mehta, G.; Rao, H. S. P. Adv. Strain Org. Chem. 1997, 6, 139-187. (e) Mehta, G.; Rao, H. S. P. Tetrahedron 1998, 54, 13325-13370. (f) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Atual. Fis.-Quim. Org. 1999, 11, 138-150. (g) Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.; Hagen, S. Pure Appl. Chem. 1999, 71, 209-219.
14. Such compounds have sometimes been referred to as "fullerene fragments" or "buckybowls".
15. For recent reviews of the fullerene field, see: (a) Hirsch, A. Fullerenes and Related Structures; Springer-Verlag: Berlin/Heidelberg, 1999. (b) Taylor, R. Lecture Notes on Fullerene Chemistry: A Handbook for Chemists; Imperial College Press: London, 1999.
16. For recent reviews of the fullerene field, see: (a) Hirsch, A. Fullerenes and Related Structures; Springer-Verlag: Berlin/Heidelberg, 1999. (b) Taylor, R. Lecture Notes on Fullerene Chemistry: A Handbook for Chemists; Imperial College Press: London, 1999.
17. Scott, L. T.; Bratcher, M. S.; Hagen, S. J. Am. Chem. Soc. 1996, 118, 8743-8744.
18. Clar, E. Polycyclic Hydrocarbons; Academic Press: New York, 1964; Vol. 1, pp 9-10.
19. (a) Katz, T. J.; Slusarek, W. J. Am. Chem. Soc. 1980, 102, 1058-1063.
20. (b) Helvenston, M. C.; Lynch, T. J. J. Organomet. Chem. 1989, 359, C50-C52. See also Chem. Abstr. registry no. 73255-13-7.
21. (b) Helvenston, M. C.; Lynch, T. J. J. Organomet. Chem. 1989, 359, C50-C52. See also Chem. Abstr. registry no. 73255-13-7.
22. (a) Hagen, S.; Nuechter, U.; Nuechter, M.; Zimmermann, G. Tetrahedron Lett. 1994, 35, 7013-7014.
23. (b) Hagen, S.; Nuechter, U.; Nuechter, M.; Zimmermann, G. Polycyclic Aromat. Compd. 1995, 4, 209-217.
24. (c) Hagen, S.; Christoph, H.; Zimmermann, G. Tetrahedron 1995, 51, 6961-6970.
25. (a) Bratcher, M. S.; Scott, L. T. Abstracts of Papers, 207th National Meeting of the American Chemical Society, San Diego, CA; American Chemical Society: Washington, DC, March 1994; Abstract ORGN 420.
26. (b) Scott, L. T.; Bratcher, M. S. Eighth International Symposium on Novel Aromatic Compounds, Braunschweig, Germany, July 30 to Aug 4, 1995; Abstract 7.
27. (c) Bratcher, M. S. Ph.D. Dissertation, Boston College, 1996.
28. (d) Bronstein, H. E. Ph.D. Dissertation, Boston College, Chestnut Hill, 1999.
29. See also: (a) Plater, M. J. Tetrahedron Lett. 1994, 35, 801-802. (b) Plater, M. J. Tetrahedron Lett. 1994, 35, 6147-6150.
30. See also: (a) Plater, M. J. Tetrahedron Lett. 1994, 35, 801-802. (b) Plater, M. J. Tetrahedron Lett. 1994, 35, 6147-6150.
31. (a) Hagen, S.; Bratcher, M. S.; Erickson, M. S.; Zimmermann, G.; Scott, L. T. Angew. Chem., Int. Ed. Engl. 1997, 36, 406-408.
32. (b) Brooks, M. A.; Scott, L. T. J. Am. Chem. Soc. 1999, 121, 5444-5449.
33. For other recent attempts to prepare substituted decacyclenes as potential precursors to 1, see: (a) Zimmermann, K.; Goddard, R.; Krueger, C.; Haenel, M. W. Tetrahedron Lett. 1996, 37, 8371-8374. (b) Zimmermann, K.; Haenel, M. W. Synlett 1997, 609-611.
34. For other recent attempts to prepare substituted decacyclenes as potential precursors to 1, see: (a) Zimmermann, K.; Goddard, R.; Krueger, C.; Haenel, M. W. Tetrahedron Lett. 1996, 37, 8371-8374. (b) Zimmermann, K.; Haenel, M. W. Synlett 1997, 609-611.
35. (a) Rehländer, P. Ph.D. Dissertation, University of Berlin, Germany, 1883.
36. (b) Rehländer, P. Chem. Ber. 1903, 36, 1583-1587.
37. (a) Moszew, J.; Zankowska-Jasinska, W. Rocz. Chem. 1958, 32, 225, 230 (Chem. Abstr. 1958, 52, 16316h).
38. (a) Moszew, J.; Zankowska-Jasinska, W. Rocz. Chem. 1958, 32, 225, 230 (Chem. Abstr. 1958, 52, 16316h).
39. (b) Staab, H. A.; Ipaktschi, J.; Nissen, A. Chem. Ber. 1971, 104, 1182-1190.
40. (c) Nakayama, J.; Segiri, T.; Oya, R.; Hoshino, M. J. Chem. Soc., Chem. Commun. 1980, 791-2.
41. (d) Chapman, O. L.; Gano, J.; West, P. R.; Regitz, M.; Maas, G. J. Am. Chem. Soc. 1981, 103, 7033-7036.
42. (e) Nakayama, J.; Ohshima, E.; Ishii, A.; Hoshino, M. J. Org. Chem. 1983, 48, 60-65.
43. (f) Do, Q. T.; Elothmani, D.; Simonet, J.; Le Guillanton, G. Bull. Soc. Chim. Fr. 1994, 131, 789-793.
44. For recent examples of such regiorandom trimerizations, see: (a) Reference 13a. (b) Sarobe, M. Ph.D. Dissertation, University of Utrecht, The Netherlands, 1998; Chapter 8. (c) Sarobe, M.; Fokkens, R. H.; Cleij, T. J.; Jenneskens, L. W.; Nibbering, N. M. M.; Stas, W.; Versluis, C. Chem. Phys. Lett. 1999, 313, 31.
45. For recent examples of such regiorandom trimerizations, see: (a) Reference 13a. (b) Sarobe, M. Ph.D. Dissertation, University of Utrecht, The Netherlands, 1998; Chapter 8. (c) Sarobe, M.; Fokkens, R. H.; Cleij, T. J.; Jenneskens, L. W.; Nibbering, N. M. M.; Stas, W.; Versluis, C. Chem. Phys. Lett. 1999, 313, 31.
46. For recent examples of such regiorandom trimerizations, see: (a) Reference 13a. (b) Sarobe, M. Ph.D. Dissertation, University of Utrecht, The Netherlands, 1998; Chapter 8. (c) Sarobe, M.; Fokkens, R. H.; Cleij, T. J.; Jenneskens, L. W.; Nibbering, N. M. M.; Stas, W.; Versluis, C. Chem. Phys. Lett. 1999, 313, 31.
47. (a) Elmorsy, S. S.; Pelter, A.; Smith, K. Tetrahedron Lett. 1991, 32, 4175-4176.
48. (b) Pyrko, A. N. Zh. Org. Khim. 1992, 28, 215-216.
49. (c) Plater, M. J. Synlett 1993, 405-406.
50. (d) Dehmlow, E. V.; Kelle, T. Synth. Commun. 1997, 27, 2021-2031.
51. (a) Elmorsy, S. S.; Pelter, A.; Smith, K.; Hursthouse, M. B.; Ando, D. Tetrahedron Lett. 1992, 33, 821-824.
52. (b) Elmorsy, S. S.; Khalil, A. G. M.; Girges, M. M.; Salama, T. A. Tetrahedron Lett. 1997, 38, 1071-1074.
53. 6 calculated at the pBP/DN**//AM1 level of theory).
54. Minimum energy molecular geometries were optimized at the AMI level of theory, and single point energies were calculated at the pBP/DN** level of theory using the computational chemistry programs implemented in Spartan 5.0 (Wavefunction, Inc., Irvine, CA 92612).
55. Both AMI calculations and simple resonance theory predict preferential attack at positions 1 and 8. The partial rate factors for protiodetritiation of 2-chloronaphthalene (experimental values) are also greatest at positions 1 and 8 (ref 23, p 106).
56. Taylor, R. Electrophilic Aromatic Substitution; Wiley: New York, 1990; Section 6.7.3.
57. Chloromethylation of 10 likewise gave almost exclusively the two products of monosubstitution at positions 1 and 8; however, the isomer ratio was closer to 1:1, and the two products could not be separated easily. Treatment of the mixture of chloromethyl compounds with KCN and cyclization of the corresponding carboxylic acids gave a mixture of the two acenaphthenones 8b and 9b in good overall yield, but no separation of isomers could be achieved at any intermediate stage in the synthesis. By tedious chromatography, it is possible to effect the separation of 8b and 9b on a small scale; however, this route was never developed into a practical synthesis.
58. Friedel-Crafts acetylation of 2-bromonaphthalene likewise gave almost exclusively the two products of monosubstitution at positions 1 and 8; however, the site selectivitiy was lower than with 2-chloronaphthalene.
59. Taylor, E. C.; Chiang, C.-S.; McKillop, A.; White, J. F. J. Am. Chem. Soc. 1976, 98, 6750-6752.
60. The only prior preparation of 8-chloro-1 (2H)-acenaphthylenone (8b) also entailed cyclization of (7-chloronaphthalen-1-y1)acetic acid (13); however, the published synthesis of 13 was considered too impractical for our purposes: (a) Price, C. C.; Voong, S. T. J. Org. Chem. 1949, 14, 111-115. (b) Karishin, A. P.; Mikhailenko, P. I.; Magda, V. I.; Lykho, V. P. Vestn. Khar'k. Politekh. Inst. 1975, 104, 52-56 (From: Ref. Zh., Khim. 1975, Abstr. No. 17ZH219; Chem. Abstr. 1976, 84, 121534).
61. The only prior preparation of 8-chloro-1 (2H)-acenaphthylenone (8b) also entailed cyclization of (7-chloronaphthalen-1-y1)acetic acid (13); however, the published synthesis of 13 was considered too impractical for our purposes: (a) Price, C. C.; Voong, S. T. J. Org. Chem. 1949, 14, 111- 115. (b) Karishin, A. P.; Mikhailenko, P. I.; Magda, V. I.; Lykho, V. P. Vestn. Khar'k. Politekh. Inst. 1975, 104, 52-56 (From: Ref. Zh., Khim. 1975, Abstr. No. 17ZH219; Chem. Abstr. 1976, 84, 121534).
62. The only prior preparation of 8-chloro-1 (2H)-acenaphthylenone (8b) also entailed cyclization of (7-chloronaphthalen-1-y1)acetic acid (13); however, the published synthesis of 13 was considered too impractical for our purposes: (a) Price, C. C.; Voong, S. T. J. Org. Chem. 1949, 14, 111- 115. (b) Karishin, A. P.; Mikhailenko, P. I.; Magda, V. I.; Lykho, V. P. Vestn. Khar'k. Politekh. Inst. 1975, 104, 52-56 (From: Ref. Zh., Khim. 1975, Abstr. No. 17ZH219; Chem. Abstr. 1976, 84, 121534).
63. The only prior preparation of 8-chloro-1 (2H)-acenaphthylenone (8b) also entailed cyclization of (7-chloronaphthalen-1-y1)acetic acid (13); however, the published synthesis of 13 was considered too impractical for our purposes: (a) Price, C. C.; Voong, S. T. J. Org. Chem. 1949, 14, 111- 115. (b) Karishin, A. P.; Mikhailenko, P. I.; Magda, V. I.; Lykho, V. P. Vestn. Khar'k. Politekh. Inst. 1975, 104, 52-56 (From: Ref. Zh., Khim. 1975, Abstr. No. 17ZH219; Chem. Abstr. 1976, 84, 121534).
64. Mass spectroscopic analysis of the byproducts formed in the trimerizations carried out at 180°C in 1,2-dichlorobenzene reveals the presence of what appears to be a cyclic tetramer, the next higher homologue of trichlorodecacyclene 5 (X = Cl).
65. 3): δ 8.38 (d, J = 6.8 Hz, 1H), 8.18 (d, J = 8.4 Hz, 1H), 7.84 (d, J = 8.4 Hz, 1H), 7.77 (d, J = 8.8 Hz, 1H), 7.72 (dd, J = 8.0, 7.2 Hz, 1H), 7.71 (d, J = 8.4 Hz, 1H), 7.63 (d, J = 8.4 Hz, 1H), 7.35 (dd, J = 8.4, 7.2 Hz, 1H), 7.20 (d, J = 8.8 Hz, 1H), 7.15 (d, J = 7.6 Hz, 1H), 5.65 (s, 1H), 2.75 (s, 1H).
66. 3h" polycyclic aromatic compounds, see: Barnett, L.; Ho, D. M.; Baldridge, K. K.; Pascal, R. A., Jr. J. Am. Chem. Soc. 1999, 121, 727-733.
67. X-ray structure of 2: Ho, D. M.; Pascal, R. A., Jr. Chem. Mater. 1993, 5, 1358-1361. The experimentally determined dihedral angles in the bottoms of the fjord regions (C3a-C3b-C3c-C3d) for decacyclene (2) and 3,9,15-trichlorodecacyclene (5b) are 9.10° and 13.34°, respectively. AM1 geometry optimizations predict 8.50° and 13.14°, respectively.
68. Forkey, D. M.; Attar, S.; Noll, B. C.; Koerner, R.; Olmstead, M. M.; Balch, A. L. J. Am. Chem. Soc. 1997, 119, 5766-5767.
69. 32
70. (a) Haddon, R. C.; Scott, L. T. Pure Appl. Chem. 1986, 58, 137-142.
71. (b) Haddon, R. C. J. Am. Chem. Soc. 1990, 112, 3385-3389.
72. (c) Haddon, R. C. J. Am. Chem. Soc. 1997, 119, 1797-1798.
73. 12) at 8.9 ppm.
74. Schulman, J. M.; Disch, R. L. J. Comput. Chem. 1998, 19, 189-194.
75. (a) McMahon, B. J. B.S. Thesis, Boston College, 1996.
76. (b) Scott, L. T.; Hagen, S. Unpublished observations.
77. For an alternative approach to 16a, see: De Frutos, O.; Gomez-Lor, B.; Granier, T.; Monge, M. A.; Gutierrez-Puebla, E.; Echavarren, A. M. Angew. Chem., Int. Ed. 1999, 38, 204-207.
78. Scott, L. T.; Boorum, M. M. Unpublished results.
79. 16b,c (d) Gomez-Lor, B.; de Frutos, O.; Echavarren, A. M. Chem. Commun. 1999, 2431-2432.
80. 16b,c (d) Gomez-Lor, B.; de Frutos, O.; Echavarren, A. M. Chem. Commun. 1999, 2431-2432.
81. 16b,c (d) Gomez-Lor, B.; de Frutos, O.; Echavarren, A. M. Chem. Commun. 1999, 2431-2432.
82. 16b,c (d) Gomez-Lor, B.; de Frutos, O.; Echavarren, A. M. Chem. Commun. 1999, 2431-2432.
83. 13C NMR signals.