Tandem [4 + 2]/[3 + 2] cycloadditions of nitroalkenes. 11. The synthesis of (+)-crotanecine

Journal of the American Chemical Society

Volumn 119, Issue 1, 1997, Pages 125-137

  Denmark, Scott E ^a   Thorarensen, Atli ^a  

^a UNIVERSITY OF ILLINOIS AT URBANA CHAMPAIGN   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CROTANECINE; PYRROLIZIDINE ALKALOID; UNCLASSIFIED DRUG;

ARTICLE; DRUG SYNTHESIS; ENANTIOMER; IN VITRO STUDY; NUCLEAR MAGNETIC RESONANCE; REACTION ANALYSIS; STEREOCHEMISTRY; TECHNIQUE;

EID: 0031049707     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja963084d     Document Type: Article

References (136)

1. Hall, N. Science 1994, 266, 32.
2. (a) Tietze, L. F.; Beifuss, U. Angew. Chem., Int. Ed. Engl. 1993, 32, 131.
3. (b) Tietze, L. F.; Bachmann, J.; Wichmann, J.; Burkhardt, O. Synthesis 1994, 1185.
4. (c) Bunce, R. A. Tetrahedron 1995, 51, 13103.
5. (d) Tietze, L. F. Chem. Rev. 1996, 96, 115.
6. (e) Winkler, J. D. Chem. Rev. 1996, 96, 167.
7. (f) Ryu, I.; Sonoda, N.; Curran, D. P. Chem. Rev. 1996, 96, 177.
8. (g) Parsons, P. J.; Penkett, C. S.; Shell, A. J. Chem. Rev. 1996, 96, 195.
9. (h) Wang, K. K. Chem. Rev. 1996, 96, 207.
10. (i) Padwa, A.; Weingarten, M. D. Chem. Rev. 1996, 96, 223.
11. (a) Ho, T.-L. Tandem Organic Reactions; Wiley: New York, 1992.
12. (b) Thebtaranonth, C.; Thebtaranonth, Y. Cyclization Reactions; CRC Press: Boca Raton, FL, 1994.
13. Denmark, S. E.; Thorarensen, A. Chem. Rev. 1996, 96, 137.
14. Denmark, S, E.; Thorarensen, A. J. Org. Chem. 1994, 59, 5672.
15. Denmark, S. E.; Thorarensen, A.; Middleton, D. S. J. Org. Chem. 1995, 60, 3574.
16. Atal, C. K.; Kapur, K. K.; Culvenor, C. C. J.; Smith, L. W. Tetrahedron Lett. 1966, 537.
17. (a) Culvenor, C. C. J.; Smith, L. W.; Willing, R. I. Chem. Commun. 1970, 65. Anacrotine has in addition been isolated from C. laburnifolia:
18. (b) Sawhney, R. S.; Girotra, R. N.; Atal, C. K.; Culvenor, C. C. J.; Smith, L. W. Indian J. Chem. 1967, 5, 655.
19. (c) Crout, D. H. G. J. Chem. Soc., Perkin Trans. 1 1972, 1602.
20. This report contains the only reported physical data of analytically pure crotanecine: Mattocks, A. R. J. Chem. Soc. C 1968, 235.
21. Culvenor, C. C. J.; Smith, L. W. Anal. Quim. 1972, 68, 883.
22. Mackay, M, F.; Sadek, M.; Culvenor, C. C. J. Acta Crystallogr. C 1984, 40, 1073.
23. Richardson, J. F.; Culvenor, C. C. J. Acta Crystallogr. C 1985, 41, 1475.
24. Röder, E.; Liu, K.; Bourauel, T. Fresenius' J. Anal. Chem. 1992, 342, 719.
25. (a) Mattocks, A. R.; Driver, H. E. Chem.-Biol. Interact. 1987, 63, 91.
26. (b) Mattocks, A. R.; Bird, I. Chem.-Biol. Interact. 1983, 43, 209.
27. (c) Mattocks, A. R.; Jukes, R. Nat. Toxins 1992, 1, 89.
28. Yadav, V. K.; Rüeger, H.; Benn, M. Heterocycles 1984, 22, 2735.
29. Bennett, R. B. III: Cha, J. K. Tetrahedron Lett. 1990, 31, 5437.
30. Buchanan, J. G.; Jigajinni, V. B.; Singh, G.; Wightman, R. H. J. Chem. Soc., Perkin Trans. 1 1987, 2377.
31. For recent reviews on the synthesis and the biological properties of pyrrolizidines see: (a) Natural Occuring Pyrrolizidine Alkaloids; Rizk, A.-F. M., Ed.; CRC: Boston, MA, 1991.
32. (b) Pyrrolizidine Alkaloids; World Health Organization: Geneva, 1988.
33. (c) Mattocks, A. R. Chemistry and Toxicology of Pyrrolizidine Alkaloids; Academic Press: New York, 1986.
34. (d) Robins, D. J. Nat. Prod. Rep. 1995, 12, 413.
35. (e) Ikeda, M.; Sato, T.; Ishibashi, H. Heterocycles 1988, 27, 1465.
36. (f) Dai, W.-M.; Nagao, Y. Heterocycles 1990, 30, 1231.
37. (g) Wróbel, J. T. The Alkaloids: Brossi, A., Ed.; Academic Press: New York, 1985; Vol. 26, Chapter 7.
38. Denmark, S. E.; Schnute, M. E. J. Org. Chem. 1994, 59, 4576.
39. Schnute, M. E. Personal communication.
40. (a) Fleming, I.; Henning, R.; Plaut, H. J. Chem. Soc., Chem. Commun. 1984, 29.
41. (b) Chow, H.-F.; Fleming, I. Tetrahedron Lett. 1985, 29, 397.
42. (c) Fleming, I.; Hill, J. H. M.; Parker, D.; Waterson, D. J. Chem. Soc., Chem. Commun. 1985, 318.
43. (a) Tamao, K.; Ishida, N. J. Organomet. Chem. 1984, 269, C37.
44. (b) Tamao, K.; Ishida, N.; Tanaka, T.; Kumada, M. Organometallics 1983, 2, 1694.
45. (c) Tamao, K.; Kumada, M.; Maeda, K. Tetrahedron Lett. 1984, 25, 321.
46. For reviews oxidation of C-Si bonds, see: (a) Colvin, E. W. In Comprehensive Organic Synthesis: Ley, S. V., Ed.; Pergamon Press: Oxford, U.K., 1991; Vol. 7, Chapter 4.3. (b) Fleming, I. Chemtracts: Org. Chem. 1996, 9, 1.
47. For reviews oxidation of C-Si bonds, see: (a) Colvin, E. W. In Comprehensive Organic Synthesis: Ley, S. V., Ed.; Pergamon Press: Oxford, U.K., 1991; Vol. 7, Chapter 4.3. (b) Fleming, I. Chemtracts: Org. Chem. 1996, 9, 1.
48. For recent reviews concerning the use of silicon building blocks in organic synthesis, see: (a) White, J. M. Aust. J. Chem. 1995, 48, 1227. (b) Hwu, J. R.; Patel, H. V. Synlett 1995, 989. (c) Luh, T.-Y.; Wong, K.-T. Synthesis 1993, 349.
49. For recent reviews concerning the use of silicon building blocks in organic synthesis, see: (a) White, J. M. Aust. J. Chem. 1995, 48, 1227. (b) Hwu, J. R.; Patel, H. V. Synlett 1995, 989. (c) Luh, T.-Y.; Wong, K.-T. Synthesis 1993, 349.
50. For recent reviews concerning the use of silicon building blocks in organic synthesis, see: (a) White, J. M. Aust. J. Chem. 1995, 48, 1227. (b) Hwu, J. R.; Patel, H. V. Synlett 1995, 989. (c) Luh, T.-Y.; Wong, K.-T. Synthesis 1993, 349.
51. (a) Taber, D. F.; Bhamidipati, R. S.; Yet, L. J. Org. Chem. 1995, 60, 5537.
52. (b) Kolb, H. C.; Ley, S. V.; Slawin, A. M. Z.; Williams, D. J. J. Chem. Soc., Perkin Trans. 1 1992, 2735.
53. (c) Sieburth, S. M.; Fensterbank, L. J. Org. Chem. 1992, 57, 5279.
54. (d) Stork, G.; Chan, T. Y.; Breault, G. A. J. Am. Chem. Soc. 1992, 114, 7578.
55. (e) Tamao, K.; Kobayashi, K.; Ito, Y. J. Am. Chem. Soc. 1989, 111, 6478.
56. (f) Chen, R.-M.; Weng, W.-W.; Luh, T.-Y. J. Org. Chem. 1995, 60, 3272.
57. (g) Shea, K. J.; Zandi, K. S.; Staab, A. J.; Carr, R. Tetrahedron Lett. 1990, 31, 5885.
58. (h) Singleton, D. A.; Redman, A. M. Tetrahedron Lett. 1994, 35, 509.
59. (i) Koreeda, M.; Teng, K.; Murata, T. Tetrahedron Lett. 1990, 31, 5997.
60. Fleming, I. Chem. Soc. Rev. 1981, 10, 83.
61. (a) Moyano, A.; Charbonnier, F.; Greene, A. E. J. Org. Chem. 1987, 52, 2919.
62. (b) Charbonnier, F.; Moyano, A.; Greene, A. E. J. Org. Chem. 1987, 52, 2303.
63. (a) Denmark, S. E.; Senanayake, C. B. W. J. Org. Chem. 1993, 58, 1853.
64. (b) Denmark, S. E.; Schnute, M. E.; Senanayake, C. B. W. J. Org. Chem. 1993, 58, 1859.
65. (c) Denmark, S. E.; Marcin, L. R. J. Org. Chem. 1995, 60, 3221.
66. Porter, N. A.; Dussault, P.; Breyer, R. A.; Kaplan, J.; Morelli, J. Chem. Res. Toxicol. 1990, 3, 236.
67. Solá, L.; Castro, J.; Moyano, A.; Pericás, M. A.; Riera, A. Tetrahedron Lett. 1992, 33, 2863. For reductions of propynyl ethers to E-propenyl ethers, see also ref 28.
68. For aluminum-based reductions of propargyl compound to E-alkenes, see: (a) Corey, E. J.; Kirst, H. A.; Katzenellenbogen, J. A. J. Am. Chem. Soc. 1970, 92, 6314. (b) Zweifel, G.; Lewis, W.; On, H. P. J. Am. Chem. Soc. 1979, 101, 5101. (c) Denmark, S. E.; Jones, T. K. J. Org. Chem. 1982, 47, 4595. (d) Marshall, J. A.; Shearer, B. G.; Crooks, S. L. J. Org. Chem. 1987, 52, 1236. (e) Kang, M. J.; Jang, J.-S.; Lee, S.-G. Tetrahedron Lett. 1995, 36, 8829. (f) Zweifel, G.; Steele, R. B. J. Am. Chem. Soc. 1967, 89, 5085.
69. For aluminum-based reductions of propargyl compound to E-alkenes, see: (a) Corey, E. J.; Kirst, H. A.; Katzenellenbogen, J. A. J. Am. Chem. Soc. 1970, 92, 6314. (b) Zweifel, G.; Lewis, W.; On, H. P. J. Am. Chem. Soc. 1979, 101, 5101. (c) Denmark, S. E.; Jones, T. K. J. Org. Chem. 1982, 47, 4595. (d) Marshall, J. A.; Shearer, B. G.; Crooks, S. L. J. Org. Chem. 1987, 52, 1236. (e) Kang, M. J.; Jang, J.-S.; Lee, S.-G. Tetrahedron Lett. 1995, 36, 8829. (f) Zweifel, G.; Steele, R. B. J. Am. Chem. Soc. 1967, 89, 5085.
70. For aluminum-based reductions of propargyl compound to E-alkenes, see: (a) Corey, E. J.; Kirst, H. A.; Katzenellenbogen, J. A. J. Am. Chem. Soc. 1970, 92, 6314. (b) Zweifel, G.; Lewis, W.; On, H. P. J. Am. Chem. Soc. 1979, 101, 5101. (c) Denmark, S. E.; Jones, T. K. J. Org. Chem. 1982, 47, 4595. (d) Marshall, J. A.; Shearer, B. G.; Crooks, S. L. J. Org. Chem. 1987, 52, 1236. (e) Kang, M. J.; Jang, J.-S.; Lee, S.-G. Tetrahedron Lett. 1995, 36, 8829. (f) Zweifel, G.; Steele, R. B. J. Am. Chem. Soc. 1967, 89, 5085.
71. For aluminum-based reductions of propargyl compound to E-alkenes, see: (a) Corey, E. J.; Kirst, H. A.; Katzenellenbogen, J. A. J. Am. Chem. Soc. 1970, 92, 6314. (b) Zweifel, G.; Lewis, W.; On, H. P. J. Am. Chem. Soc. 1979, 101, 5101. (c) Denmark, S. E.; Jones, T. K. J. Org. Chem. 1982, 47, 4595. (d) Marshall, J. A.; Shearer, B. G.; Crooks, S. L. J. Org. Chem. 1987, 52, 1236. (e) Kang, M. J.; Jang, J.-S.; Lee, S.-G. Tetrahedron Lett. 1995, 36, 8829. (f) Zweifel, G.; Steele, R. B. J. Am. Chem. Soc. 1967, 89, 5085.
72. For aluminum-based reductions of propargyl compound to E-alkenes, see: (a) Corey, E. J.; Kirst, H. A.; Katzenellenbogen, J. A. J. Am. Chem. Soc. 1970, 92, 6314. (b) Zweifel, G.; Lewis, W.; On, H. P. J. Am. Chem. Soc. 1979, 101, 5101. (c) Denmark, S. E.; Jones, T. K. J. Org. Chem. 1982, 47, 4595. (d) Marshall, J. A.; Shearer, B. G.; Crooks, S. L. J. Org. Chem. 1987, 52, 1236. (e) Kang, M. J.; Jang, J.-S.; Lee, S.-G. Tetrahedron Lett. 1995, 36, 8829. (f) Zweifel, G.; Steele, R. B. J. Am. Chem. Soc. 1967, 89, 5085.
73. For aluminum-based reductions of propargyl compound to E-alkenes, see: (a) Corey, E. J.; Kirst, H. A.; Katzenellenbogen, J. A. J. Am. Chem. Soc. 1970, 92, 6314. (b) Zweifel, G.; Lewis, W.; On, H. P. J. Am. Chem. Soc. 1979, 101, 5101. (c) Denmark, S. E.; Jones, T. K. J. Org. Chem. 1982, 47, 4595. (d) Marshall, J. A.; Shearer, B. G.; Crooks, S. L. J. Org. Chem. 1987, 52, 1236. (e) Kang, M. J.; Jang, J.-S.; Lee, S.-G. Tetrahedron Lett. 1995, 36, 8829. (f) Zweifel, G.; Steele, R. B. J. Am. Chem. Soc. 1967, 89, 5085.
74. For chromium-based reducing agents, see: (a) Castro, C. E.; Stephens, R. D. J. Am. Chem. Soc. 1964, 86, 4358. (b) Smith, A. B., III; Levenberg, P. A.; Suits, J. Z. Synthesis 1986, 184. (c) Constantino, M. G.; Donate, P. M.; Petragnani, N. J. Org. Chem. 1986, 51, 253.
75. For chromium-based reducing agents, see: (a) Castro, C. E.; Stephens, R. D. J. Am. Chem. Soc. 1964, 86, 4358. (b) Smith, A. B., III; Levenberg, P. A.; Suits, J. Z. Synthesis 1986, 184. (c) Constantino, M. G.; Donate, P. M.; Petragnani, N. J. Org. Chem. 1986, 51, 253.
76. For chromium-based reducing agents, see: (a) Castro, C. E.; Stephens, R. D. J. Am. Chem. Soc. 1964, 86, 4358. (b) Smith, A. B., III; Levenberg, P. A.; Suits, J. Z. Synthesis 1986, 184. (c) Constantino, M. G.; Donate, P. M.; Petragnani, N. J. Org. Chem. 1986, 51, 253.
77. 3, see: (a) Schwarz, M.; Waters, R. M. Synthesis 1972, 567. (b) Warthen, J. D., Jr.; Jacobson, M. Synthesis 1973, 616. (c) Boland, W.; Hansen, V.; Jaenicke, L. Synthesis 1979, 114.
78. 3, see: (a) Schwarz, M.; Waters, R. M. Synthesis 1972, 567. (b) Warthen, J. D., Jr.; Jacobson, M. Synthesis 1973, 616. (c) Boland, W.; Hansen, V.; Jaenicke, L. Synthesis 1979, 114.
79. 3, see: (a) Schwarz, M.; Waters, R. M. Synthesis 1972, 567. (b) Warthen, J. D., Jr.; Jacobson, M. Synthesis 1973, 616. (c) Boland, W.; Hansen, V.; Jaenicke, L. Synthesis 1979, 114.
80. For a review on the reduction of triple-bonded groups, see: Hutchins, R. O.; Hutchins, M. G. K. In The Chemistry of the Functional Groups, Supplement C; Patai, S., Rappoport, Z., Eds; John Wiley: New York, 1983; Chapter 14, p 571.
81. For the use of DIBAL-H for the preparation of either (E)-or (Z)-alkenes, see: (a) Zweifel, G.; On, H. P. Synthesis 1980, 803. (b) Eisch, J. J.; Foxton, M. W. J. Org. Chem. 1971, 36, 3520. (c) Granitzer, W.; Stütz, A. Tetrahedron Lett. 1979, 3145.
82. For the use of DIBAL-H for the preparation of either (E)-or (Z)-alkenes, see: (a) Zweifel, G.; On, H. P. Synthesis 1980, 803. (b) Eisch, J. J.; Foxton, M. W. J. Org. Chem. 1971, 36, 3520. (c) Granitzer, W.; Stütz, A. Tetrahedron Lett. 1979, 3145.
83. For the use of DIBAL-H for the preparation of either (E)-or (Z)-alkenes, see: (a) Zweifel, G.; On, H. P. Synthesis 1980, 803. (b) Eisch, J. J.; Foxton, M. W. J. Org. Chem. 1971, 36, 3520. (c) Granitzer, W.; Stütz, A. Tetrahedron Lett. 1979, 3145.
84. For reviews of carbocuparation, see: (a) Normant, J. F.; Alexakis, A. Synthesis 1981, 841. (b) Casson, S.; Kocienski, P. Contemp. Org. Synth. 1995, 2, 19.
85. For reviews of carbocuparation, see: (a) Normant, J. F.; Alexakis, A. Synthesis 1981, 841. (b) Casson, S.; Kocienski, P. Contemp. Org. Synth. 1995, 2, 19.
86. For recent reviews of cupration in organic synthesis, see: (a) Lipshutz, B. H.; Sengupta, S. Org. React. 1992, 41, 135. (b) Lipshutz, B. H. In Organometallics in Synthesis-A Manual; Schlosser, M., Ed.; John Wiley: New York, 1994; Chapter 4, p 283.
87. For recent reviews of cupration in organic synthesis, see: (a) Lipshutz, B. H.; Sengupta, S. Org. React. 1992, 41, 135. (b) Lipshutz, B. H. In Organometallics in Synthesis-A Manual; Schlosser, M., Ed.; John Wiley: New York, 1994; Chapter 4, p 283.
88. Fleming, I.; Newton, T. W.; Roessler, F. J. Chem. Soc., Perkin Trans. 1 1981, 2527.
89. (a) George, M. V.; Peterson, D. J.; Gilman, H. J. Am. Chem. Soc. 1960, 82, 403.
90. (b) Gilman, H.; Lichtenwalter, G. D. J. Am. Chem. Soc. 1958, 80, 608.
91. For a review of silyl anions, see: Tamao, K.; Kawachi, A. In Advances in Organometallic Chemistry; Stone, F. G. A., West, R., Eds.; Academic Press: New York, 1995; Vol. 38, Chapter 1, p 1.
92. Thorarensen, A.; Swiss, K. A.; Denmark, S. E. Acta Crystallogr. C 1996, 52, 2558.
93. Defined with respect to folding of the tether.
94. (a) Fleming, I.; Sanderson, P. E. J. Tetrahedron Lett. 1987, 28, 4229.
95. (b) Fleming, I.; Henning, R.; Parker, D. C.; Plaut, H. E.; Sanderson, P. E. J. J. Chem. Soc., Perkin Trans. 1 1995, 317.
96. (a) Niwa, H.; Kuroda, A.; Yamada, K. Chem. Lett. 1983, 125.
97. (b) Niwa, H.; Miyachi, Y.; Okamoto, O.; Uosaki, Y.; Yamada, K. Tetrahedron Lett. 1986, 27, 4605.
98. (c) Kano, S.; Yuasa, Y.; Shibuya, S. Heterocycles 1988, 27, 253.
99. (d) Robins, D. J.; Sakdarat, S. J. Chem. Soc., Perkin Trans. 1 1979, 1734.
100. (e) Robins, D. J.; Sakdarat, S. J. Chem. Soc., Perkin Trans. 1 1981, 909.
101. (f) Terao, Y.; Imai, N.; Achiwa, K.; Sekiya, M. Chem. Pharm. Bull. 1982, 30, 3167.
102. (g) Vedejs, E.; Martinez, G. R. J. Am. Chem. Soc. 1980, 102, 7993.
103. (h) Vedejs, E.; Larsen, S.; West, F. G. J. Org. Chem. 1985, 50, 2170.
104. (a) Liotta, D.; Markiewicz, W.; Santiesteban, H. Tetrahedron Lett. 1977, 4365.
105. (b) Liotta, D.; Santiesteban, H. Tetrahedron Lett. 1977, 4369.
106. (c) Tiecco, M.; Testaferri, L.; Tingoli, M.; Chianelli, D.; Montanucci, M. Synth. Commun. 1983, 13, 617.
107. (d) Reich, H. J.; Wollowitz, S.; Trend, J. E.; Chow, F.; Wendelborn, D. F. J. Org. Chem. 1978, 43, 1697.
108. (e) Liotta, D.; Sunay, U.; Santiesteban, H.; Markiewicz, W. J. Org. Chem. 1981, 46, 2605.
109. For review, see: (f) Clive, D. L. J. Tetrahedron 1978, 34, 1049.
110. (g) Monahan, R.; Brown, D.; Waykole, L.; Liotta, D. In Organoselenium Chemistry; Liotta, D., Ed.; John Wiley: New York, 1987; Chapter 4, p 207.
111. (a) Murray, A.; Proctor, G. R.; Murray, P. J. Tetrahedron Lett. 1995, 36, 291.
112. (b) Murray, A.; Proctor, G. R.; Murray, P. J. Tetrahedron 1996, 52, 3757.
113. (a) Sato, T.; Tsujimoto, K.; Matsubayashi, K.-I.; Ishibashi, H.; Ikeda, M. Chem. Pharm. Bull. 1992, 40, 2308.
114. (b) Ishibashi, H.; Ozeki, H.; Ikeda, M. J. Chem. Soc., Chem. Commun. 1986, 654.
115. Keck, G. E.; Cressman, E. N. K.; Enholm, E. J. J. Org. Chem. 1989, 54, 4345.
116. (a) Cabezas, N.; Thierry, J.; Potier, P. Heterocycles 1989, 28, 607. Other preparations of 47:
117. (b) Gramain, J.-C.; Remuson, R.; Vallée, D. J. Org. Chem. 1985, 50, 710.
118. (c) Pinnick, H. W.; Chang, Y.-H. J. Org. Chem. 1978, 43, 4662.
119. Casiraghi, G.; Spanu, P.; Rassu, G.; Pinna, L.; Ulgheri, F. J. Org. Chem. 1994, 59, 2906.
120. The resistance of the methyl acetal to hydrolysis was most likely due to the inductive effect of the additional hydroxyl group at C(5). The inductive effect disfavors the formation of the intermediate oxocarbenium ion, which is a necessary intermediate in the hydrolysis.
121. (a) Brown, H. C.; Heim, P.; Yoon, N. M. J. Am. Chem. Soc. 1970, 92, 1637.
122. (b) Brown, H. C.; Heim, P. J. Org. Chem. 1973, 38, 912.
123. (c) Brown, H. C.; Choi, Y. M.; Narasimhan, S. J. Org. Chem. 1982, 47, 3153.
124. Pretsch, E.; Seibl, J.; Clere, T.; Simon, W. Tables of Spectral Data for Structure Determination of Organic Compounds, 2nd ed.; Springer-Verlag: New York, 1989; p 1260.
125. 7 (55) Similar observation have been made by Dr. Russell J. Molyneux (U.S. Department of Agriculture, Albany, CA) (private communications).
126. (a) Sharma, S.; Oehlschlager, A. C. Tetrahedron 1989, 45, 557.
127. (b) Sharma, S.; Oehlschlager, A. C. J. Org. Chem. 1989, 54, 5383.
128. (a) Cuadrado, P.; González, A. M.; Pulido, F. J.; Fleming, I. Tetrahedron Lett. 1988, 29, 1825.
129. (b) Barbero, A.; Cuadrado, P.; González, A. M.; Pulido, F. J.; Fleming, I. J. Chem. Soc., Perkin Trans 1 1991, 2811.
130. Cabezas, J. A.; Oehlschlager, A. C. Synthesis 1994, 432.
131. Denmark, S. E.; Moon, Y.-C.; Cramer, C. J.; Dappen, M. S.; Senanayake, C. B. W. Tetrahedron 1990, 46, 7373.
132. Denmark, S. E.; Schnute, M. E.; Marcin, L. R.; Thorarensen, A. J. Org. Chem. 1995, 60, 3205.
133. The si and re faces of the vinyl ether are defined with respect to the oxygen.
134. The si and re faces of the nitroalkene are defined with respect to the nitrogen.
135. An intermediate resulting from the cleavage of the five-membered ring has been observed for nitroso acetal derived from the tandem inter[4 + 2]/inter[3 + 2] cycloaddition sequence employing nickel-aluminum alloy/sodium hydroxide. Schnute, M. E. Ph.D. Thesis, University of Illinois, Urbana, 1995, p 139.
136. Denmark, S. E.; Moon, Y.-C.; Senanayake, C. B. W. J. Am. Chem. Soc. 1990, 112, 311.