Regio- and Stereocontrolled Conjugate Radical Addition to a Desymmetrized Fumarate Derivative: An Efficient Synthesis of (-)-Nephrosteranic Acid and (-)-Roccellaric Acid

Angewandte Chemie (International Edition in English)

Volumn 36, Issue 3, 1997, Pages 274-276

  Sibi, Mukund P ^a   Ji, Jianguo ^a  

^a NORTH DAKOTA STATE UNIVERSITY   (United States)

Author keywords

C C coupling; Lactones; Lewis acids; Radicals

Indexed keywords

EID: 0030903174     PISSN: 05700833     EISSN: None     Source Type: Journal    
DOI: 10.1002/anie.199702741     Document Type: Article

References (44)

1. C. P. Decicco, D. J. Nelson, R. L. Corbett, J. C. Dreabit, J. Org. Chem. 1995, 60, 4782, and references therein.
2. a) M. P. Sibi, C. P. Jasperse, J. Ji, J. Am. Chem. Soc. 1995, 117, 10779;
3. b) M. P. Sibi, J. Ji, Angew. Chem. 1996, 108, 198; Angew. Chem. Int. Ed. Engl. 1996, 35, 190.
4. b) M. P. Sibi, J. Ji, Angew. Chem. 1996, 108, 198; Angew. Chem. Int. Ed. Engl. 1996, 35, 190.
5. c) For discussions on diastereoselectivity in radical reactions with acyclic substrates see: D. P. Curran, N. A. Porter, B. Giese, Stereochemistry of Radical Reactions, VCH, Weinheim, 1995; B. Giese, Radicals in Organic Synthesis. Formation of Carbon-Carbon Bonds, Pergamon, Oxford, 1986; N. A. Porter, B. Giese, D. P. Curran, Acc. Chem. Res. 1991, 24, 296; W. Smadja, Synlett 1994, 1; B. Giese, Angew. Chem. 1989, 101, 993; Angew. Chem. Int. Ed. Engl. 1989, 28, 969.
6. c) For discussions on diastereoselectivity in radical reactions with acyclic substrates see: D. P. Curran, N. A. Porter, B. Giese, Stereochemistry of Radical Reactions, VCH, Weinheim, 1995; B. Giese, Radicals in Organic Synthesis. Formation of Carbon-Carbon Bonds, Pergamon, Oxford, 1986; N. A. Porter, B. Giese, D. P. Curran, Acc. Chem. Res. 1991, 24, 296; W. Smadja, Synlett 1994, 1; B. Giese, Angew. Chem. 1989, 101, 993; Angew. Chem. Int. Ed. Engl. 1989, 28, 969.
7. c) For discussions on diastereoselectivity in radical reactions with acyclic substrates see: D. P. Curran, N. A. Porter, B. Giese, Stereochemistry of Radical Reactions, VCH, Weinheim, 1995; B. Giese, Radicals in Organic Synthesis. Formation of Carbon-Carbon Bonds, Pergamon, Oxford, 1986; N. A. Porter, B. Giese, D. P. Curran, Acc. Chem. Res. 1991, 24, 296; W. Smadja, Synlett 1994, 1; B. Giese, Angew. Chem. 1989, 101, 993; Angew. Chem. Int. Ed. Engl. 1989, 28, 969.
8. c) For discussions on diastereoselectivity in radical reactions with acyclic substrates see: D. P. Curran, N. A. Porter, B. Giese, Stereochemistry of Radical Reactions, VCH, Weinheim, 1995; B. Giese, Radicals in Organic Synthesis. Formation of Carbon-Carbon Bonds, Pergamon, Oxford, 1986; N. A. Porter, B. Giese, D. P. Curran, Acc. Chem. Res. 1991, 24, 296; W. Smadja, Synlett 1994, 1; B. Giese, Angew. Chem. 1989, 101, 993; Angew. Chem. Int. Ed. Engl. 1989, 28, 969.
9. c) For discussions on diastereoselectivity in radical reactions with acyclic substrates see: D. P. Curran, N. A. Porter, B. Giese, Stereochemistry of Radical Reactions, VCH, Weinheim, 1995; B. Giese, Radicals in Organic Synthesis. Formation of Carbon-Carbon Bonds, Pergamon, Oxford, 1986; N. A. Porter, B. Giese, D. P. Curran, Acc. Chem. Res. 1991, 24, 296; W. Smadja, Synlett 1994, 1; B. Giese, Angew. Chem. 1989, 101, 993; Angew. Chem. Int. Ed. Engl. 1989, 28, 969.
10. c) For discussions on diastereoselectivity in radical reactions with acyclic substrates see: D. P. Curran, N. A. Porter, B. Giese, Stereochemistry of Radical Reactions, VCH, Weinheim, 1995; B. Giese, Radicals in Organic Synthesis. Formation of Carbon-Carbon Bonds, Pergamon, Oxford, 1986; N. A. Porter, B. Giese, D. P. Curran, Acc. Chem. Res. 1991, 24, 296; W. Smadja, Synlett 1994, 1; B. Giese, Angew. Chem. 1989, 101, 993; Angew. Chem. Int. Ed. Engl. 1989, 28, 969.
11. For work on radical additions to fumarates using imides derived from Kemp's triacid see: a) J. G. Stack, D. P. Curran, J. Rebek, Jr., P. Ballester, J. Am. Chem. Soc. 1991, 113, 5918; b) J. G. Stack, D. P. Curran, S. V. Geib, J. Rebek, Jr., P. Ballester, ibid. 1992, 114, 7007. For examinations of selectivity in radical additions to fumarates and related systems see: N. A. Porter, J. D. Bruhnke, W.-X. Wu, I. J. Rosenstein, R. A. Breyer, J. Am. Chem. Soc. 1992, 114, 7664; B. Giese, M. Zehnder, M. Roth, H.-G. Zeitz, ibid. 1990, 112, 6741; N. A. Porter, D. M. Scott, B. Lacher, B. Giese, H.-G. Zeitz, H. J. Lindner, ibid. 1989, 111, 8311; D. M. Scott, A. T. McPhail, N. A. Porter, Tetrahedron Lett. 1990, 31, 707; M. Bulliard, H.-G. Zeitz, B. Giese, Synlett 1991, 423.
12. For work on radical additions to fumarates using imides derived from Kemp's triacid see: a) J. G. Stack, D. P. Curran, J. Rebek, Jr., P. Ballester, J. Am. Chem. Soc. 1991, 113, 5918; b) J. G. Stack, D. P. Curran, S. V. Geib, J. Rebek, Jr., P. Ballester, ibid. 1992, 114, 7007. For examinations of selectivity in radical additions to fumarates and related systems see: N. A. Porter, J. D. Bruhnke, W.-X. Wu, I. J. Rosenstein, R. A. Breyer, J. Am. Chem. Soc. 1992, 114, 7664; B. Giese, M. Zehnder, M. Roth, H.-G. Zeitz, ibid. 1990, 112, 6741; N. A. Porter, D. M. Scott, B. Lacher, B. Giese, H.-G. Zeitz, H. J. Lindner, ibid. 1989, 111, 8311; D. M. Scott, A. T. McPhail, N. A. Porter, Tetrahedron Lett. 1990, 31, 707; M. Bulliard, H.-G. Zeitz, B. Giese, Synlett 1991, 423.
13. For work on radical additions to fumarates using imides derived from Kemp's triacid see: a) J. G. Stack, D. P. Curran, J. Rebek, Jr., P. Ballester, J. Am. Chem. Soc. 1991, 113, 5918; b) J. G. Stack, D. P. Curran, S. V. Geib, J. Rebek, Jr., P. Ballester, ibid. 1992, 114, 7007. For examinations of selectivity in radical additions to fumarates and related systems see: N. A. Porter, J. D. Bruhnke, W.-X. Wu, I. J. Rosenstein, R. A. Breyer, J. Am. Chem. Soc. 1992, 114, 7664; B. Giese, M. Zehnder, M. Roth, H.-G. Zeitz, ibid. 1990, 112, 6741; N. A. Porter, D. M. Scott, B. Lacher, B. Giese, H.-G. Zeitz, H. J. Lindner, ibid. 1989, 111, 8311; D. M. Scott, A. T. McPhail, N. A. Porter, Tetrahedron Lett. 1990, 31, 707; M. Bulliard, H.-G. Zeitz, B. Giese, Synlett 1991, 423.
14. For work on radical additions to fumarates using imides derived from Kemp's triacid see: a) J. G. Stack, D. P. Curran, J. Rebek, Jr., P. Ballester, J. Am. Chem. Soc. 1991, 113, 5918; b) J. G. Stack, D. P. Curran, S. V. Geib, J. Rebek, Jr., P. Ballester, ibid. 1992, 114, 7007. For examinations of selectivity in radical additions to fumarates and related systems see: N. A. Porter, J. D. Bruhnke, W.-X. Wu, I. J. Rosenstein, R. A. Breyer, J. Am. Chem. Soc. 1992, 114, 7664; B. Giese, M. Zehnder, M. Roth, H.-G. Zeitz, ibid. 1990, 112, 6741; N. A. Porter, D. M. Scott, B. Lacher, B. Giese, H.-G. Zeitz, H. J. Lindner, ibid. 1989, 111, 8311; D. M. Scott, A. T. McPhail, N. A. Porter, Tetrahedron Lett. 1990, 31, 707; M. Bulliard, H.-G. Zeitz, B. Giese, Synlett 1991, 423.
15. For work on radical additions to fumarates using imides derived from Kemp's triacid see: a) J. G. Stack, D. P. Curran, J. Rebek, Jr., P. Ballester, J. Am. Chem. Soc. 1991, 113, 5918; b) J. G. Stack, D. P. Curran, S. V. Geib, J. Rebek, Jr., P. Ballester, ibid. 1992, 114, 7007. For examinations of selectivity in radical additions to fumarates and related systems see: N. A. Porter, J. D. Bruhnke, W.-X. Wu, I. J. Rosenstein, R. A. Breyer, J. Am. Chem. Soc. 1992, 114, 7664; B. Giese, M. Zehnder, M. Roth, H.-G. Zeitz, ibid. 1990, 112, 6741; N. A. Porter, D. M. Scott, B. Lacher, B. Giese, H.-G. Zeitz, H. J. Lindner, ibid. 1989, 111, 8311; D. M. Scott, A. T. McPhail, N. A. Porter, Tetrahedron Lett. 1990, 31, 707; M. Bulliard, H.-G. Zeitz, B. Giese, Synlett 1991, 423.
16. For work on radical additions to fumarates using imides derived from Kemp's triacid see: a) J. G. Stack, D. P. Curran, J. Rebek, Jr., P. Ballester, J. Am. Chem. Soc. 1991, 113, 5918; b) J. G. Stack, D. P. Curran, S. V. Geib, J. Rebek, Jr., P. Ballester, ibid. 1992, 114, 7007. For examinations of selectivity in radical additions to fumarates and related systems see: N. A. Porter, J. D. Bruhnke, W.-X. Wu, I. J. Rosenstein, R. A. Breyer, J. Am. Chem. Soc. 1992, 114, 7664; B. Giese, M. Zehnder, M. Roth, H.-G. Zeitz, ibid. 1990, 112, 6741; N. A. Porter, D. M. Scott, B. Lacher, B. Giese, H.-G. Zeitz, H. J. Lindner, ibid. 1989, 111, 8311; D. M. Scott, A. T. McPhail, N. A. Porter, Tetrahedron Lett. 1990, 31, 707; M. Bulliard, H.-G. Zeitz, B. Giese, Synlett 1991, 423.
17. For work on radical additions to fumarates using imides derived from Kemp's triacid see: a) J. G. Stack, D. P. Curran, J. Rebek, Jr., P. Ballester, J. Am. Chem. Soc. 1991, 113, 5918; b) J. G. Stack, D. P. Curran, S. V. Geib, J. Rebek, Jr., P. Ballester, ibid. 1992, 114, 7007. For examinations of selectivity in radical additions to fumarates and related systems see: N. A. Porter, J. D. Bruhnke, W.-X. Wu, I. J. Rosenstein, R. A. Breyer, J. Am. Chem. Soc. 1992, 114, 7664; B. Giese, M. Zehnder, M. Roth, H.-G. Zeitz, ibid. 1990, 112, 6741; N. A. Porter, D. M. Scott, B. Lacher, B. Giese, H.-G. Zeitz, H. J. Lindner, ibid. 1989, 111, 8311; D. M. Scott, A. T. McPhail, N. A. Porter, Tetrahedron Lett. 1990, 31, 707; M. Bulliard, H.-G. Zeitz, B. Giese, Synlett 1991, 423.
18. a) B. K. Park, M. Nakagawa, A. Hirota, M. Nakayama, J. Antibiot. 1988, 41, 751;
19. b) M. M. Murta, M. B. M. de Azevedo, A. E. Greene, J. Org. Chem. 1993, 58, 7537, and references therein.
20. For selected recent examples of the use of Lewis acids in radical reactions see: a) P. Renaud, M. Gerster, J. Am. Chem. Soc. 1995, 117, 6607; b) D. P. Curran, L. H. Kuo, J. Org. Chem. 1994, 59, 3259; c) H. Urabe, K. Yamashita, K. Suzuki, K. Kobayashi, F. Sato, ibid. 1995, 60, 3576; d) M. Murakata, H. Tsutsui, O. Hoshino, J. Chem. Soc. Chem. Commun. 1995, 481; e) J. H. Wu, R. Radinov, N. A. Porter, J. Am. Chem. Soc. 1995, 117, 11029; f) T. Toru, Y. Watanabe, M. Tsusaka, Y. Ueno, ibid. 1993, 115, 10464; g) Y. Guindon, B. Guerrin, C. Chabot, N. Mackintosh, W. W. Ogilvie, Synlett 1995, 449; h) M. B. Andrus, A. B. Argade, X. Chen, M. G. Pamment, Tetrahedron Lett. 1995, 36, 2945; i) K. S. Feldman, A. L. Romaneli, R. E. Ruckle, Jr., G. Jean, J. Org. Chem. 1992, 57, 100.
21. For selected recent examples of the use of Lewis acids in radical reactions see: a) P. Renaud, M. Gerster, J. Am. Chem. Soc. 1995, 117, 6607; b) D. P. Curran, L. H. Kuo, J. Org. Chem. 1994, 59, 3259; c) H. Urabe, K. Yamashita, K. Suzuki, K. Kobayashi, F. Sato, ibid. 1995, 60, 3576; d) M. Murakata, H. Tsutsui, O. Hoshino, J. Chem. Soc. Chem. Commun. 1995, 481; e) J. H. Wu, R. Radinov, N. A. Porter, J. Am. Chem. Soc. 1995, 117, 11029; f) T. Toru, Y. Watanabe, M. Tsusaka, Y. Ueno, ibid. 1993, 115, 10464; g) Y. Guindon, B. Guerrin, C. Chabot, N. Mackintosh, W. W. Ogilvie, Synlett 1995, 449; h) M. B. Andrus, A. B. Argade, X. Chen, M. G. Pamment, Tetrahedron Lett. 1995, 36, 2945; i) K. S. Feldman, A. L. Romaneli, R. E. Ruckle, Jr., G. Jean, J. Org. Chem. 1992, 57, 100.
22. For selected recent examples of the use of Lewis acids in radical reactions see: a) P. Renaud, M. Gerster, J. Am. Chem. Soc. 1995, 117, 6607; b) D. P. Curran, L. H. Kuo, J. Org. Chem. 1994, 59, 3259; c) H. Urabe, K. Yamashita, K. Suzuki, K. Kobayashi, F. Sato, ibid. 1995, 60, 3576; d) M. Murakata, H. Tsutsui, O. Hoshino, J. Chem. Soc. Chem. Commun. 1995, 481; e) J. H. Wu, R. Radinov, N. A. Porter, J. Am. Chem. Soc. 1995, 117, 11029; f) T. Toru, Y. Watanabe, M. Tsusaka, Y. Ueno, ibid. 1993, 115, 10464; g) Y. Guindon, B. Guerrin, C. Chabot, N. Mackintosh, W. W. Ogilvie, Synlett 1995, 449; h) M. B. Andrus, A. B. Argade, X. Chen, M. G. Pamment, Tetrahedron Lett. 1995, 36, 2945; i) K. S. Feldman, A. L. Romaneli, R. E. Ruckle, Jr., G. Jean, J. Org. Chem. 1992, 57, 100.
23. For selected recent examples of the use of Lewis acids in radical reactions see: a) P. Renaud, M. Gerster, J. Am. Chem. Soc. 1995, 117, 6607; b) D. P. Curran, L. H. Kuo, J. Org. Chem. 1994, 59, 3259; c) H. Urabe, K. Yamashita, K. Suzuki, K. Kobayashi, F. Sato, ibid. 1995, 60, 3576; d) M. Murakata, H. Tsutsui, O. Hoshino, J. Chem. Soc. Chem. Commun. 1995, 481; e) J. H. Wu, R. Radinov, N. A. Porter, J. Am. Chem. Soc. 1995, 117, 11029; f) T. Toru, Y. Watanabe, M. Tsusaka, Y. Ueno, ibid. 1993, 115, 10464; g) Y. Guindon, B. Guerrin, C. Chabot, N. Mackintosh, W. W. Ogilvie, Synlett 1995, 449; h) M. B. Andrus, A. B. Argade, X. Chen, M. G. Pamment, Tetrahedron Lett. 1995, 36, 2945; i) K. S. Feldman, A. L. Romaneli, R. E. Ruckle, Jr., G. Jean, J. Org. Chem. 1992, 57, 100.
24. For selected recent examples of the use of Lewis acids in radical reactions see: a) P. Renaud, M. Gerster, J. Am. Chem. Soc. 1995, 117, 6607; b) D. P. Curran, L. H. Kuo, J. Org. Chem. 1994, 59, 3259; c) H. Urabe, K. Yamashita, K. Suzuki, K. Kobayashi, F. Sato, ibid. 1995, 60, 3576; d) M. Murakata, H. Tsutsui, O. Hoshino, J. Chem. Soc. Chem. Commun. 1995, 481; e) J. H. Wu, R. Radinov, N. A. Porter, J. Am. Chem. Soc. 1995, 117, 11029; f) T. Toru, Y. Watanabe, M. Tsusaka, Y. Ueno, ibid. 1993, 115, 10464; g) Y. Guindon, B. Guerrin, C. Chabot, N. Mackintosh, W. W. Ogilvie, Synlett 1995, 449; h) M. B. Andrus, A. B. Argade, X. Chen, M. G. Pamment, Tetrahedron Lett. 1995, 36, 2945; i) K. S. Feldman, A. L. Romaneli, R. E. Ruckle, Jr., G. Jean, J. Org. Chem. 1992, 57, 100.
25. For selected recent examples of the use of Lewis acids in radical reactions see: a) P. Renaud, M. Gerster, J. Am. Chem. Soc. 1995, 117, 6607; b) D. P. Curran, L. H. Kuo, J. Org. Chem. 1994, 59, 3259; c) H. Urabe, K. Yamashita, K. Suzuki, K. Kobayashi, F. Sato, ibid. 1995, 60, 3576; d) M. Murakata, H. Tsutsui, O. Hoshino, J. Chem. Soc. Chem. Commun. 1995, 481; e) J. H. Wu, R. Radinov, N. A. Porter, J. Am. Chem. Soc. 1995, 117, 11029; f) T. Toru, Y. Watanabe, M. Tsusaka, Y. Ueno, ibid. 1993, 115, 10464; g) Y. Guindon, B. Guerrin, C. Chabot, N. Mackintosh, W. W. Ogilvie, Synlett 1995, 449; h) M. B. Andrus, A. B. Argade, X. Chen, M. G. Pamment, Tetrahedron Lett. 1995, 36, 2945; i) K. S. Feldman, A. L. Romaneli, R. E. Ruckle, Jr., G. Jean, J. Org. Chem. 1992, 57, 100.
26. For selected recent examples of the use of Lewis acids in radical reactions see: a) P. Renaud, M. Gerster, J. Am. Chem. Soc. 1995, 117, 6607; b) D. P. Curran, L. H. Kuo, J. Org. Chem. 1994, 59, 3259; c) H. Urabe, K. Yamashita, K. Suzuki, K. Kobayashi, F. Sato, ibid. 1995, 60, 3576; d) M. Murakata, H. Tsutsui, O. Hoshino, J. Chem. Soc. Chem. Commun. 1995, 481; e) J. H. Wu, R. Radinov, N. A. Porter, J. Am. Chem. Soc. 1995, 117, 11029; f) T. Toru, Y. Watanabe, M. Tsusaka, Y. Ueno, ibid. 1993, 115, 10464; g) Y. Guindon, B. Guerrin, C. Chabot, N. Mackintosh, W. W. Ogilvie, Synlett 1995, 449; h) M. B. Andrus, A. B. Argade, X. Chen, M. G. Pamment, Tetrahedron Lett. 1995, 36, 2945; i) K. S. Feldman, A. L. Romaneli, R. E. Ruckle, Jr., G. Jean, J. Org. Chem. 1992, 57, 100.
27. For selected recent examples of the use of Lewis acids in radical reactions see: a) P. Renaud, M. Gerster, J. Am. Chem. Soc. 1995, 117, 6607; b) D. P. Curran, L. H. Kuo, J. Org. Chem. 1994, 59, 3259; c) H. Urabe, K. Yamashita, K. Suzuki, K. Kobayashi, F. Sato, ibid. 1995, 60, 3576; d) M. Murakata, H. Tsutsui, O. Hoshino, J. Chem. Soc. Chem. Commun. 1995, 481; e) J. H. Wu, R. Radinov, N. A. Porter, J. Am. Chem. Soc. 1995, 117, 11029; f) T. Toru, Y. Watanabe, M. Tsusaka, Y. Ueno, ibid. 1993, 115, 10464; g) Y. Guindon, B. Guerrin, C. Chabot, N. Mackintosh, W. W. Ogilvie, Synlett 1995, 449; h) M. B. Andrus, A. B. Argade, X. Chen, M. G. Pamment, Tetrahedron Lett. 1995, 36, 2945; i) K. S. Feldman, A. L. Romaneli, R. E. Ruckle, Jr., G. Jean, J. Org. Chem. 1992, 57, 100.
28. For selected recent examples of the use of Lewis acids in radical reactions see: a) P. Renaud, M. Gerster, J. Am. Chem. Soc. 1995, 117, 6607; b) D. P. Curran, L. H. Kuo, J. Org. Chem. 1994, 59, 3259; c) H. Urabe, K. Yamashita, K. Suzuki, K. Kobayashi, F. Sato, ibid. 1995, 60, 3576; d) M. Murakata, H. Tsutsui, O. Hoshino, J. Chem. Soc. Chem. Commun. 1995, 481; e) J. H. Wu, R. Radinov, N. A. Porter, J. Am. Chem. Soc. 1995, 117, 11029; f) T. Toru, Y. Watanabe, M. Tsusaka, Y. Ueno, ibid. 1993, 115, 10464; g) Y. Guindon, B. Guerrin, C. Chabot, N. Mackintosh, W. W. Ogilvie, Synlett 1995, 449; h) M. B. Andrus, A. B. Argade, X. Chen, M. G. Pamment, Tetrahedron Lett. 1995, 36, 2945; i) K. S. Feldman, A. L. Romaneli, R. E. Ruckle, Jr., G. Jean, J. Org. Chem. 1992, 57, 100.
29. Substrate 7 was prepared in 87% yield by acylation of the chiral auxiliary with the acid chloride derived from commercially available monoethyl fumaric acid.
30. For the preparation of the oxazolidinone derived from diphenylalanine see: M. P. Sibi, P. K. Deshpande, A. J. La Loggia, J. W. Christensen, Tetrahedron Lett. 1995, 36, 8961.
31. The regioselectivity in the radical addition experiments was determined by NMR analysis of the reaction mixture. Authentic samples of the racemic regioand diastereomeric (1:1) monoethyl succinic acids were prepared by independent synthesis (ref. [3b]) and the chiral auxiliary introduced by standard techniques. The 400 MHz NMR spectra of the four regio-and diastereomeric products show well-separated signals for the methylene protons, which allowed unambiguous determination of product ratios.
32. 3) were also evaluated but they showed inferior selectivity.
33. 2; MeMgBr, CuCN; MeLi, CuCN.
34. Minor amounts of ethyl radical addition (from triethylborane) were also observed.
35. Older batches of tributyltin hydride led to some epimerization.
36. M. P. Sibi, P. K. Deshpande, A. J. La Loggia, Synlett 1996, 343.
37. a) J. R. Gage, D. A. Evans, Org. Synth. 1989, 68, 83;
38. b) D. L. Boger, S. L. Colletti, T. Honda, R. F. Menezes, J. Am. Chem. Soc. 1994, 116, 5607.
39. The chiral auxiliary was recovered in 99% yield.
40. 3); H. Takahata, Y. Uchida, T. Momose, J. Org. Chem. 1995, 60, 5628; Tetrahedron Lett. 1994, 35, 4123.
41. 3); H. Takahata, Y. Uchida, T. Momose, J. Org. Chem. 1995, 60, 5628; Tetrahedron Lett. 1994, 35, 4123.
42. 3)]; J. Mulzer, N. Salimi, H. Hartl, Tetrahedron: Asymmetry 1993, 4, 457; H. Takahata, Y. Uchida, T. Momose, J. Org. Chem. 1995, 60, 5628.
43. 3)]; J. Mulzer, N. Salimi, H. Hartl, Tetrahedron: Asymmetry 1993, 4, 457; H. Takahata, Y. Uchida, T. Momose, J. Org. Chem. 1995, 60, 5628.
44. The installation of the C-3 methyl group by enolate alkylation of the butyrolactone proceeds in low yields and is possible only with the carboxyl group as the C-4 substituent; M. P. Sibi, J. Ji et al., unpublished results.