The stereochemical dichotomy in palladium(0)- and nickel(0)-catalyzed allylic substitution

Journal of the American Chemical Society

Volumn 120, Issue 27, 1998, Pages 6661-6672

  Farthing, Christopher N ^a   Kočovský, Pavel ^a  

^a UNIVERSITY OF LEICESTER   (United Kingdom)

Author keywords

[No Author keywords available]

Indexed keywords

ALLYL COMPOUND;

ARTICLE; CATALYSIS; DRUG SYNTHESIS; IN VITRO STUDY; MODEL; NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY; REACTION ANALYSIS; STEREOCHEMISTRY;

EID: 2642670293     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja980222l     Document Type: Article

References (100)

1. (a) Trost, B. M.; Strege, P. E. J. Am. Chem. Soc. 1975, 97, 2534.
2. (b) Trost, B. M.; Verhoeven, T. R. J. Org. Chem. 1976, 41, 3215.
3. (c) Hayashi, T.; Hagihara, T.; Konishi, M.; Kumada, M. J. Am. Chem. Soc. 1983, 105, 7767.
4. For reviews, see: (d) Trost, B. M. Tetrahedron 1977, 33, 371.
5. (e) Trost, B. M. Acc. Chem. Res. 1980, 13, 385.
6. (f) Tsuji, J. Tetrahedron 1986, 42, 4361.
7. (g) Frost, C. G.; Howarth, J.; Williams, J. M. J. Tetrahedron: Asymmetry 1992, 3, 1089.
8. (h) Trost, B. M.; Van Vranken, D. L. Chem. Rev. 1996, 96, 395.
9. Trost, B. M. Acc. Chem. Res. 1996, 29, 355.
10. (a) Temple, J. S.; Schwartz, J. J. Am. Chem. Soc. 1980, 102, 7381.
11. (b) Matsushida, H.; Negishi, E. J. Chem. Soc., Chem. Commun. 1982, 160.
12. (c) Temple, J. S.; Riediker, M.; Schwartz, J. J. Am. Chem. Soc. 1982, 104, 1310.
13. (d) Labadie, J. W.; Stille, J. K. J. Am. Chem. Soc. 1983, 105, 6129.
14. (e) Goliaszewski, A.; Schwartz, J. J. Am. Chem. Soc. 1984, 106, 5028.
15. (f) Keinan, E.; Roth, Z. J. Org. Chem. 1983,48, 1769.
16. (g) Fiaud, J.-C.; Legros, J.-Y. J. Org. Chem. 1987, 52, 1907.
17. (a) Trost, B. M.; Lautens, M. J. Am. Chem. Soc. 1982, 104, 5543.
18. (b) Trost, B. M.; Lautens, M. J. Am. Chem. Soc. 1983, 105, 3343.
19. (c) Trost, B. M.; Lautens, M. Organometallics 1983, 2, 1687.
20. (d) Trost, B. M.; Lautens, M.; Peterson, B. Tetrahedron Lett. 1983, 24, 4525.
21. (e) Trost, B. M.; Lautens, M. J. Am. Chem. Soc. 1987, 109, 1469.
22. (f) Trost, B. M.; Lautens, M. Tetrahedron 1987, 43, 4817.
23. (g) Trost, B. M.; Merlic, C. A. J. Am. Chem. Soc. 1990, 112, 9590.
24. Dvořák, D.; Starý, I.; Kočovský, P. J. Am. Chem. Soc. 1995, 117, 6130.
25. 3-complex, proceeds with inversion in the second step (1 → 4 → 5): (a) Faller, J. W.; Linebarrier, D. Organometallics 1988, 7, 1670. (b) Ward, Y. D.; Villanueva, L. A.; Allerd, G. D.; Liebeskind, L. S. J. Am. Chem. Soc. 1996, 118, 897.
26. 3-complex, proceeds with inversion in the second step (1 → 4 → 5): (a) Faller, J. W.; Linebarrier, D. Organometallics 1988, 7, 1670. (b) Ward, Y. D.; Villanueva, L. A.; Allerd, G. D.; Liebeskind, L. S. J. Am. Chem. Soc. 1996, 118, 897.
27. (a) Starý, I.; Kočovský, P. J. Am. Chem. Soc. 1989, 111, 4981.
28. (b) Starý, I.; Zajíček, J.; Kočovský, P. Tetrahedron 1992, 48, 7229.
29. (a) Kurosawa, H.; Ogoshi, S.; Kawasaki, Y.; Murai, S.; Miyoshi, M.; Ikeda, I. J. Am. Chem. Soc. 1990, 112, 2813.
30. (b) Kurosawa, H.; Kajimaru, H.; Ogoshi, S.; Yoneda, H.; Miki, K.; Kasai, N.; Murai, S.; Ikeda, I. J. Am. Chem. Soc. 1992, 114, 8417.
31. 2), the mechanism apparently involves the usual inversion 1 → 2 followed by thermodynamic equilibration 2 → 4: Vitagliano, A.; Åkermark, B.; Hanson, S. Organometallics 1991, 10, 2592.
32. (a) Bäckvall, J.-E.; Nordberg, R. E. J. Am. Chem. Soc. 1981, 103, 4959.
33. (b) Bäckvall, J.-E.; Byström, S. E.; Nordberg, R. E. J. Org. Chem. 1984, 49, 4619.
34. (c) Bäckvall, J.-E.; Nyström, J.-E.; Nordberg, R. E. J. Am. Chem. Soc. 1985, 107, 3676.
35. (d) Bäckvall, J.-E.; Nordberg, R. E.; Wilhelm, D. J. Am. Chem. Soc. 1985, 107, 6892.
36. For reviews, see: (e) Bäckvall, J.-E. Acc. Chem. Res. 1983, 16, 335.
37. (f) Bäckvall, J.-E. Pure Appl. Chem. 1992, 64, 429; Pure Appl. Chem. 1996, 68, 535.
38. (f) Bäckvall, J.-E. Pure Appl. Chem. 1992, 64, 429; Pure Appl. Chem. 1996, 68, 535.
39. (g) Bäckvall, J.-E. Acta Chem. Scand. 1996, 50, 661.
40. (a) Nyström, J.-E.; Rein, T.; Bäckvall, J.-E. Org. Synth. 1989, 67, 105.
41. (b) Bäckvall, J.-E.; Granberg, K. L.; Hopkins, R. B. Acta Chem. Scand. 1990, 44, 492.
42. While this work was in progress, Bäckvall published the same transformation in the cyclohexane series (7a → 8a): Gatti, R. G. P.; Carson, A. L. E.; Bäckvall, J.-E. J. Chem. Soc., Perkin Trans. 1 1997, 577.
43. For reviews on steering the reagent/catalyst by a neighboring group, see: (a) Hoveyda, A. H.; Evans, D. A.; Fu, G. C. Chem. Rev. 1993, 93, 1307. (b) Brown, J. M. Angew. Chem., Int Ed. Engl. 1987, 26, 190. See also: (c) Crabtree, R. H.; Davis, M. W. J. Org. Chem. 1986. 51, 2655. (d) Burk, M. J.; McGrath, M. P.; Wheeler, R.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 110, 5034. For recent examples, see, e.g.: (e) Kočovský, P. J. Chem. Soc., Perkin Trans. 1 1994, 1759 and references therein. (f) Breit, B. J. Chem. Soc., Chem. Commun. 1997, 591. (g) Breit, B. Angew. Chem., Int. Ed. 1997, 35, 2835.
44. For reviews on steering the reagent/catalyst by a neighboring group, see: (a) Hoveyda, A. H.; Evans, D. A.; Fu, G. C. Chem. Rev. 1993, 93, 1307. (b) Brown, J. M. Angew. Chem., Int Ed. Engl. 1987, 26, 190. See also: (c) Crabtree, R. H.; Davis, M. W. J. Org. Chem. 1986. 51, 2655. (d) Burk, M. J.; McGrath, M. P.; Wheeler, R.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 110, 5034. For recent examples, see, e.g.: (e) Kočovský, P. J. Chem. Soc., Perkin Trans. 1 1994, 1759 and references therein. (f) Breit, B. J. Chem. Soc., Chem. Commun. 1997, 591. (g) Breit, B. Angew. Chem., Int. Ed. 1997, 35, 2835.
45. For reviews on steering the reagent/catalyst by a neighboring group, see: (a) Hoveyda, A. H.; Evans, D. A.; Fu, G. C. Chem. Rev. 1993, 93, 1307. (b) Brown, J. M. Angew. Chem., Int Ed. Engl. 1987, 26, 190. See also: (c) Crabtree, R. H.; Davis, M. W. J. Org. Chem. 1986. 51, 2655. (d) Burk, M. J.; McGrath, M. P.; Wheeler, R.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 110, 5034. For recent examples, see, e.g.: (e) Kočovský, P. J. Chem. Soc., Perkin Trans. 1 1994, 1759 and references therein. (f) Breit, B. J. Chem. Soc., Chem. Commun. 1997, 591. (g) Breit, B. Angew. Chem., Int. Ed. 1997, 35, 2835.
46. For reviews on steering the reagent/catalyst by a neighboring group, see: (a) Hoveyda, A. H.; Evans, D. A.; Fu, G. C. Chem. Rev. 1993, 93, 1307. (b) Brown, J. M. Angew. Chem., Int Ed. Engl. 1987, 26, 190. See also: (c) Crabtree, R. H.; Davis, M. W. J. Org. Chem. 1986. 51, 2655. (d) Burk, M. J.; McGrath, M. P.; Wheeler, R.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 110, 5034. For recent examples, see, e.g.: (e) Kočovský, P. J. Chem. Soc., Perkin Trans. 1 1994, 1759 and references therein. (f) Breit, B. J. Chem. Soc., Chem. Commun. 1997, 591. (g) Breit, B. Angew. Chem., Int. Ed. 1997, 35, 2835.
47. For reviews on steering the reagent/catalyst by a neighboring group, see: (a) Hoveyda, A. H.; Evans, D. A.; Fu, G. C. Chem. Rev. 1993, 93, 1307. (b) Brown, J. M. Angew. Chem., Int Ed. Engl. 1987, 26, 190. See also: (c) Crabtree, R. H.; Davis, M. W. J. Org. Chem. 1986. 51, 2655. (d) Burk, M. J.; McGrath, M. P.; Wheeler, R.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 110, 5034. For recent examples, see, e.g.: (e) Kočovský, P. J. Chem. Soc., Perkin Trans. 1 1994, 1759 and references therein. (f) Breit, B. J. Chem. Soc., Chem. Commun. 1997, 591. (g) Breit, B. Angew. Chem., Int. Ed. 1997, 35, 2835.
48. For reviews on steering the reagent/catalyst by a neighboring group, see: (a) Hoveyda, A. H.; Evans, D. A.; Fu, G. C. Chem. Rev. 1993, 93, 1307. (b) Brown, J. M. Angew. Chem., Int Ed. Engl. 1987, 26, 190. See also: (c) Crabtree, R. H.; Davis, M. W. J. Org. Chem. 1986. 51, 2655. (d) Burk, M. J.; McGrath, M. P.; Wheeler, R.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 110, 5034. For recent examples, see, e.g.: (e) Kočovský, P. J. Chem. Soc., Perkin Trans. 1 1994, 1759 and references therein. (f) Breit, B. J. Chem. Soc., Chem. Commun. 1997, 591. (g) Breit, B. Angew. Chem., Int. Ed. 1997, 35, 2835.
49. For reviews on steering the reagent/catalyst by a neighboring group, see: (a) Hoveyda, A. H.; Evans, D. A.; Fu, G. C. Chem. Rev. 1993, 93, 1307. (b) Brown, J. M. Angew. Chem., Int Ed. Engl. 1987, 26, 190. See also: (c) Crabtree, R. H.; Davis, M. W. J. Org. Chem. 1986. 51, 2655. (d) Burk, M. J.; McGrath, M. P.; Wheeler, R.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 110, 5034. For recent examples, see, e.g.: (e) Kočovský, P. J. Chem. Soc., Perkin Trans. 1 1994, 1759 and references therein. (f) Breit, B. J. Chem. Soc., Chem. Commun. 1997, 591. (g) Breit, B. Angew. Chem., Int. Ed. 1997, 35, 2835.
50. All yields refer to "isolated" yields.
51. The Mitsunobu reaction using the alcohol obtained on saponification of either acetate 13 or 14 failed to produce the required syn-epimer, giving mainly elimination products.
52. Yamamoto, Y.; Yatagai, H.; Maruyama, K.; Sonoda, A.; Murahashi, S. J. Am. Chem. Soc. 1977, 99, 5652.
53. For the method, see: Zweifel, G.; Miller, R. L. J. Am. Chem. Soc. 1970, 92, 6678.
54. 2Pd, p-benzoquinone, LiCl, and AcOLi in an AcOH-hexane mixture proved essential for the reaction to proceed with acceptable efficiency, with the formation of the products of the competing Diels-Alder addition of p-BQ to the diene 18 being substantially reduced.
55. 1H NMR, as derived from a large series of compounds, see: Nordberg, R. Thesis, Royal Institute of Technology, Stockholm, 1982. The characteristic features are as follows: chemical shifts of the corresponding allylic protons are consistently higher for the trans-series by ∼0.1 ppm and their W/2 values (width at half-height of the multiplet) are typically twice as large. Thus, (E)-1,4-diacetoxycyclohex-2-ene shows CH-OAc at δ 5.32 (m, W/2 = 11 Hz), whereas its Z-counterpart exhibits this proton at δ 5.23 (m, W/2 = 8 Hz). Analogously, the products of monosubstitution of the latter diacetates with malonate give the following values for the allylic protons: 2.98 (m) and 5.28 (m, W/2 = 16 Hz) for the E-isomer and 2.88 (m) and 5.19 (m, W/2 = 9 Hz) for the Z-isomer. The data obtained for our compounds are in line with this generalization.
56. (a) Mitsunobu, O. Synthesis 1981, 1.
57. (b) Shull, B. K.; Sakai, T.; Nichols, J. B.; Koreeda, M. J. Org. Chem. 1997, 62, 8294.
58. 2 singlet at 5.00 ppm), the corresponding proton in 27a appears at 5.17 ppm as ddd (J = 3, 5.5, and 9 Hz).
59. n at 29.3, 127.3, and 129.4 ppm.
60. 22
61. 3-complexes of Pd, see ref 23.
62. Granberg, K. L.; Bäckvall, J.-E. J. Am. Chem. Soc. 1992, 114, 6858. For correction, see: J. Am. Chem. Soc. 1994, 116, 10853.
63. Granberg, K. L.; Bäckvall, J.-E. J. Am. Chem. Soc. 1992, 114, 6858. For correction, see: J. Am. Chem. Soc. 1994, 116, 10853.
64. (a) Auburn, P. R.; Mackenzie, P. B.; Bosnich, B. J. Am. Chem. Soc. 1985, 107, 2033.
65. (b) Mackenzie, P. B.; Whelan, J.; Bosnich, B. J. Am. Chem. Soc. 1985, 107, 2046.
66. The "Bosnich mechanism" was actually first proposed by Collman and Hegedus: (a) Collman, J. P.; Hegedus, L. S. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1980; p 692. For further examples, see refs 6b, 8, 23, 26, and (b) Bäckvall, J.-E.; Vågberg, J. O.; Zercher, G.; Genêt, J. P.; Denis, A. J. Org. Chem. 1987, 52, 5430. (c) Moreno-Mañas, M.; Ribas, J.; Virgili, A. J. Org. Chem. 1988, 53, 5328. (d) Kurosawa, H.; Ogoshi, S.; Chatani, N.; Kawasaki, Y.; Murai, S.; Ikeda, I. Chem. Lett. 1990, 1745.
67. The "Bosnich mechanism" was actually first proposed by Collman and Hegedus: (a) Collman, J. P.; Hegedus, L. S. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1980; p 692. For further examples, see refs 6b, 8, 23, 26, and (b) Bäckvall, J.-E.; Vågberg, J. O.; Zercher, G.; Genêt, J. P.; Denis, A. J. Org. Chem. 1987, 52, 5430. (c) Moreno-Mañas, M.; Ribas, J.; Virgili, A. J. Org. Chem. 1988, 53, 5328. (d) Kurosawa, H.; Ogoshi, S.; Chatani, N.; Kawasaki, Y.; Murai, S.; Ikeda, I. Chem. Lett. 1990, 1745.
68. The "Bosnich mechanism" was actually first proposed by Collman and Hegedus: (a) Collman, J. P.; Hegedus, L. S. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1980; p 692. For further examples, see refs 6b, 8, 23, 26, and (b) Bäckvall, J.-E.; Vågberg, J. O.; Zercher, G.; Genêt, J. P.; Denis, A. J. Org. Chem. 1987, 52, 5430. (c) Moreno-Mañas, M.; Ribas, J.; Virgili, A. J. Org. Chem. 1988, 53, 5328. (d) Kurosawa, H.; Ogoshi, S.; Chatani, N.; Kawasaki, Y.; Murai, S.; Ikeda, I. Chem. Lett. 1990, 1745.
69. The "Bosnich mechanism" was actually first proposed by Collman and Hegedus: (a) Collman, J. P.; Hegedus, L. S. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1980; p 692. For further examples, see refs 6b, 8, 23, 26, and (b) Bäckvall, J.-E.; Vågberg, J. O.; Zercher, G.; Genêt, J. P.; Denis, A. J. Org. Chem. 1987, 52, 5430. (c) Moreno-Mañas, M.; Ribas, J.; Virgili, A. J. Org. Chem. 1988, 53, 5328. (d) Kurosawa, H.; Ogoshi, S.; Chatani, N.; Kawasaki, Y.; Murai, S.; Ikeda, I. Chem. Lett. 1990, 1745.
70. Bäckvall, J.-E.; Granberg, K. L.; Heumann, A. Isr. J. Chem. 1991, 31, 17.
71. 23,26 However, the reaction of 9 with malonate anion proved to be highly stereoselective (vide supra) so that this possibility can be ruled out.
72. 2CH, their steric effect on the ultimate environment of the double bond is, in fact, similar, as revealed by molecular modeling. Therefore, if only the steric effect of the N-substituent were taken into account, little difference in reactivity (i.e., in the reaction rate) would be anticipated for 9 and 10.
73. Note that this analysis lends further credence to the rejection of a similar mechanism for the cyclic series (Scheme 7).
74. (a) Consiglio, G.; Morandini, F.; Piccolo, O. J. Am. Chem. Soc. 1981, 103, 1846.
75. (b) Consiglio, G.; Piccolo, O.; Roncetti, L.; Morandini, F. Tetrahedron 1986, 41, 2043.
76. (a) Didiuk, M. T.; Morken, J. P.; Hoveyda, A. H. J. Am. Chem. Soc. 1995, 117, 7273.
77. (b) Didiuk, M. T.; Morken, J. P.; Hoveyda, A. H. Tetrahedron 1998, 54, 1117.
78. 2O at room temperature for 2 h, is capricious and the procedure shown in the Experimental Section represents the most successful batch.
79. For an alternative synthesis of 48, see: Rabasco, J.; Kass, S. R. J. Org. Chem. 1993, 58, 2633.
80. 2. However, in view of the stoichiometric nature of this reaction, it was only used in order to obtain an authentic sample of 49.
81. Bäckvall, J.-E.; Nordberg, R. E.; Zetterberg, K.; Åkermark, B. Organometallics 1983, 2, 1625.
82. The maximum deviation from the perfect alignment that is tolerated, seems to be ∼30°, as derived from the investigation of Wagner-Meerwein rearrangements in a series of rigid, polycyclic skeletons: Saunders: M.; Chandrasekhar, J.; Schleyer, P. v. R. Rearrangements of Carbocations. In Rearrangements in Ground and Excited States; de Mayo, P., Ed.; Academic: New York, 1980: Vol. 1, pp 24-34.
83. This scenario parallels the occurrence of both anti-and synmechanisms for the E2 elimination reactions. For leading reviews, see: (a) Sicher, J. Angew. Chem., Int. Ed. Engl. 1972, 11, 200. (b) Sicher, J. Pure Appl. Chem. 1971, 22, 655. (c) Bartsch, R. A.; Závada, J. Chem. Rev. 1980, 80, 453.
84. This scenario parallels the occurrence of both anti-and synmechanisms for the E2 elimination reactions. For leading reviews, see: (a) Sicher, J. Angew. Chem., Int. Ed. Engl. 1972, 11, 200. (b) Sicher, J. Pure Appl. Chem. 1971, 22, 655. (c) Bartsch, R. A.; Závada, J. Chem. Rev. 1980, 80, 453.
85. This scenario parallels the occurrence of both anti-and synmechanisms for the E2 elimination reactions. For leading reviews, see: (a) Sicher, J. Angew. Chem., Int. Ed. Engl. 1972, 11, 200. (b) Sicher, J. Pure Appl. Chem. 1971, 22, 655. (c) Bartsch, R. A.; Závada, J. Chem. Rev. 1980, 80, 453.
86. N2′), see: (b) Magid, R. M. Tetrahedron 1980, 36, 1901.
87. N2′), see: (b) Magid, R. M. Tetrahedron 1980, 36, 1901.
88. (c) Paquette, L. A.; Stirling, C. J. M. Tetrahedron 1992, 48, 7383.
89. (a) Corey, E. J.; Boaz, N. W. Tetrahedron Lett. 1984, 25, 3063.
90. (b) Corey, E. J.; Hannon, F. J. Tetrahedron Lett. 1990, 31, 1393.
91. (c) Hill, R. S.; Becalska, A.; Chiem, N. Organometallics 1991, 10, 2104.
92. Bäckvall, J.-E.; Juntunen, S. K. J. Am. Chem. Soc. 1987, 109, 6396.
93. Krafft, M. E.; Wilson, A. M.; Fu, Z.; Procter, M. J.; Dasse, O. A. J. Org. Chem. 1998, 63, 1748.
94. For a similar stereochemical switch in the cuprate-mediated allylic substitution, see: (a) Gallina, C.; Ciattini, P. G.; J. Am. Chem. Soc. 1979, 101, 1035. (b) Goering, H. L.; Kantner, S. S.; Tseng, C. C. J. Org. Chem. 1983, 48, 715. (c) Tseng, C. C.; Yen, S. J.; Goering, H. L. J. Org. Chem. 1986, 51, 2892 and refs given therein. (d) Valverde, S.; Bernabé, M.; Garcia-Ochoa, S.; Gómez, A. M. J. Org. Chem. 1990, 55, 2294 and refs given therein.
95. For a similar stereochemical switch in the cuprate-mediated allylic substitution, see: (a) Gallina, C.; Ciattini, P. G.; J. Am. Chem. Soc. 1979, 101, 1035. (b) Goering, H. L.; Kantner, S. S.; Tseng, C. C. J. Org. Chem. 1983, 48, 715. (c) Tseng, C. C.; Yen, S. J.; Goering, H. L. J. Org. Chem. 1986, 51, 2892 and refs given therein. (d) Valverde, S.; Bernabé, M.; Garcia-Ochoa, S.; Gómez, A. M. J. Org. Chem. 1990, 55, 2294 and refs given therein.
96. For a similar stereochemical switch in the cuprate-mediated allylic substitution, see: (a) Gallina, C.; Ciattini, P. G.; J. Am. Chem. Soc. 1979, 101, 1035. (b) Goering, H. L.; Kantner, S. S.; Tseng, C. C. J. Org. Chem. 1983, 48, 715. (c) Tseng, C. C.; Yen, S. J.; Goering, H. L. J. Org. Chem. 1986, 51, 2892 and refs given therein. (d) Valverde, S.; Bernabé, M.; Garcia-Ochoa, S.; Gómez, A. M. J. Org. Chem. 1990, 55, 2294 and refs given therein.
97. For a similar stereochemical switch in the cuprate-mediated allylic substitution, see: (a) Gallina, C.; Ciattini, P. G.; J. Am. Chem. Soc. 1979, 101, 1035. (b) Goering, H. L.; Kantner, S. S.; Tseng, C. C. J. Org. Chem. 1983, 48, 715. (c) Tseng, C. C.; Yen, S. J.; Goering, H. L. J. Org. Chem. 1986, 51, 2892 and refs given therein. (d) Valverde, S.; Bernabé, M.; Garcia-Ochoa, S.; Gómez, A. M. J. Org. Chem. 1990, 55, 2294 and refs given therein.
98. Breit, B. Angew. Chem., Int. Ed. 1998, 37, 525.
99. 43 requires the coordinating group to be located at the carbon more distant than in the δ-position.
100. Andersson, P. G. J. Org. Chem. 1996, 61, 4154.