Mechanism of stereoinduction in asymmetric synthesis of highly functionalized 1,2-dihydroquinolines and 2H-1-benzopyrans via nonracemic palladacycles with a metal-bonded stereogenic carbon

Journal of Organic Chemistry

Volumn 69, Issue 14, 2004, Pages 4701-4715

  Lu, Genliang ^a   Malinakova, Helena C ^a  

^a UNIVERSITY OF KANSAS   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

AROMATIC COMPOUNDS; CHEMICAL BONDS; COMPLEXATION; ESTERS;

CHIRALITY; STEREOCENTERS;

STEREOCHEMISTRY;

1,2 DIHYDROQUINOLINE DERIVATIVE; 2H 1 BENZOPYRAN DERIVATIVE; ACETIC ACID; ALKYNE; BENZOPYRAN DERIVATIVE; CARBON; CYCLOHEXANE DERIVATIVE; DIHYDROQUINOLINE DERIVATIVE; ESTER; HETEROCYCLIC COMPOUND; IODIDE; IODINE DERIVATIVE; LIGAND; N,N,N',N' TETRAMETHYL 1,2 DIAMINOCYCLOHEXANE; PALLADIUM; TRIPHENYLPHOSPHINE; UNCLASSIFIED DRUG;

ARTICLE; CHIRALITY; CONFORMATION; DIASTEREOISOMER; METAL BINDING; MOLECULAR DYNAMICS; RACEMIC MIXTURE; REACTION ANALYSIS; STEREOCHEMISTRY; SYNTHESIS;

EID: 3142609043     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo040148r     Document Type: Article

References (136)

1. Söderberg, B. C. G. Coord. Chem. Rev. 2003, 241, 147-247.
2. (a) Metal-Catalyzed Cross-Coupling Reactions; Diederich, F., Stang, P. J., Eds.; Wiley-VCH Verlag GmBH: Weinhein, 1998.
3. (b) Handbook of Organopalladium Chemistry for Organic Synthesis; Negishi, E.-I., Ed.; John Wiley & Sons: New York, 2002.
4. (a) Hayashi, T.; Konishi, M.; Okamoto, Y.; Kabeta, K.; Kumada, M. J. Org. Chem. 1986, 51, 3772-3781.
5. (b) Hayashi, T.; Konishi, M.; Fukushima, M.; Mise, T.; Kagotami, M.; Tajika, M.; Kumada, M. J. Am. Chem. Soc. 1982, 104, 180-186.
6. (c) Cardellichio, C.; Fiandanese, V.; Naso, F. Gazz. Chim. Ital. 1991, 121, 11-16.
7. (a) Hamada, T.; Chieffi, A.; Åhman, J.; Buchwald, S. J. Am. Chem. Soc. 2002, 124, 1261-1268.
8. (b) Hamada, T.; Buchwald, S. L. Org. Lett. 2002, 4, 999-1001.
9. (c) Ahman, J.; Wolfe, J. P.; Troutman, M. V., Palucki, M.; Buchwald, S. L. J. Am. Chem. Soc. 1998, 120, 1918-1919.
10. (d) Lee, S.; Hartwig, J. F. J. Org. Chem. 2001, 66, 3402-3415.
11. (e) Spielvogel, D. J.; Buchwald, S. L. J. Am. Chem. Soc. 2002, 124, 3500-3501.
12. (a) Singh, U. K.; Strieter, E. R.; Blackmond, D. G.; Buchwald, S. L. J. Am. Chem. Soc. 2002, 124, 14104-14114.
13. (b) Albeniz, A. C.; Espinet, P.; Martin-Ruiz, B. Chem. Eur. J. 2001, 7, 2481-2489.
14. (c) Principles and Applications of Organotransition Metal Chemistry; Collman, J. P., Hegedus, L. S., Finke, R. G., Eds.; University Science Books: Mill Valley, CA, 1987.
15. (d) Huggins, J. M.; Bergman, R. G. J. Am. Chem. Soc. 1981, 103, 3002-3011.
16. (e) Fitton, P.; Rick, E. A. J. Organomet. Chem. 1971, 28, 287-291.
17. (a) Ryabov, A. D.; Panyashkina, I. M.; Polyakov, V. A.; Fisher, A. Organometallics 2002, 21, 1633-1636.
18. (b) Hashmi, A. S. K.; Naumann, F.; Bolte, M. Organometallics 1998, 17, 2385-2387.
19. (c) Flood, T. C.; Holcomb, H. L.; Nakanishi, S. Organometallics 1996, 15, 4228-4234.
20. (d) Garcia-Ruano, J. L.; Gonzalez, A. N.; Barcena, A. I.; Camazon, M. J.; Navarro-Ranninger, C. Tetrahedron: Asymmetry 1996, 7, 139-148.
21. (e) Bergman, R. G.; Mobley, T. A.; Schade, C. J. Am. Chem. Soc. 1995, 117, 7822-7823.
22. (f) Yoneda, A.; Hakushi, T.; Newkome, G. R.; Fronczek, F. R. Organometallics 1994, 13, 4912-4918.
23. (g) Pfeffer, M.; Spencer, J.; Maassarani, F.; DeCian, A.; Fisher, J. Tetrahedron: Asymmetry 1994, 5, 321-324.
24. (h) Dunina, V. V.; Golovan, E. B.; Kazakova, E. I.; Potapov, G. P.; Beletskaya, I. P. Metalloorg. Khim. 1991, 4, 1391-1396;
25. (a) Catellani, M. Synlett 2003, 298-313.
26. (b) Lautens, M.; Paquin, J.-F.; Piguel, S. J. Org. Chem. 2002, 67, 3972-3974.
27. (c) Larock, R. C.; Tian, Q. J. Org. Chem. 2001, 66, 7372-7379.
28. (d) Wang, L.; Pan, Y.; Jiang, X.; Hu, H. Tetrahedron Lett. 2000, 41, 725-727.
29. (e) Catellani, M.; Motti, E.; Baratta, S. Org. Lett. 2001, 3, 3611-3614.
30. (f) Dyker, G. Chem. Ber. 1997, 130, 1567-1578.
31. (g) Catellani, M.; Frignani, F.; Rangoni, A. Angew. Chem., Int. Ed. Engl. 1997, 36, 119-122.
32. (h) Echavarren, A. M.; Gonzalez, J. J.; Garcia, N.; Gomez-Lor, B. J. Org. Chem. 1997, 62, 1286-1291.
33. (i) Dyker, G. J. Org. Chem. 1993, 58, 6426-6428.
34. (j) Dyker, G. Angew. Chem., Int. Ed. Engl. 1994, 33, 103-105.
35. For examples of the preparation of stable palladacycles, see: (a) Martin-Matute, B.; Mateo, C.; Cardenas, D. J.; Echavarren, A. M. Chem. Eur. J. 2001, 7, 2341-2348.
36. (b) Mateo, C.; Fernandez-Rivas, C.; Cardenas, D. J.; Echavarren, A. M. Organometallics 1998, 17, 3661-3669.
37. (c) van Belzen, R.; Hoffmann, H.; Elsevier, C. J. Angew. Chem., Int. Ed. Engl. 1997, 36, 1743-1745.
38. (d) Catellani, M.; Chiusoli, G. P. J. Organomet. Chem. 1988, 346, C27-C30.
39. (e) Diversi, P.; Ingrosso, G.; Lucherini, A.; Murtas, S. J. Chem. Soc., Dalton 1980, 9, 1633-1637.
40. (f) Munz, D.; Stephan, C.; Dieck, H. T. J. Organomet. Chem. 1991, 407, 413-420.
41. Portscheller, J. L.; Malinakova, H. C. Org. Lett. 2002, 4, 3679-3681.
42. For alkyne insertions to group 10 metalacycles and cyclometalated complexes, see: (a) Campora, J.; Palma, P.; Carmona, E. Coord. Chem. Rev. 1999, 193-195; 207-281.
43. (b) Campora, J.; Paneque, M.; Poveda, M. L.; Carmona, E. Synlett 1994, 465-470.
44. (c) Liu, C.-H.; Li, C.-S.; Cheng, C.-H. Organometallics 1994, 13, 18-20.
45. (d) Pfeffer, M.; Rotteweel, M. A. J. Org. Chem. 1992, 57, 2147-2154.
46. (e) Pfeffer, M. Recl. Trav. Chim. Pays-Bas 1990, 109, 567-576.
47. Portscheller, J. L.; Lilley, S. E.; Malinakova, H. C. Organometallics 2003, 22, 2961-2971.
48. For selected examples of biologically active 1,2-dihydroquinolines, see: (a) Elmore, S. W.; Coghlan, M. J.; Anderson, D. D.; Pratt, J. K.; Green, B. E.; Wang, A. X.; Staschko, M. A.; Lin, C. W.; Tyree, C. M.; Miner, J. N.; Jacobson, P. B.; Wilcox, D. M.; Lane, B. C. J. Med. Chem. 2001, 44, 4481-4491.
49. (b) Zhi, L.; Tegley, C. M.; Marschke, K. B.; Mais, D. E.; Jones, T. K. J. Med. Chem. 1994, 37, 1466-1472.
50. (c) Leeson, P. D.; Carling, T. W.; Moore, K. W.; Moseley, A. M.; Smith, J. D.; Stevenson, G.; Chan, T.; Baker, R.; Foster, A. C.; Grimwood, S.; Kemp, J. A.; Marschall, G. R.; Hoogsteen, K. J. Med. Chem. 1992, 35, 1954-1968.
51. For selected examples of biologically active 2H-1-benzopyrans, see: (d) Iwasaki, T.; Mihara, S.-I.; Shimamura, T.; Kawakami, M.; Masui, M.; Hayasaki-Kajiwara, Y.; Naya, N.; Ninomiya, M.; Fujimoto, M.; Nakajima, M. J. Cardiovasc. Pharmacol. 2001, 37, 471-482.
52. (e) Mannhold, R.; Cruciani, G.; Weber, H.; Lemoine, H.; Derix, A.; Weichel, C.; Clementi, M. J. Med. Chem. 1999, 42, 981-991.
53. (f) Tronchet, J. M. J.; Zerelli, S.; Bernardinelli, G. J. Carbohydr. Chem. 1999, 18, 343-359.
54. For the methods for preparation of 2H-1-benzopyrans utilizing condensation reactions of substituted benzaldehydes or benzoic acid derivatives, see: (a) Goujon, J. Y.; Zammattio, F.; Pagnoncelli, S.; Boursereau, Y.; Kirschleger, B. Synlett 2002, 322-324.
55. (b) Wang, Q.; Finn, M. G. Org. Lett. 2000, 2, 4063-4065.
56. (c) Yavari, I.; Ramazani, A. Synth. Commun. 1997, 27, 1385-1390.
57. (d) Billeret, D.; Blondeau, D.; Sliwa, H. Synthesis 1993, 881-884.
58. For the methods for preparation of 1,2-dihydroquinolines utilizing condensation reactions of substituted benzaldehydes or benzoic acid derivatives, see: (e) Makino, K.; Hara, O.; Takiguchi, Y.; Katano, T.; Asakawa, Y.; Hatano, K.; Hamada, Y. Tetrahedron Lett. 2003, 44, 8925-8929.
59. (f) Kobayashi, K.; Nakahashi, R.; Mano, M.; Morikawa, O. Konishi, H. Bull. Chem. Soc. Jpn. 2003, 76, 1257-1259.
60. (g) Yavari, I.; Ramazani, A.; Esmaili, A. A. J. Chem. Res., Synop. 1997, 208-209.
61. (h) Kobayashi, K.; Nagato, S.; Kawakita, M.; Morikawa, O.; Konishi, H. Chem. Lett. 1995, 575-576.
62. For methods based on an electrocyclic ring closure, see: (i) Parker, K. A.; Mindt, T. L. Org. Lett. 2001, 3, 3875-3878.
63. (j) Parker, K. A.; Mindt, T. L. Org. Lett. 2002, 4, 4265-4268.
64. For the preparation 1,2-dihydroquinolines and 1,2-dihydroisoquinolines via the addition of nucleophiles to quinolinium salts, including asymmetric syntheses via additions to homochiral salts featuring a covalently attached chiral auxiliary, see: (a) Rezgui, F.; Mangeney, P.; Alexis, A. Tetrahedron Lett. 1999, 40, 6241-6244.
65. (b) Yamaguchi, R.; Tanaka, T.; Fujita, K. Chem. Commun. 1999, 2213-2214.
66. (c) Itoh, T.; Nagata, K.; Miyazaki, M.; Ohsawa, A. Synlett 1999, 1154-1156.
67. For the methods for preparation of 2H-1-benzopyrans utilizing ring-closing methathesis, see: (a) Wipf, P.; Weiner, W. S. J. Org. Chem. 1999, 64, 5321-5324.
68. (b) Grubbs, R. H.; Chang, S. J. Org. Chem. 1998, 63, 864-866.
69. (c) Hoveyda, A. H.; Harrity, J. P. A.; Wisser, J. S.; Gleason, J. D. J. Am. Chem. Soc. 1997, 119, 1488-1489.
70. For the methods for preparation of 1,2-dihydroquinolines utilizing ring-closing methathesis, see: (d) Evans, P. A.; Robinson, J. E.; Moffett, K. K. Org. Lett. 2001, 3, 3269-3271.
71. For a method utilizing palladium-catalyzed C-O bond formation, see: (e) Larock, R. C.; Wei, L.; Hightower, T. R. Synlett 1998, 522-524.
72. For the methods for preparation of 2H-1-benzopyrans and 1,2-dihydroquinolines utilizing either acid-catalyzed or transition-metal- catalyzed hydroarylation reactions, see: (a) Bigi, F.; Carloni, S.; Maggi, R.; Muchetti, C.; Sartori, G. J. Org. Chem. 1997, 62, 7024-7027.
73. (b) Pastine, S. J.; Youn, S.-W.; Sames, D. Tetrahedron 2003, 59, 8859-8868.
74. For selected examples of asymmetric synthesis of 1,2-dihydroquinolines and 2H-1-benzopyrans based on this approach, see: (a) Harrity, J. P. A.; La, D. S.; Cefalo, D. R.; Visser, M. S.; Hoveyda, A. H. J. Am. Chem. Soc. 1998, 120, 2343-2351.
75. (b) Johannes, C. W.; Visser, M. S.; Weatherhead, G. S.; Hoveyda, A. H. J. Am. Chem. Soc. 1998, 120, 8340-8347 and Reference 15a.
76. For an example of dynamic kinetic resolution of a biologically active benzopyran, see: (c) Konoike, T.; Matsumura, K.; Yorifuji, T.; Shinomoto, S.; Ide, Y.; Ohya, T. J. Org. Chem. 2002, 67, 7741-7749.
77. A catalytic asymmetric addition of a cyanide nucleophile to quinolinium salts (Reissert-type reaction) provided 1,2-dihydroquinolines in 67-96% ee; see: (a) Takamura, M.; Funabashi, K.; Shibasaki, M. J. Am. Chem. Soc. 2001, 123, 6801-6808.
78. (b) Takamura, M.; Funabashi, K.; Kanai, M. Shibasaki, M. J. Am. Chem. Soc. 2000, 122, 6327-6328.
79. Ramakrishnan, V. R.; Kagan, J. J. Org. Chem. 1970, 35, 2901-2904.
80. (a) Trepka, R. D.; Harrington, J. K.; McConville, J. W.; Kelly, T.; Mendel, A.; Pauly, D. R.; Robertson, J. E.; Waddington, J. T. J. Agric. Food Chem. 1974, 22, 1111-1119.
81. (b) Hendrickson, J. B.; Bergeron, R.; Sternbach, D. D. Tetrahedron 1975, 31, 2517-2521.
82. 3 solutions; see: Cardenas, D. J.; Mateo, C.; Echavarren, A. M. Angew. Chem., Int. Ed. Engl. 1994, 22, 2445-2447.
83. Insertion of dimethyl acetylenedicarboxylate into structurally analogous achiral azapalladacycle (see ref 21) at room temperature afforded the corresponding 1,2-dihydroquinoline in 35% yield; see: Mateo, C.; Cardenas, D. J.; Fernandez-Rivas, C.; Echavarren, A. M. Chem. Eur. J. 1996, 2, 1596-1606.
84. Depending on the spectator ligands, alkyne insertions to the known palladacycles are often limited to reactions with a highly activated dimethyl acetylenedicarboxylate; see: (a) Campora, J.; Lopez, J. A.; Palma, P.; del Rio, D.; Carmona, E.; Valerga, P.; Graiff, C.; Tiripicchio, A. Inorg. Chem. 2001, 40, 4116-4126.
85. (b) Catellani, M.; Marmiroli, B.; Chiara-Fagnola, M.; Acquotti, D. J. Organomet. Chem. 1996, 507, 157-162.
86. 3-Ni bond. See: (a) Koo, K.; Hillhouse, G. L. J. Am. Chem. Soc. 1996, 15, 2669-2671.
87. (b) Koo, K.; Hillhouse, G. L.; Rheingold, A. L. Organometallics 1995, 14, 456-460.
88. (c) Koo, K.; Hillhouse, G. L. Organometallics 1995, 14, 4421-4423.
89. (d) Campora, J.; Gutierrez, E.; Monge, A.; Palma, P.; Poveda, M. L.; Ruiz, C.; Carmona, E. Organometallics 1994, 13, 1728-1745.
90. (e) Campora, J.; Llebaria, A.; Moreto, J. M.; Poveda, M. L.; Carmona, E. Organometallics 1993, 12, 4032-4038.
91. (f) Carmona, E.; Gutierrea-Puebla, E.; Marin, J. M.; Monge, A.; Paneque, M.; Poveda, M. L.; Ruiz, C. J. Am. Chem. Soc. 1989, 111, 2883-2891.
92. 2-Pd bond with LUMO orbitals of the alkyne. See: Bennett, M. A.; Macgregor, S. A.; Wenger, E. Helv. Chim. Acta 2001, 84, 3084-3104.
93. For a discussion of the applications of vicinal diamines and specifically trans-1,2-diaminocyclohexane in asymmetric synthesis, see: (a) Lucet, D.; Le Gall, T.; Mioskowski, C. Angew. Chem., Int. Ed. 1998, 37, 2580-2627.
94. (b) Bennani, Y. L.; Hanessian, S. Chem. Rev. 1997, 97, 3161-3195.
95. Ring-closure reactions of palladium(II) iodo complexes IV (L* = L3-L6, X = O, Y = COOEt) performed under standardized conditions (t-BuOK, THF, rt, 1 h) afforded palladacycle V in 64% de from complex IV featuring ligand L3, in 50% de from complex IV with ligand L4 and in 10% de from complex IV with ligand L5. Complex IV bearing ligand L6 provided palladacycle V (X = O) as a complex mixture of several diastereomers apparently arising as a result of the creation of stereogenic palladium-bonded nitrogen atoms. For an application of ligand L6, see: Mahadevan, V.; Hou, Z.; Cole, A. P.; Root, D. E.; Solomon, E. I.; Stack, T. D. P. J. Am. Chem. Soc. 1997, 119, 11996-11997.
96. Remenar, J. F.; Brett, B. L.; Column, D. V. J. Am. Chem. Soc. 1997, 119, 5567-5572.
97. 1H NMR studies, including temperature-dependent experiments aimed at establishing the associated isomerization energy barriers are in progress and will be reported in due course.
98. 1H NMR spectroscopy; see: (a) Brown, J. M.; Perez-Torrente, J. J. Organometallics 1995, 14, 1195-1203.
99. (b) Brown, J. M.; Perez-Torrente, J. J. Organometallics 1995, 14, 207-213.
100. (c) Alster, P. L.; Boersma, J.; Smeets, W. J. J.; Spek, A. L.; van Koten, G. Organometallics 1993, 12, 1639-1647.
101. 2-Cu bond, was proposed to rationalize the observed regioselectivity of a copper-catalyzed cross-coupling reaction; see: (d) Collman, J. P.; Zhong, M.; Zhang, C.; Costanzo, S. J. Org. Chem. 2001, 66, 7892-7897.
102. 1H NMR spectroscopy; see: (e) Benedetti, M.; Saad, J. S.; Marzilli, L. G.; Natile, G. J. Chem. Soc., Dalton Trans. 2003, 872-879.
103. A restricted rotation about palladium-nitrogen bonds of two heteroarenes (2,6-diazaanthracenes) bonded to palladium centers featuring chiral nonracemic bidentate phosphine ligands gave rise to a dynamic equilibrium between diastereomeric palladium(II) complexes, and the effect of asymmetric induction on the ratio of the atropisomers was studied; see: (f) Stang, P. J.; Olenyuk, B. Angew. Chem., Int. Ed. Engl. 1996, 35, 732-736.
104. (g) Stang, P. J.; Olenuyk, B.; Arif, A. M. Organometallics 1995, 14, 5281-5289.
105. 2-N bond in atropisomeric radical intermediates. See: (a) Curran, D. P.; Liu, W.; Chen, H.-T. C. J. Am. Chem. Soc. 1999, 121, 11012-11013.
106. 2-naphthalene) complex undergoing a relatively slow interconversion of coordination diastereomers at room temperature in solutions; see: (b) Harman, W. D.; Keane, J. M.; Ding, F.; Sabat, M. J. Am. Chem. Soc. 2004, 126, 785-789.
107. 1H NMR. Thus, the silica may have effected the pH-dependent equilibrium between the atropisomers of complex (-)-13; see: (a) Coogan, M. P.; Hibbs, D. E.; Smart, E. Chem. Commun. 1999, 1991-1992.
108. However, the potential involvement of a solid-phase phenomenon known as crystallization-induced asymmetric transformation (CIAT) by which one conformer or diastereomer can be selectively trapped in the solid state as a result of crystal packing forces and other intermolecular interactions could not be rigorously ruled out; see: (b) Caddick, S.; Jenkins, K. Chem. Soc. Rev. 1996, 25, 447-456.
109. (c) Kosmrlj, J.; Weigel, L. O.; Evans, D. A.; Downey, C. W.; Wu, J. J. Am. Chem. Soc. 2003, 125, 3208-3209.
110. (d) Vedejs, E.; Donde, Y. J. Org. Chem. 2000, 65, 2337-2343.
111. Examples of processes that utilize CIAT to provide a kinetically unstable diastereomer to control the selectivity of a subsequent chemical reaction occurring with a rate faster than interconversion of the diasteomers under the reaction conditions (see ref31) are known; see: (d) Reference 31b
112. (e) Ates, A.; Curran, D. P. J. Am. Chem. Soc. 2001, 123, 5130-5131.
113. 3-hybridized carbon: a singlet at 5.16 ppm (s) for diastereomer 15b and a singlet at 4.81 ppm (s) for diastereomer 15a.
114. For a discussion of the differences in the structure and the aggregation state of enolate anions of lithium and potassium metals, in the presence of amine additives, see: (a) Smith, M. B. Organic Synthesis; McGraw-Hill: New York, 1994; Chapter 9, pp 865-869.
115. 2) rather than THF with the potassium ion. Furthermore, presence of 1 equiv of t-BuOH in reactions mediated by t-BuOK would favor the formation of solvent-separated ion pairs; see: (b) Corset, J.; Froment, F.; Lautie, M.-F.; Ratovelomanana, N.; Seyden-Penne, J.; Strzalko, T.; Roux-Schmitt, M.-C. J. Am. Chem. Soc. 1993, 115, 1684-1694.
116. 3 (24% de) and AgOTf (-22% de, excess of 15b).
117. 3-hybridized carbon: a singlet at 5.69 ppm (s) for diastereomer 16a and a singlet at 5.30 ppm (s) for diastereomer 16b.
118. The assignment is based on the assumption that the ligand exchange reaction proceeds without affecting the configurational integrity of the metal-bonded stereocenter. Stability of a Pd-C bond during a ligand exchange process has been previously established (see ref 6e), and used for the preparation of enantiomerically enriched transition metal complexes with achiral ligands; see ref 6i and Ryabov, A. D.; Panyashkina, I. M.; Polyakov, V. A.; Howard, J. A. K.; Kuzmina, L. G.; Datt, M. S.; Sacht, C. Organometallics 1998, 17, 3615-3618.
119. For an approach to the assessment of structural features of a chiral ligand via "stereocartography", see: (a) Lipkowitz, K. B.; Kozlowski, M. C. Synlett 2003, 1547-1565. The model of ligand L3 shown in Figure 5 was constructed using CS Chem3D package and energy minimization via MM2 calculations.
120. For examples of ligand exchange and geometrical isomerization reactions of palladium(II) complexes that were shown to proceed via associative pathways involving pentacoordinate palladium(II) intermediates, see: (a) Verstuyft, A. W.; Cary, L. W.; Nelson, J. H. Inorg. Chem. 1976, 15, 3161-3163.
121. (b) Verstuyft, A. W.; Nelson, J. H. Inorg. Chem. 1975, 14, 1501-1505.
122. (c) Poe, A. J.; Vaughan, D. H. Inorg. Chim. Acta 1967, 1, 255-164.
123. For the synthesis and characterization of pentacoordinate complexes of palladium(II), see: (d) Garrone, R.; Romano, A. M.; Santi, R.; Milini, R. Organometallics 1998, 17, 5419-4522.
124. (e) Albano, V. G.; Castellari, C. Organometallics 1990, 9, 1269-1276.
125. 3)PdOAc complex indicated minimum conductivity, suggesting that the complex had essentially an nonionic structure. See: (a) Yamamoto, T.; Saito, O.; Yamamoto, A. J. Am. Chem. Soc. 1981, 103, 5600-5602. In a related work, an intramolecular catalytic asymmetric arylation of an amide enolate was studied with aryl chloride, aryl bromide, and aryl iodide analogues of the substrate with the goal to establish whether the halide ligand is present on the intermediate organometallic complex in the key stereodifferentiating step. Inconclusive results were obtained indicating that both chloro and bromo analogues provided the product with similar enantioselectivity, while the iodo-analogue failed to provide products in an appreciable enantiomeric excess. See ref 4d.
126. 3 chiral shift reagent did not provide a sufficient resolution to ascertain the enantiomeric excess.
127. D +17.6 and -13.0 for complexes (+)-4 and (-)-18, respectively. For additional experiments see Supporting Information.
128. 1H NMR analysis.
129. 3.
130. 3 for (+)-8).
131. It is generally accepted that migratory insertion reactions proceed with a retention of the absolute configuration at the metal-bonded carbon; see: (a) Flood, T. C. In Topics in Inorganic and Organometallic Stereochemistry; Geoffroy, G., Allinger, N. L., Eliel, E. L., Eds.; Willey-Interscience: New York, 1981; Vol. 12, pp 37-117.
132. 2CH(D)CH(D)-t-Bu; see: (b) Bock, P. L.; Boschetto, D. J.; Rasmussen, J. R.; Demers, J. P.; Whitesides, G. M. J. Am. Chem. Soc. 1974, 96, 2814-2824.
133. 3-hybridized stereogenic carbon in an alkyne insertion reaction has been demonstrated; see: (c) Spencer, J.; Pfeffer, M. Tetrahedron: Asymmetry 1995, 6, 419-426. To date, all attempts to produce a single crystal of the high-enantiopurity (91% ee) 1,2-dihydroquinoline (+)-11a to confirm the assigned (S) configuration via a X-ray crystallographic analysis failed.
134. (a) For a light-induced racemization of 2H-1-benzopyrans, see ref 15a.
135. (b) Van Gemert, B. In Organic Photochromic and Thermochromic Compounds; Crano, J. C., Guglielmetti, R. J., Eds.; Plenum: New York, 1999; Vol. 1, Chapter 3, p 111.
136. Beholz, L. G.; Benovsky, P.; Ward, D. L.; Barta, N. S.; Stille, J. R. J. Org. Chem. 1997, 62, 1033-1042.