The palladium-catalyzed aerobic kinetic resolution of secondary alcohols: Reaction development, scope, and applications

Chemistry - A European Journal

Volumn 15, Issue 47, 2009, Pages 12978-12992

  Ebner, David C ^a   Bagdanoff, Jeffrey T ^a   Ferreira, Eric M ^a   McFadden, Ryan M ^a   Caspi, Daniel D ^a   Trend, Raissa M ^a   Stoltz, Brian M ^a  

^a California Institute of Technology   (United States)

Author keywords

Alcohols; Asymmetric catalysis; Oxidation; Palladium; Synthetic methods

Indexed keywords

AMBIENT AIR; ASYMMETRIC CATALYSIS; BENZYLIC; CATALYST SYSTEM; CESIUM CARBONATES; CHIRAL LIGAND; CYCLOPROPYL; DESYM-METRIZATION; ENANTIOMERIC EXCESS; ENANTIOSELECTIVE OXIDATION; HIGH YIELD; HYDROGEN-BOND DONORS; KINETIC RESOLUTION; MESO-DIOLS; ORIGINAL SYSTEMS; RAPID RESOLUTION; REACTION CONDITIONS; SECONDARY ALCOHOLS; STOICHIOMETRIC OXIDANT; SYNTHETIC METHODS; TERMINAL OXIDANTS; TERT-BUTYL ALCOHOLS;

ALCOHOLS; CATALYSIS; CESIUM; KETONES; MOLECULAR OXYGEN; ORGANIC SOLVENTS; OXIDANTS; OXIDATION; PALLADIUM; REACTION RATES;

CATALYST SELECTIVITY;

LIGAND; ORGANOMETALLIC COMPOUND; PALLADIUM; TERT BUTYL ALCOHOL;

ARTICLE; CATALYSIS; CHEMICAL STRUCTURE; CHEMISTRY; HYDROGEN BOND; KINETICS; STEREOISOMERISM;

CATALYSIS; HYDROGEN BONDING; KINETICS; LIGANDS; MODELS, MOLECULAR; ORGANOMETALLIC COMPOUNDS; PALLADIUM; STEREOISOMERISM; TERT-BUTYL ALCOHOL;

EID: 73349131689     PISSN: 09476539     EISSN: 15213765     Source Type: Journal    
DOI: 10.1002/chem.200902172     Document Type: Article

References (177)

1. a) M. Hudlicky, Oxidations in Organic Chemistry, ACS Monograph Series, ACS, Washington, 1990;
2. T. T. Tidwell, Org. React. 1990, 39, 297-572;
3. Comprehensive Organic Synthesis (Eds.: B. M. Trost, I. Fleming), Pergamon, Oxford, 1991;
4. F. A. Luzzio, Org. React. 1998, 53, 1-221.
5. R. C. Larock, Comprehensive Organic Transformations, Wiley, New York, 1999, pp. 1234-1248.
6. a) K. Ohkubo, K. Hirata, K. Yoshinaga, M. Okada, Chem. Lett. 1976, 183-184;
7. C. Berti, M. J. Perkins, Angew. Chem. 1979, 91, 923-924;
8. Angew. Chem. Int. Ed. Engl. 1979, 18, 864-865;
9. Y. Ishii, K. Suzuki, T. Ikariya, M. Saburi, S. Yoshikawa, J. Org. Chem. 1986, 51, 2822-2824;
10. Z. Ma, Q. Huang, J. M. Bobbitt, J. Org. Chem. 1993, 58, 4837-4843;
11. S. D. Rychnovsky, T. L. McLernon, H. Rajapakse, J. Org. Chem. 1996, 61, 1194-1195;
12. Y. Kashiwagi, Y. Yanagisawa, F. Kurashima, J.-i. Anzai, T. Osa, J. M. Bobbitt, Chem. Commun. 1996, 2745-2746;
13. S. Hashiguchi, A. Fujii, K.-J. Haack, K. Matsumura, T. Ikariya, R. Noyori, Angew. Chem. 1997, 109, 300-303;
14. Angew. Chem. Int. Ed. Engl. 1997, 36, 288-290;
15. T. Hamada, R. Irie, J. Mihara, K. Hamachi, T. Katsuki, Tetrahedron 1998, 54, 10017-10028;
16. Y. Nishibayashi, I. Takei, S. Uemura, M. Hidai, Organometallics 1999, 18, 2291-2293;
17. Z. Gross, S. Ini, Org. Lett. 1999, 1, 2077-2080;
18. Y. Kashiwagi, F. Kurashima, C. Kikuchi, J.-i. Anzai, T. Osa, J. M. Bobbitt, Tetrahedron Lett. 1999, 40, 6469-6472;
19. K. Masutani, T. Uchida, R. Irie, T. Katsuki, Tetrahedron Lett. 2000, 41, 5119-5123;
20. M. Kuroboshi, H. Yoshihisa, M. N. Cortona, Y. Kawakami, Z. Gao, H. Tanaka, Tetrahedron Lett. 2000, 41, 8131-8135.
21. Subsequent to our initial report in this area, a number of further studies were reported, see: a) H. Shimizu, K. Nakata, T. Katsuki, Chem. Lett. 2002, 1080-1081;
22. W. Sun, H. Wang, C. Xia, J. Li, P. Zhao, Angew. Chem. 2003, 115, 1072-1074;
23. Angew. Chem. Int. Ed. 2003, 42, 1042-1044;
24. Y. Nishibayashi, A. Yamauchi, G. Onodera, S. Uemura, J. Org. Chem. 2003, 68, 5875-5880;
25. B. Graetz, S. Rychnovsky, W.-H. Leu, P. Farmer, R. Lin, Tetrahedron: Asymmetry 2005, 16, 3584-3598;
26. A. T. Radosevich, C. Musich, F. D. Toste, J. Am. Chem. Soc. 2005, 127, 1090-1091;
27. Z. Li, Z. H. Tang, X. X. Hu, C. G. Xia, Chem. Eur. J. 2005, 11, 1210-1216;
28. S.-S. Weng, M.-W. Shen, J.-Q. Kao, Y. S. Munot, C.-T. Chen, Proc. Natl. Acad. Sci. USA 2006, 103, 3522-3527;
29. V. D. Pawar, S. Bettigeri, S.-S. Weng, J.-Q. Kao, C.-T. Chen, J. Am. Chem. Soc. 2006, 128, 6308-6309;
30. Y.-Y. Li, X.-Q. Zhang, Z.-R. Dong, W.-Y. Shen, G. Chen, J.-X. Gao, Org. Lett. 2006, 8, 5565-5567;
31. W. Sun, X. Wu, C. Xia, Helv. Chim. Acta 2007, 90, 623-626;
32. T. Chen, J.-J. Jiang, Q. Xu, M. Shi, Org. Lett. 2007, 9, 865-868;
33. M. L. Kantam, T. Ramani, L. Chakrapani, B. M. Choudary, J. Mol. Catal. A 2007, 274, 11-15;
34. R. I. Kureshy, I. Ahmad, K. Pathak, N.-u. H. Khan, S. H. R. Abdi, J. K. Prathap, R. V. Jasra, Chirality 2007, 19, 352-357;
35. Y. Nakamura, H. Egami, K. Matsumoto, T. Uchida, T. Katsuki, Tetrahedron 2007, 63, 6383-6387;
36. K. Pathak, I. Ahmad, S. H. R. Abdi, R. I. Kureshy, N.-u. H. Khan, R. V. Jasra, J. Mol. Catal. A 2007, 274, 120-126;
37. O. Onomura, H. Arimoto, Y. Matsumura, Y. Demizu, Tetrahedron Lett. 2007, 48, 8668-8672;
38. S. Arita, T. Koike, Y. Kayaki, T. Ikariya, Angew. Chem. 2008, 120, 2481-2483;
39. Angew. Chem. Int. Ed. 2008, 47, 2447-2449;
40. M. Tomizawa, M. Shibuya, Y. Iwabuchi, Org. Lett. 2009, 11, 1829-1831.
41. B. M. Stoltz, Chem. Lett. 2004, 33, 362-367.
42. a) R. A. Johnson, K. B. Sharpless in Catalytic Asymmetric Synthesis, 2nd ed. (Ed.: I. Ojima), Wiley, New York, 2000, Chapter 6A, pp. 231-280;
43. X. Wen, I. Ojima in Catalytic Asymmetric Synthesis, 2nd ed. (Ed.: I. Ojima), Wiley, New York, 2000, Chapter 6A, pp. 281-286;
44. T. Katsuki in Catalytic Asymmetric Synthesis, 2nd ed. (Ed.: I. Ojima), Wiley, New York, 2000, Chapter 6B, pp. 287-326;
45. H. B. Kagan in Catalytic Asymmetric Synthesis, 2nd ed. (Ed.: I. Ojima), Wiley, New York, 2000, Chapter 6C, pp. 327-356;
46. R. A. Johnson, K. B. Sharpless in Catalytic Asymmetric Synthesis, 2nd ed. (Ed.: I. Ojima), Wiley, New York, 2000, Chapter 6D, pp. 357-398;
47. C. Bolm, J. P. Hildebrand, K. Muñiz in Catalytic Asymmetric Synthesis, 2nd ed. (Ed.: I. Ojima), Wiley, New York, 2000, Chapter 6E, pp. 399-428;
48. Asymmetric Oxidation Reactions (Ed.: T. Katsuki), Oxford Press, New York, 2001.
49. J. T. Mohr, D. C. Ebner, B. M. Stoltz, Org. Biomol. Chem. 2007, 5, 3571-3576.
50. For discussions on kinetic resolution, see: a) H. B. Kagan, J. C. Fiaud, in Topics in Stereochemistry, Vol. 18 (Ed.: E. L. Eliel), Wiley, New York, 1988, pp. 249-330;
51. J. M. Keith, J. F. Larrow, E. N. Jacobsen, Adv. Synth. Catal. 2001, 343, 5-26;
52. E. Vedejs, M. Jure, Angew. Chem. 2005, 117, 4040-4069;
53. Angew. Chem. Int. Ed. 2005, 44, 3974-4001.
54. a) B. M. Trost, D. L. Van Vranken, Chem. Rev. 1996, 96, 395-422;
55. M. Sodeoka, M. Shibasaki, Pure Appl. Chem. 1998, 70, 411-414;
56. T. Hayashi, J. Organomet. Chem. 1999, 576, 195-202;
57. G. Helmchen, J. Organomet. Chem. 1999, 576, 203-214;
58. B. M. Trost, Chem. Pharm. Bull. 2002, 50, 1-14;
59. T. V. RajanBabu, Chem. Rev. 2003, 103, 2845-2860;
60. T. Graening, H.-G. Schmalz, Angew. Chem. 2003, 115, 2684-2688;
61. Angew. Chem. Int. Ed. 2003, 42, 2580-2584;
62. A. B. Dounay, L. E. Overman, Chem. Rev. 2003, 103, 2945-2963;
63. L. F. Tietze, H. Ila, H. P. Bell, Chem. Rev. 2004, 104, 3453-3516;
64. B. M. Trost, J. Org. Chem. 2004, 69, 5813-5837;
65. M. Sodeoka, Y. Hamashima, Bull. Chem. Soc. Jpn. 2005, 78, 941-956;
66. K. K. Hii, Pure Appl. Chem. 2006, 78, 341-349;
67. M. Sodeoka, Y. Hamashima, Pure Appl. Chem. 2006, 78, 477-494;
68. Y. Hamashima, M. Sodeoka, Synlett., 2006, 1467-1478.
69. a) W. G. Lloyd, J. Org. Chem. 1967, 32, 2816-2819;
70. T. F. Blackburn, J. Schwartz, J. Chem. Soc. Chem. Commun. 1977, 157-158;
71. E. Gómez-Bengoa, P. Noheda, A. M. Echavarren, Tetrahedron Lett. 1994, 35, 7097-7098;
72. S. Aït-Mohand, F. Hénin, J. Muzart, Tetrahedron Lett. 1995, 36, 2473-2476;
73. K. P. Peterson, R. C. Larock, J. Org. Chem. 1998, 63, 3185-3189;
74. G.-J. ten Brink, I. W. C. E. Arends, R. A. Sheldon, Science 2000, 287, 1636-1639;
75. K. Hallman, C. Moberg, Adv. Synth. Catal. 2001, 343, 260-263;
76. R. A. Sheldon, I. W. C. E. Arends, G.-J. ten Brink, A. Dijksman, Acc. Chem. Res. 2002, 35, 774-781;
77. M. J. Schultz, C. C. Park, M. S. Sigman, Chem. Commun. 2002, 3034-3035;
78. G.-J. ten Brink, I. W. C. E. Arends, M. Hoogenraad, G. Verspui, R. A. Sheldon, Adv. Synth. Catal. 2003, 345, 497-505;
79. D. R. Jensen, M. J. Schultz, J. A. Mueller, M. S. Sigman, Angew. Chem. 2003, 115, 3940-3943;
80. Angew. Chem. Int. Ed. 2003, 42, 3810-3813;
81. G.-J. ten Brink, I. W. C. E. Arends, M. Hoogenraad, G. Verspui, R. A. Sheldon, Adv. Synth. Catal. 2003, 345, 1341-1352;
82. S. Paavola, K. Zetterberg, T. Privalov, I. Csöregh, C. Moberg, Adv. Synth. Catal. 2004, 346, 237-244;
83. T. Iwasawa, M. Tokunaga, Y. Obora, Y. Tsuji, J. Am. Chem. Soc. 2004, 126, 6554-6555.
84. For reviews of palladium-catalyzed aerobic oxidations, see: a) J. Muzart, Tetrahedron 2003, 59, 5789-5816;
85. S. S. Stahl, Angew. Chem. 2004, 116, 3480-3501;
86. Angew. Chem. Int. Ed. 2004, 43, 3400-3420;
87. M. S. Sigman, M. J. Schultz, Org. Biomol. Chem. 2004, 2, 2551-2554;
88. Reference [5].
89. a) T. Nishimura, T. Onoue, K. Ohe, S. Uemura, Tetrahedron Lett. 1998, 39, 6011-6014;
90. T. Nishimura, T. Onoue, K. Ohe, S. Uemura, J. Org. Chem. 1999, 64, 6750-6755;
91. T. Nishimura, Y. Maeda, N. Kakiuchi, S. Uemura, J. Chem. Soc. Perkin Trans. 1 2000, 4301-4305;
92. T. Nishimura, S. Uemura, Synlett., 2004, 201-216.
93. a) B. A. Steinhoff, S. S. Stahl, Org. Lett. 2002, 4, 4179-4181;
94. B. A. Steinhoff, I. A. Guzei, S. S. Stahl, J. Am. Chem. Soc. 2004, 126, 11268-11278;
95. T. Privalov, C. Linde, K. Zetterberg, C. Moberg, Organometallics 2005, 24, 885-893;
96. M. J. Schultz, R. S. Adler, W. Zierkiewicz, T. Privalov, M. S. Sigman, J. Am. Chem. Soc. 2005, 127, 8499-8507;
97. B. A. Steinhoff, A. E. King, S. S. Stahl, J. Org. Chem. 2006, 71, 1861-1868.
98. For mechanistic studies of other non-enantioselective palladium-catalyzed alcohol oxidations, see: a) S. S. Stahl, J. L. Thorman, R. C. Nelson, M. A. Kozee, J. Am. Chem. Soc. 2001, 123, 7188-7189;
99. B. A. Steinhoff, S. R. Fix, S. S. Stahl, J. Am. Chem. Soc. 2002, 124, 766-767;
100. G.-J. ten Brink, I. W. C. E. Arends, R. A. Sheldon, Adv. Synth. Catal. 2002, 344, 355-369;
101. J. A. Mueller, C. P. Goller, M. S. Sigman, J. Am. Chem. Soc. 2004, 126, 9724-9734;
102. M. M. Konnick, I. A. Guzei, S. S. Stahl, J. Am. Chem. Soc. 2004, 126, 10212-10213;
103. C. R. Landis, C. M. Morales, S. S. Stahl, J. Am. Chem. Soc. 2004, 126, 16302-16303;
104. W. Zierkiewicz, T. Privalov, Organometallics 2005, 24, 6019-6028;
105. I. W. C. E. Arends, G.-J. ten Brink, R. A. Sheldon, J. Mol. Catal. A 2006, 251, 246-254;
106. B. A. Steinhoff, S. S. Stahl, J. Am. Chem. Soc. 2006, 128, 4348-4355;
107. R. J. Nielsen, W. A. Goddard III, J. Am. Chem. Soc. 2006, 128, 9651-9660.
108. For enantioselective palladium-catalyzed alcohol oxidation mechanistic studies, see: a) J. A. Mueller, D. R. Jensen, M. S. Sigman, J. Am. Chem. Soc. 2002, 124, 8202-8203;
109. J. A. Mueller, M. S. Sigman, J. Am. Chem. Soc. 2003, 125, 7005-7013;
110. R. M. Trend, B. M. Stoltz, J. Am. Chem. Soc. 2004, 126, 4482-4483;
111. R. J. Nielsen, J. M. Keith, B. M. Stoltz, W. A. Goddard III, J. Am. Chem. Soc. 2004, 126, 7967-7974;
112. J. M. Keith, R. J. Nielsen, J. Oxgaard, W. A. Goddard III, J. Am. Chem. Soc. 2005, 127, 13172-13179;
113. J. A. Mueller, A. Cowell, B. D. Chandler, M. S. Sigman, J. Am. Chem. Soc. 2005, 127, 14817-14824;
114. B. V. Popp, S. S. Stahl, J. Am. Chem. Soc. 2007, 129, 4410-4422;
115. J. M. Keith, W. A. Goddard III, J. Oxgaard, J. Am. Chem. Soc. 2007, 129, 10361-10369;
116. R. M. Trend, B. M. Stolz, J. Am. Chem. Soc. 2008, 130, 15957-15966.
117. E. M. Ferreira, B. M. Stoltz, J. Am. Chem. Soc. 2001, 123, 7725-7726.
118. Concurrent with our publication, a related system was reported, see: a) D. R. Jensen, J. S. Pugsley, M. S. Sigman, J. Am. Chem. Soc. 2001, 123, 7475-7476;
119. D. R. Jensen, M. S. Sigman, Org. Lett. 2003, 5, 63-65;
120. S. K. Mandal, D. R. Jensen, J. S. Pugsley, M. S. Sigman, J. Org. Chem. 2003, 68, 4600-4603;
121. S. K. Mandal, M. S. Sigman, J. Org. Chem. 2003, 68, 7535-7537;
122. M. S. Sigman, D. R. Jensen, Acc. Chem. Res. 2006, 39, 221-229.
123. slow=ln[(1-C) (1-ee)]/ln[(1-C) (1+ee)], where C is conversion and ee is enantiomeric excess of recovered alcohol, see reference [8a].
124. Recently, a similar palladium-catalyzed system utilizing a different ligand for enantioselective alcohol oxidation has been developed, see reference [4k].
125. J. T. Bagdanoff, E. M. Ferreira, B. M. Stoltz, Org. Lett. 2003, 5, 835-837.
126. 2] with a variety of monodentate amines do not catalyze alcohol oxidation. For details, see reference [17b] and the Supporting Information.
127. The beneficial role of carbonates as exogenous bases in the kinetic resolution was subsequently reported by Sigman as well, see reference [17d].
128. A significant effect of cesium carbonate structure and particle size has been found for palladium-catalyzed aryl halide aminations in toluene, consistent with a heterogeneous process, see: C. Meyers, B. U. W. Maes, K. T. J. Loones, G. Bal, G. L. F. Lemiere, R. A. Dommisse, J. Org. Chem. 2004, 69, 6010-6017.
129. W. D. Crow, Aust. J. Chem. 1959, 12, 474-482.
130. CRC Handbook of Chemistry and Physics, 76th ed. (Eds.: D. R. Lide, H. P. R. Frederikse), Chemical Rubber Company, New York, 1995, Section 8, p. 43.
131. Addition of sparteine·HCl inhibits alcohol oxidation, see reference [15a].
132. 2]. Thus, formation of insoluble CsCl may sequester excess chloride and promote alcohol coordination. For details, see reference [15 f].
133. J. B. Lambert, Y. Zhao, R. W. Emblidge, L. A. Salvador, X. Liu, J.-H. So, E. C. Chelius, Acc. Chem. Res. 1999, 32, 183-190.
134. tert-Butyl alcohol was found to be a competent solvent for this oxidation, see reference [17c].
135. 2 displayed substantially lower reactivity and selectivity.
136. An alternate explanation involves the formation of trace amounts of CsOtBu in situ. However, reactions conducted with CsOtBu as base led to oxidation but no kinetic resolution, see Supporting Information for details.
137. Palladium carbonate complex 13 was also observed on prolonged exposure of 5 to cesium carbonate in chloroform at 23 °C.
138. Comprehensive Biological Catalysis, Vol. 1-3 (Ed.: M. Sinnott), Academic Press, San Diego, 1998.
139. For a recent review, see: M. S. Taylor, E. N. Jacobsen, Angew. Chem. 2006, 118, 1550-1573;
140. Angew. Chem. Int. Ed. 2006, 45, 1520-1543.
141. J. T. Bagdanoff, B. M. Stoltz, Angew. Chem. 2004, 116, 357-361;
142. Angew. Chem. Int. Ed. 2004, 43, 353-357.
143. Goddard has proposed that the solubilization of charged intermediates by dichloromethane may be so great as to nearly completely separate the chloride anion from the palladium complex in the β-hydride elimination transition state, improving the oxidation rate but limiting a key interaction for selectivity, see reference [15d].
144. F. Fischer, G. Pfleiderer, Z. Anorg. Allg. Chem. 1922, 124, 61-69.
145. For dielectric constant tables, see: CRC Handbook of Chemistry and Physics, 76th ed. (Eds.: D. R. Lide, H. P. R. Frederikse), Chemical Rubber Company, New York, 1995, Section 6, pp. 159-192.
146. 3 as reaction solvent.
147. For a discussion of the hydrogen bonding of chloroform and its effect on IR vibrational frequencies, see: R. D. Green, Hydrogen Bonding by C-H Groups, Wiley, New York, 1974.
148. A molecule of chloroform is also within hydrogen-bonding distance in the solid-state structure of 5. CCDC 203513 for 5 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data-request/cif.
149. While we have never experienced an accident, reactions conducted at elevated temperatures in flammable solvents should be conducted with appropriate caution in a fume hood.
150. For a brief discussion of the substrate scope of the oxidative kinetic resolution, see: B. M. Stoltz, D. C. Ebner in Handbook of C-H Transformation, Vol. 2 (Ed.: G. Dyker), Wiley-VCH, Weinheim, 2005, pp. 393-401.
151. D. D. Caspi, D. C. Ebner, J. T. Bagdanoff, B. M. Stoltz, Adv. Synth. Catal. 2004, 346, 185-189.
152. F. S. Ruel, M. P. Braun, W. S. Johnson, Organic Syntheses, Collect. Vol. X, Wiley, New York, 2004, pp. 467-471.
153. J. L. Luche, A. L. Gemal, J. Chem. Soc. Chem. Commun. 1978, 601-602.
154. D. C. Ebner, Z. Novák, B. M. Stoltz, Synlett., 2006, 3533-3539.
155. For example with conditions C, (±)-2-methylcyclopent-2-enol and (±)-2-methylcyclohex-2-enol ((±)-26) are oxidized with selectivity factors of 3.2 and 5.3, respectively.
156. Low reactivity was also observed in a related system, see: I. A. Sayyed, N. S. C. R. Kumar, A. Sudalai, Indian J. Chem. Sect. B 2005, 44, 1533-1535.
157. For palladium-catalyzed alcohol oxidation conditions that allow the resolution of some saturated alkyl alcohols, see reference [17c].
158. For recent applications of our kinetic resolution to natural product total synthesis, see: a) U. K. Tambar, D. C. Ebner, B. M. Stoltz, J. Am. Chem. Soc. 2006, 128, 11752-11753;
159. S. Krishnan, J. T. Bagdanoff, D. C. Ebner, Y. K. Ramtohul, U. K. Tambar, B. M. Stoltz, J. Am. Chem. Soc. 2008, 130, 13745-13754.
160. Related oxidative kinetic resolutions en route to pharmaceutical agents have been reported, see: a) I. S. Ali, A. Sudalai, Tetrahedron Lett. 2002, 43, 5435-5436;
161. V. V. Thakur, A. Sudalai, Indian J. Chem. Sect. B 2005, 44, 557-562.
162. a) R. M. Trend, Y. K. Ramtohul, E. M. Ferreira, B. M. Stoltz, Angew. Chem. 2003, 115, 2998-3001;
163. Angew. Chem. Int. Ed. 2003, 42, 2892-2895;
164. R. M. Trend, Y. K. Ramtohul, B. M. Stoltz, J. Am. Chem. Soc. 2005, 127, 17778-17788.
165. M. R. Rao, J. D. Faulkner, J. Nat. Prod. 2002, 65, 1201-1203.
166. For discussions on synthetic approaches based on bidirectional chain synthesis, see: a) C. S. Poss, S. L. Schreiber, Acc. Chem. Res. 1994, 27, 9-17;
167. S. L. Schreiber, M. T. Goulet, G. Schulte, J. Am. Chem. Soc. 1987, 109, 4718-4720.
168. For examples of bidirectional synthesis/terminus differentiation in natural products synthesis, see: a) T. Harada, Y. Kagamihara, S. Tanaka, K. Sakamoto, A. Oku, J. Org. Chem. 1992, 57, 1637-1639;
169. C. S. Poss, S. D. Rychnovsky, S. L. Schreiber, J. Am. Chem. Soc. 1993, 115, 3360-3361;
170. S. L. Schreiber, T. Sammakia, D. E. Uehling, J. Org. Chem. 1989, 54, 15-16;
171. N. Ikemoto, S. L. Schreiber, J. Am. Chem. Soc. 1990, 112, 9657-9659.
172. a) I. D. Reingold, L. J. DiNardo, J. Org. Chem. 1982, 47, 3544-3545;
173. I. D. Reingold, K. S. Kwong, B. E. Kahr, M. Menard, G. Cummings, J. A. Kowalski, Synth. Commun. 1993, 23, 1463-1466.
174. J.-E. Bäckvall, J.-O. Vågberg, J. Org. Chem. 1988, 53, 5695-5699.
175. C. R. Johnson, A. Golebiowski, T. K. McGill, D. H. Steensma, Tetrahedron Lett. 1991, 32, 2597-2600.
176. D. C. Ebner, R. M. Trend, C. Genet, M. J. McGrath, P. O'Brien, B. M. Stoltz, Angew. Chem. 2008, 120, 6467-6470;
177. Angew. Chem. Int. Ed. 2008, 47, 6367-6370.