Asymmetric cyanation of aldehydes, ketones, aldimines, and ketimines catalyzed by a versatile catalyst generated from cinchona alkaloid, achiral substituted 2,2′-biphenol and tetraisopropyl titanate

Chemistry - A European Journal

Volumn 15, Issue 43, 2009, Pages 11642-11659

  Wang, Jun ^a   Wang, Wentao ^a   Li, Wei ^a   Hu, Xiaolei ^a   Shen, Ke ^a   Tan, Cheng ^a   Liu, Xiaohua ^a   Feng, Xiaoming ^a  

^a China   (China)

Author keywords

Asymmetric catalysis; Cinchona alkaloid; Cyanation; Cyanohydrins; Strecker reaction

Indexed keywords

ASYMMETRIC CATALYSIS; CINCHONA ALKALOID; CYANATION; CYANOHYDRINS; STRECKER REACTION;

ALDEHYDES; AMINES; CATALYSIS; CATALYSTS; HYDROGEN; KETONES; NUCLEAR MAGNETIC RESONANCE;

CYANIDES;

EID: 70350504314     PISSN: 09476539     EISSN: 15213765     Source Type: Journal    
DOI: 10.1002/chem.200900936     Document Type: Article

References (178)

1. F. W. Winkler, Liebigs Ann. Chem. 1832, 4, 246.
2. A. Strecker, Ann. Chim. Farm. 1850, 75, 27.
3. a) K. Friedrich, K. Wallenfels in The Chemistry of the Cyano Group (Ed.: Z. Rappaport), Wiley-Interscience, New York, 1970, p. 67;
4. b) A. J. Fatiadi in Preparation and synthetic applications of cyanocompounds (Eds.: S. Patai, Z. Rappaport), Wiley-Interscience, New York, 1983, p. 1057.
5. For reviews on the asymmetric cyanation of aldehydes and ketones as well as the application of cyanohydrins, see: a) M. North, Synlett 1993, 807;
6. b)F. Effenberger, Angew. Chem. 1994, 106, 1609;
7. Angew. Chem. Int. Ed. Engl. 1994, 33, 1555;
8. c) R.J. H. Gregory, Chem. Rev 1999, 99, 3649;
9. d) M. Shibasaki, M. Kanai, K. Funabashi, Chem. Commun. 2002, 1989;
10. e) M. North, Tetrahedron: Asymmetry 2003, 14, 147;
11. f) J.-M. Brunei, I. P Holmes, Angew. Chem. 2004, 116, 2810;
12. Angew. Chem. Int. Ed. 2004, 43, 2752;
13. g) Synthesis and application of nonracemic cyanohydrins and a-amino nitriles, Tetrahedron Symposium-in Print, Vol.60 (Ed.: M. North), 2004, pp. 10383-10568;
14. h) T. R. J. Achard, L. A. Clutterbuck, M. North, Synlett 2005, 1828;
15. i) M. Kanai, N. Kato, E. Ichikawa, M. Shibasaki, Synlett 2005, 1491;
16. j)F.X. Chen, X. M. Feng, Curr. Org. Synth. 2006, 3, 11;
17. k) N. H. Khan, R. I. Kureshy, S. H. R. Abdi, S. Agrawal, R. V. Jasra, Coord. Chem. Rev. 2008, 252, 593;
18. l) M. North, D. L. Usanov, C. Young, Chem. Rev. 2008, 108, 5146;
19. m) J. Gawronski, N. Wascinska, J. Gajewy, Chem. Rev. 2008, 108, 5227.
20. For the selected asymmetric cyanation of aldehydes with TMSCN or HCN as cyanide source, see: a) M.T. Reetz, F. Kunisch, P Heitmann, Tetrahedron Lett. 1986, 27, 4721;
21. b) S. Kobayashi, Y. Tsuchiya, T. Mukaiyama, Chem. Lett. 1991, 541;
22. c) H. Nitta, D. Yu, M. Kudo, A. Mori, S. Inoue, J. Am. Chem. Soc. 1992, 114, 7969;
23. d) M. Hayashi, Y Miyamoto, T Inoue, N. Oguni, J. Org. Chem. 1993, 58, 1515;
24. e) E.J. Corey, Z. Wang, Tetrahedron Lett. 1993, 34, 4001;
25. f) Y Hamashima, D. Sawada, M. Kanai, M. Shibasaki, J. Am. Chem. Soc. 1999, 121, 2641;
26. g) Y. N. Belokon', S. Caveda-Cepas, B. Green, N. S. Ikonnikov, V. N. Khrustalev, V. S. Larichev, M. A. Moscalenko, M. North, C. Orizu, V. I. Tararov, M. Tasinazzo, G. I. Timofeeva, L. V. Yashkina, J. Am. Chem. Soc. 1999, 121, 3968;
27. h) Y. N. Belokon', M. North, T. Parsons, Org. Lett. 2000, 2, 1617;
28. i) J. S. You, H. M. Gau, M. C. K. Choi, Chem. Commun. 2000, 1963;
29. j) I. P Holmes, H. B. Kagan, Tetrahedron Lett. 2000, 41, 7453;
30. k) Y. Hamashima, D. Sawada, H. Nogami, M. Kanai, M. Shibasaki, Tetrahedron 2001, 57, 805;
31. C.-W. Chang, C.-T. Yang, C-D. Hwang, B.-J. Uang, Chem. Commun. 2002, 54;
32. m) J. Casas, C Nájera, J. M. Sansano, J. M. Saá, Org. Lett. 2002, 4, 2589;
33. n) Y Li, B. He, B. Qin, X. M. Feng, G. L. Zhang, J. Org. Chem. 2004, 69, 7910;
34. o) D. H. Ryu, E. J. Corey, J. Am. Chem. Soc. 2004, 126, 8106;
35. p) Y C Qin, L. Liu, L. Pu, Org. Lett. 2005, 7, 2381;
36. q) M. Hatano, T. Ikeno, T. Miyamoto, K. Ishihara, J. Am. Chem. Soc. 2005, 127, 10776;
37. r) Y. H. Wen, X. Huang, J. L. Huang, Y Xiong, B. Qin, X. M. Feng, Synlett 2005, 2445;
38. s) Y. N. Belokon', V. I. Maleev, M. North, D. L. Usanov, Chem. Commun. 2006, 4614;
39. t) Y N. Belokon', W. Clegg, R. W. Harrington, C. Young, M. North, Tetrahedron 2007, 63, 5287;
40. u) F. Yang, S. P. Wei, C. A. Chen, P. H. Xi, L. Yang, J. B. Lan, H. M. Gau, J. S. You, Chem. Eur. J. 2008, 14, 2223;
41. v) N. Kurono, K. Arai, M. Uemura, T. Ohkuma, Angew. Chem. 2008, 120, 6745;
42. Angew. Chem. Int. Ed. 2008, 47, 6643.
43. For the asymmetric cyanation of aldehydes and ketones with CNCOOEt as cyanide source, see: a) S. K. Tian, L. Deng, J. Am. Chem. Soc. 2001, 123, 6195;
44. b) J. Tian, N. Yamagiwa, S. Matsunaga, M. Shibasaki, Angew. Chem. 2002, 114, 3788;
45. Angew. Chem. Int. Ed. 2002, 41, 3636;
46. c) J. Tian, N. Yamagiwa, S. Matsunaga, M. Shibasaki, Org. Lett. 2003, 5, 3021;
47. d) Y. N. Belokon, A.J. Blacker, L. A. Clutterbuck, M. North, Org. Lett. 2003, 5, 4505;
48. e) Y. N. Belokon', A.J. Blacker, P. Carta, L. A. Clutterbuck, M. North, Tetrahedron 2004, 60, 10433;
49. f) N. Yamagiwa, J. Tian, S. Matsunaga, M. Shibasaki, J. Am. Chem. Soc. 2005, 127, 3413;
50. g) Y. N. Belokon', E. Ishibashi, H. Nomura, M. North, Chem. Commun. 2006, 1775;
51. h) Q. H. Li, L. Chang, X. H. Liu, X. M. Feng, Synlett 2006, 1675;
52. i) S. H. Gou, X. H. Chen, Y Xiong, X. M. Feng, J. Org. Chem. 2006, 71, 5732;
53. j) S. H. Gou, J. Wang, X. H. Liu, W. T Wang, F. X. Chen, X. M. Feng, Adv. Synth. Catal. 2007, 349, 343;
54. k) S. H. Gou, X. H. Liu, X. Zhou, X. M. Feng, Tetrahedron 2007, 63, 7935;
55. S. K. Chen, D. Peng, H. Zhou, L. W. Wang, F. X. Chen, X. M. Feng, Eur. J. Org. Chem. 2007, 639;
56. m) W. T. Wang, S. H. Gou, X. H. Liu, X. M. Feng, Synlett 2007, 2875;
57. n)Y. N. Belokon', W. Clegg, R. W. Harrington, E. Ishibashi, H. Nomura, M. North, Tetrahedron 2007, 63, 9724;
58. o) D. Peng, H. Zhou, X. H. Liu, L. W. Wang, S. K. Chen, X. M. Feng, Synlett 2007, 2448. For examples of using RCOCN (R = Ph, Me, MeO) and alkyl cyanophosphorylates as cyanide sources, see:
59. p) A. Baeza, J. Casas, C. Nájera, J. M. Sansano, J. M. Saá, Angew. Chem. 2003, 115, 3251;
60. Angew. Chem. Int. Ed. 2003, 42, 3143;
61. q) Y. Abiko, N. Yamagiwa, M. Sugita, J. Tian, S. Matsunaga, M. Shibasaki, Synlett 2004, 2434;
62. r) S. Lundgren, E. Wingstrand, M. Penhoat, C Moberg, J. Am. Chem. Soc. 2005, 127, 11592;
63. s) A. Baeza, C. Nájera, J. M. Sansano, J. M. Saá, Tetrahedron: Asymmetry 2005, 16, 2385;
64. t) A. Baeza, J. Casas, C. Nájera, J. M. Sansano, J. M. Saá, Eur. J. Org. Chem. 2006, 1949.
65. For use of acetone cyanohydrin and alkali metal cyanides as cyanide sources, see: a) T Ooi, K. Takaya, T Miura, H. Ichikawa, K. Maruoka, Synlett 2000, 1133;
66. b) T. Ooi, K. Takaya, T. Miura, H. Ichikawa, K. Maruoka, Tetrahedron 2001, 57, 867;
67. c) A. Watanabe, K. Matsumoto, Y. Shimada, T Katsuki, Tetrahedron Lett. 2004, 45, 6229;
68. d) C. Girard, H. B. Kagan, Angew. Chem. 1998, 110, 3088;
69. Angew. Chem. Int. Ed. 1998, 37, 2922;
70. e) Y N. Belokon', A. V. Gutnov, M. A. Moscalenko, L. V. Yashkina, D. E. Lesovoy, N. S. Ikonnikov, V. S. Larichev, M. North, Chem. Commun. 2002, 244;
71. f) N. H. Khan, S. Agrawal, R. I. Kureshy, S. H. R. Abdi, V. J. Mayani, R. V. Jasra, Eur. J. Org. Chem. 2006, 3175.
72. For the asymmetric cyanation of ketones, see: a) Y N. Belokon', B. Green, N. S. Ikonnikov, M. North, V. I. Tararov, Tetrahedron Lett. 1999, 40, 8147;
73. b) Y Hamashima, M. Kanai, M. Shibasaki, J. Am. Chem. Soc. 2000, 122, 7412;
74. c) Y Hamashima, M. Kanai, M. Shibasaki, Tetrahedron Lett. 2001, 42, 691;
75. d) K. Yabu, S. Masumoto, S. Yamasaki, Y Hamashima, M. Kanai, W. Du, D. P Curran, M. Shibasaki, J. Am. Chem. Soc. 2001, 123, 9908;
76. e) S. K. Tian, L. Deng, J. Am. Chem. Soc. 2001,123, 6195;
77. f) H. Deng, M. P Isler, M. L. Snapper, A. H. Hoveyda, Angew. Chem. 2002, 114, 1051;
78. Angew. Chem. Int. Ed. 2002, 41, 1009;
79. g) K. Yabu, S. Masumoto, M. Kanai, D. P Curran, M. Shibasaki, Tetrahedron Lett. 2002, 43, 2923;
80. h) S. Masumoto, M. Suzuki, M. Kanai, M. Shibasaki, Tetrahedron Lett. 2002, 43, 8647;
81. i) F. X. Chen, X. M. Feng, B. Qin, G. L. Zhang, Y Z. Jiang, Org. Lett. 2003, 5, 949;
82. j) S. K. Tian, R. Hong, L. Deng, J. Am. Chem. Soc. 2003, 125, 9900;
83. k) S. K. Tian, Y. G. Chen, J. F. Hang, L. Tang, P Mcdaid, L. Deng, Acc. Chem. Res. 2004, 37, 621;
84. l) F. X. Chen, H. Zhou, X. H. Liu, B. Qin, X. M. Feng, G. L. Zhang, Y. Z. Jiang, Chem. Eur. J. 2004, 10, 4790;
85. m) Y. C. Shen, X. M. Feng, Y. Li, G. L. Zhang, Y. Z. Jiang, Eur. J. Org. Chem. 2004, 129;
86. n) B. He, F. X. Chen, Y. Li, X. M. Feng, G. L. Zhang, Eur. J. Org. Chem. 2004, 4657;
87. o) B. He, F. X. Chen, Y. Li, X. M. Feng, G. L. Zhang, Tetrahedron Lett. 2004, 45, 5465;
88. p) M. Suzuki, N. Kato, M. Kanai, M. Shibasaki, Org. Lett. 2005, 7, 2527;
89. q) D. H. Ryu, E. J. Corey, J. Am. Chem. Soc. 2005, 127, 5384;
90. r) D. E. Fuerst, E. N. Jacobsen, J. Am. Chem. Soc. 2005, 127, 8964;
91. s) X. H. Liu, B. Qin, X. Zhou, B. He, X. M. Feng, J. Am. Chem. Soc. 2005, 127, 12224;
92. t)Y. Xiong, X. Huang, S. H. Gou, J. L. Huang, Y. H. Wen, X. M. Feng, Adv. Synth. Catal. 2006, 348, 538;
93. u) S. S. Kim, S. H. Lee, J. M. Kwak, Tetrahedron: Asymmetry 2006, 17, 1165;
94. v) S. S. Kim, Pure Appl. Chem. 2006, 78, 977;
95. w) Q. H. Li, X. H. Liu, J. Wang, K. Shen, X. M. Feng, Tetrahedron Lett. 2006, 47, 4011;
96. x) S. J. Zuend, E.N. Jacobsen, J. Am. Chem. Soc. 2007, 129, 15872;
97. y) B. Qin, X. H. Liu, J. Shi, K. Zheng, H. T Zhao, X. M. Feng, J. Org. Chem. 2007, 72, 2374;
98. z) K. Shen, X. H. Liu, Q. H. Li, X. M. Feng, Tetrahedron 2008, 64, 147;
99. aa) A. Alaaeddine, T. Roisnel, C. M. Thomas, J. F. Carpentier, Adv. Synth. Catal. 2008, 350, 731;
100. ab) M. Hatano, T. Ikeno, T. Matsumura, S. Torii, K. Ishihara, Adv. Synth. Catal. 2008, 350, 1776.
101. For reviews on the asymmetric Strecker reaction, see: a) L. Yet, Angew. Chem. 2001, 113, 900;
102. Angew. Chem. Int. Ed. 2001, 40, 875;
103. b)H. Gröger, Chem. Rev. 2003, 103, 2795;
104. c) C. Spino, Angew. Chem. 2004, 116, 1796;
105. Angew. Chem. Int. Ed. 2004, 43, 1764;
106. d) S. J. Connon, Angew. Chem. 2008, 120, 1194;
107. Angew. Chem. Int. Ed. 2008, 47, 1176.
108. For the asymmetric Strecker reaction of aldimines, see: a) M. S. Iyer, K. M. Gigstad, N. D. Namdev, M. Lipton, J. Am. Chem. Soc. 1996,118, 4910;
109. b) M. S. Sigman, E. N. Jacobsen, J. Am. Chem. Soc. 1998, 120, 4901;
110. c) M. S. Sigman, E. N. Jacobsen, J. Am. Chem. Soc. 1998, 120, 5315;
111. d) H. Ishitani, S. Komiyama, S. Kobayashi, Angew. Chem. 1998, 110, 3369;
112. Angew. Chem. Int. Ed. 1998, 37, 3186;
113. e) E. J. Corey, M. J. Grogan, Org. Lett. 1999, 1, 157;
114. f) C. A. Krueger, K. W. Kuntz, C. D. Dzierba, W. G. Wirschun, J. D. Gleason, M. L. Snapper, A. H. Hoveyda, J. Am. Chem. Soc. 1999, 121, 4284;
115. g) M. S. Sigman, P Vachal, E. N. Jacobsen, Angew. Chem. 2000,112, 1336;
116. Angew. Chem. Int. Ed. 2000, 39, 1279;
117. h) M. Takamura, Y. Hamashima, H. Usuda, M. Kanai, M. Shibasaki, Angew. Chem. 2000, 112, 1716;
118. Angew. Chem. Int. Ed. 2000, 39, 1650;
119. i) B. Liu, X. M. Feng, F. X. Chen, G. L. Zhang, X. Cui, Y Z. Jiang, Synlett 2001, 1551;
120. j) Z. G. Jiao, X. M. Feng, B. Liu, F. X. Chen, G. L. Zhang, Y. Z. Jiang, Eur. J. Org. Chem. 2003, 3818;
121. k) W. Mansawat, W. Bhanthumnavin, T. Vilaivan, Tetrahedron Lett. 2003, 44, 3805;
122. l) J. M. Keith, E. N. Jacobsen, Org. Lett. 2004, 6, 153;
123. m) S. Nakamura, N. Sato, M. Sugimoto, T. Toru, Tetrahedron: Asymmetry 2004, 15, 1513;
124. n)V. Banphavichit, W. Mansawat, W Bhanthumnavin, T. Vilaivan, Tetrahedron 2004, 60, 10559;
125. o) J. Huang, E.J. Corey, Org. Lett. 2004, 6, 5027;
126. p) T. Ooi, Y Uematsu, K. Maruoka, J. Am. Chem. Soc. 2006, 128, 2548;
127. q) M. Rueping, E. Sugiono, C. Azap, Angew. Chem. 2006, 118, 2679;
128. Angew. Chem. Int. Ed. 2006, 45, 2617;
129. r) J. Blacker, L. A. Clutterbuck, M. R. Crampton, C. Grosjean, M. North, Tetrahedron: Asymmetry 2006, 17, 1449;
130. s) S. Nakamura, H. Nakashima, H. Sugimoto, N. Shibata, T. Toru, Tetrahedron Lett. 2006, 47, 7599;
131. t) S. C. Pan, J. Zhou, B. List, Angew. Chem. 2007, 119, 3028;
132. Angew. Chem. Int. Ed. 2007, 46, 2971;
133. u) S. C. Pan, B. List, Org. Lett. 2007, 9, 1149;
134. v) Y. H. Wen, Y Xiong, L. Chang, J. L. Huang, X. H. Liu, X. M. Feng, J. Org. Chem. 2007, 72, 7715;
135. w) T. Ooi, Y. Uematsu, J. Fujimoto, K. Fukumoto, K. Maruoka, Tetrahedron Lett. 2007, 48, 1337;
136. x) M. Negru, D. Schollmeyer, H. Kunz, Angew. Chem. 2007, 119, 9500;
137. Angew. Chem. Int. Ed. 2007, 46, 9339;
138. y) S. C. Pan, B. List, Chem. Asian J. 2008, 3, 430;
139. z) S. Wünnemann, R. Fröhlich, D. Hoppe, Eur. J. Org. Chem. 2008, 684;
140. aa) Y. H. Wen, B. Gao, Y. Z. Fu, S. X. Dong, X. H. Liu, X. M. Feng, Chem. Eur. J. 2008,14, 6789.
141. For the asymmetric Strecker reaction of ketimines, see: a) P Vachal, E. N. Jacobsen, Org. Lett. 2000, 2, 867;
142. b) J. J. Byrne, M. Chavarot, P.-Y. Chavant, Y. Vallée, Tetrahedron Lett. 2000, 41, 873;
143. c) P. Vachal, E.N. Jacobsen, J. Am. Chem. Soc. 2002, 124, 10012;
144. d) S. Masumoto, H. Usuda, M. Suzuki, M. Kanai, M. Shibasaki, J. Am. Chem. Soc. 2003, 125, 5634;
145. e) N. Kato, M. Suzuki, M. Kanai, M. Shibasaki, Tetrahedron Lett. 2004, 45, 3153;
146. f) N. Kato, M. Suzuki, M. Kanai, M. Shibasaki, Tetrahedron Lett. 2004, 45, 3147;
147. g) N. Kato, T. Mita, M. Kanai, B. Themen, M. Kawano, K. Yamaguchi, H. Danjo, Y. Sci, A. Sato, S. Furusho, M. Shibasaki, J. Am. Chem. Soc. 2006, 128, 6768;
148. h) X. Huang, J. L. Huang, Y. H. Wen, X. M. Feng, Adv. Synth. Catal. 2006, 348, 2579;
149. i) J. L. Huang, X. H. Liu, Y. H. Wen, B. Qin, X. M. Feng, J. Org. Chem. 2007, 72, 204;
150. j) J. Wang, X. L. Hu, J. Jiang, S. H. Gou, X. Huang, X. H. Liu, X. M. Feng, Angew. Chem. 2007, 119, 8620;
151. Angew. Chem. Int. Ed. 2007, 46, 8468;
152. k) Z. R. Hou, J. Wang, X. H. Liu, X. M. Feng, Chem. Eur. J. 2008, 14, 4484;
153. K. Shen, X. H. Liu, Y. F. Cai, L. L. Lin, X. M. Feng, Chem. Eur. J. 2009,15, 6008.
154. For reviews on the asymmetric activation of racemic ligands, see: a) P. J. Walsh, A. E. Lurain, J. Balsells, Chem. Rev. 2003, 103, 3297;
155. b)J.W. Faller, A. R. Lavoie, J. Parr, Chem. Rev. 2003, 103, 3345;
156. c) K. Mikami, M. Yamanaka, Chem. Rev. 2003, 103, 3369;
157. d) K. Ding, H. Du, Y. Yuan, J. Long, Chem. Eur. J. 2004,10, 2872.
158. Part of the data in this article was communicated previously; see ref. [11j].
159. Isopropanol was added in one portion. Slow addition of iPrOH was unnecessary to ensure high enantioselectivity. For some discussions of the role of protic additives, see: ref. 10f, h. For selected examples using protonic additive to achieve good results, see: ref. [8f,r,s, 10fh,n,11f-k].
160. 3SnCN), acetone cyanohydrin, and acetyl cyanide (CH3COCN) were examined. Compared with TMSCN, generally much lower reactivities were observed under otherwise identical reaction conditions.
161. For reviews, see: a) Comprehensive Asymmetric Catalysis (Eds.: E.N. Jacobsen, A. Pfaltz, H. Yamamoto), Springer, Berlin, 1999;
162. b) F. Schmidt, R. T. Stemmler, J. Rudolph, C. Bolm, Chem. Soc. Rev. 2006, 35, 454. For the recent synthesis of chiral iec-diarylmethanols, see:
163. c) J. Wu, J. Ji, A. S. C. Chan, Proc. Natl. Acad. Sci. USA 2005, 102, 3570;
164. d) A. Kokura, S. Tanaka, T. Ikeno, T. Yamada, Org. Lett. 2006, 8, 3025;
165. e) M. D. Truppo, D. Pollard, P Devine, Org. Lett. 2007, 9, 335;
166. f) J. Sedelmeier, C. Bolm, J. Org. Chem. 2007, 72, 8859;
167. g) C.-T. Lee, B. H. Lipshutz, Org. Lett. 2008,10, 4187. For the recent synthesis of chiral iec-diarylmethylamines, see:
168. h) H.-F. Duan, Y.-X. Jia, L.-X. Wang, Q.-L. Zhou, Org. Lett. 2006, 8, 2567;
169. i) R. B. C. Jagt, P. Y. Toullec, D. Geerdink, J. G. Vries, B. L. Feringa, A. J. Minnaard, Angew. Chem. 2006, 118, 2855;
170. Angew. Chem. Int. Ed. 2006, 45, 2789;
171. j).Z.-Q. Wang, C.-G. Feng, M.-H. Xu, G.-Q. Lin, J. Am. Chem. Soc. 2007,129, 5336. For the synthesis of chiral fe«-diarylmethanols, see:
172. k) M. A. Fernández-Ibáñez, B. Maciá, A.J. Minnaard, B. L. Feringa, Org. Lett. 2008, 10, 4041. For the synthesis of chiral feM-diarylmethylamines, see:
173. l) J. Clayden, J. Dufour, D.M. Grainger, M. Helliwell, J. Am. Chem. Soc. 2007,129, 7488.
174. The impurity might be the silylated biphenol. The ee value of the product was determined by HPLC on Chiralcel OD-H column after converting 23a to the corresponding cyanohydrin acetate according to the reported method (S. Norsikian, I. Holmes, F. Lagasse, H. B. Kagan, Tetrahedron Lett. 2002, 43, 5715), in which cyanohydrin acetate could be isolated in pure form.
175. Although CNCOOEt was successfully used in the cyanation of aliphatic ketones, the reaction of CNCOOEt with aromatic ketones was not mentioned in Deng's report (see: ref. [8e]). In addition, Belokon' and North's attempt to employ CNCOOEt as the cyanide source in the cyanation of ketones also failed (see ref. [6d,e]).
176. When 1a/Ti/4m 1:1:1 or lb/Ti/4m 1:1:1 was used instead of 1b/Ti/ 4m 2:2:1, although the enantioselectivity was excellent (99% ee), longer reaction time (78 h) was required to complete the reaction. On the other hand, lowering the catalyst loading from 10 to 5 mol% led to a dramatic decrease in reaction rate, and 95% yield and 99% ee were obtained after 5 d.
177. 3 solution of 1b/Ti/4m 1:1:1 with acetonitrile.
178. K. Mai, G. Patil, J. Org. Chem. 1986, 51, 3545.