Amine additives greatly expand the scope of asymmetric hydrosilylation of imines

Angewandte Chemie - International Edition

Volumn 37, Issue 8, 1998, Pages 1103-1107

  Verdaguer, Xavier ^a   Lange, Udo E W ^a   Buchwald, Stephen L ^a  

^a MASSACHUSETTS INSTITUTE OF TECHNOLOGY   (United States)

Author keywords

Amines; Asymmetric catalysis; Imines; Reductions; Titanium

Indexed keywords

EID: 0032482056     PISSN: 14337851     EISSN: None     Source Type: Journal    
DOI: 10.1002/(SICI)1521-3773(19980504)37:8<1103::AID-ANIE1103>3.0.CO;2-M     Document Type: Article

References (30)

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12. Complex 1 is a crystalline, air-stable, yellow-orange solid that can be prepared from the corresponding dichloride derivative in one step: a) A. Schäfer, E. Karl, L. Zsolnai, G. Huttner, H. H. Brintzinger, J. Organomet. Chem. 1987, 328, 87-99; b) B. Chin, S. L. Buchwald, J. Org. Chem. 1996, 61, 5650-5651; c) P. M. Druce, B. M. Kingston, M. F. Lappert, T. R. Spalding, R. C. Srivastava, J. Chem. Soc. A, 1969, 2106-2110.
13. Complex 1 is a crystalline, air-stable, yellow-orange solid that can be prepared from the corresponding dichloride derivative in one step: a) A. Schäfer, E. Karl, L. Zsolnai, G. Huttner, H. H. Brintzinger, J. Organomet. Chem. 1987, 328, 87-99; b) B. Chin, S. L. Buchwald, J. Org. Chem. 1996, 61, 5650-5651; c) P. M. Druce, B. M. Kingston, M. F. Lappert, T. R. Spalding, R. C. Srivastava, J. Chem. Soc. A, 1969, 2106-2110.
14. Complex 1 is a crystalline, air-stable, yellow-orange solid that can be prepared from the corresponding dichloride derivative in one step: a) A. Schäfer, E. Karl, L. Zsolnai, G. Huttner, H. H. Brintzinger, J. Organomet. Chem. 1987, 328, 87-99; b) B. Chin, S. L. Buchwald, J. Org. Chem. 1996, 61, 5650-5651; c) P. M. Druce, B. M. Kingston, M. F. Lappert, T. R. Spalding, R. C. Srivastava, J. Chem. Soc. A, 1969, 2106-2110.
15. A higher activation rate is observed in the presence of piperidine and MeOH.
16. C. A. Willoughby, S. L. Buchwald, J. Am. Chem. Soc. 1994, 116, 11703-11714.
17. 3SnH regeneration in tin hydride catalyzed reductive cyclizations, see D. S. Hays, G. C. Fu, J. Org. Chem. 1996, 61, 4-5.
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19. b) a full equivalent of amine is required (in practice, more is employed) to drive the reaction to completion, because amine is consumed during the reaction. Therefore, we refer to the amine as a promoting agent, not as a catalyst;
20. c) Tani et al. reported that primary and secondary amines improve the enantioselectivity and efficiency of {Ir(BINAP)}-catalyzed hydrogenation of imines. No explanation for this effect is provided: K. Tani, J. Onouchi, T. Yamagata, Y. Kataoka, Chem. Lett. 1995, 955-956;
21. d) Evans et al. recently reported a case in which an achiral additive enhanced the enantioselectivity of an asymmetric C-N bond-forming process: D. A. Evans, S. G. Nelson, J. Am. Chem. Soc. 1997, 119, 6452-6453.
22. C. A. Willoughby, S. L. Buchwald, J. Am. Chem. Soc. 1994, 116, 8952-8965.
23. Burk et al. observed a similar effect in the {Rh(DuPHOS)}-catalyzed hydrogenation of (E)-and (Z)-enamides: M. J. Burk, J. E. Feaster, W. A. Nugent, R. L. Harlow, J. Am. Chem. Soc. 1993, 115, 10125-10138.
24. a) M. T. Reding, S. L. Buchwald, J. Org. Chem. 1995, 60, 7884-7890;
25. b) J. Lipowitz, S. A. Bowman, ibid. 1973, 38, 162-165;
26. c) S. W. Breeden, N. J. Lawrence, Synlett 1994, 833-835.
27. 3 = 1:4).
28. Although a decrease in the concentration of amine additive was observed, we have not quantified the extent of its conversion into a silylamine.
29. If this mechanism is operative, it would require that the product amine be liberated from the silicon polymer by exchange with primary amine.
30. Certain mechanistic similarities exist between this process and asymmetric dihydroxylation of olefins: J. S. M. Wai, I. Markó, J. S. Svendsen, M. G. Finn, E. N. Jacobsen, K. B. Sharpless, J. Am. Chem. Soc. 1989, 111, 1123-1125.