Asymmetric retro-[1,4] brook rearrangement and its stereochemical course at silicon

Angewandte Chemie - International Edition

Volumn 45, Issue 14, 2006, Pages 2235-2238

  Nakazaki, Atsuo ^a   Nakai, Takeshi ^a   Tomooka, Katsuhiko ^a  

^a TOKYO INSTITUTE OF TECHNOLOGY   (Japan)

Author keywords

Asymmetric synthesis; Chirality; Rearrangement; Silanes

Indexed keywords

NEGATIVE IONS; SILANES; STEREOCHEMISTRY; SYNTHESIS (CHEMICAL);

ALLYLOXYSILANE; ASYMMETRIC SYNTHESIS; CHIRALITY; REARRANGEMENT;

SILICON;

EID: 33745018571     PISSN: 14337851     EISSN: None     Source Type: Journal    
DOI: 10.1002/anie.200503734     Document Type: Article

References (35)

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7. For representative studies on retro-[1,2] Brook rearrangement, see: a) W. C. Still, T. L. Macdonald, J. Am. Chem. Soc. 1974, 96, 5561-5563;
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10. The structure of 3b was confirmed by conversion to the corresponding β-silyl propinaldehyde by acidic hydrolysis. The details are given in the Supporting Information.
11. A large excess of HMPA is important for high [1,4] selectivity. Indeed, a reaction with 1 equiv of HMPA provides [1,4] product 3b in 38% yield, along with [1,2] product 2b in 8% yield.
12. Coordination of an electrophile or solvent to the lithium ion might affect the reactivity of the allylic anion. Further work, including NMR and IR analyses of the intermediate, is under way to elucidate the reaction mechanism.
13. The relative configuration has not been determined.
14. For reviews of asymmetric synthesis based on silicon stereocenters, see: a) T. H. Chan, D. Wang, Chem. Rev. 1992, 92, 995-1006;
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18. intermolecular version: b) M. Oestreich, S. Rendler, Angew. Chem. 2005, 117, 1688-1691;
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20. We also attempted to form a C-C bond by the reaction of the lithium enolate with a carbon electrophile. Thus, silane 4a was treated successively with tBuLi and iodomethane to afford the expected product 8 in 65% yield (d.r. = 66:34) [Eq. (4)]. (Equation Presented)
21. The stereochemical course of the nucleophilic substitution on the silicon center has been investigated in various systems; it strongly depends on the leaving groups. a) L. H. Sommer in Stereochemistry, Mechanism and Silicon, McGraw-Hill, New York, 1965;
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23. The stereochemical course of the retro-[1,2] Brook rearrangement at a lithiated carbanion center has been investigated. For inversion of configuration at the benzylic anion, see: a) A. Wright, R. West, J. Am. Chem. Soc. 1974, 96, 3227-3232;
24. for retention of configuration at the aliphatic anion, see: b) R. J. Linderman, A. Ghannam, J. Am. Chem. Soc. 1990, 112, 2392-2398.
25. Ab initio calculations have shown that the configuration at the silicon center is retained in retro-[1,2] Brook rearrangements. Y. Wang, M. Dolg, Tetrahedron 1999, 55, 12 751-12 756.
26. K. Tomooka, A. Nakazaki, T. Nakai, J. Am. Chem. Soc. 2000, 122, 408-409.
27. Allyloxysilane (S)-1c was prepared from (S)-3-hydroxypyrrolidin-2-one in six steps. Details are given in the Supporting Information.
28. R = 11.8 min for R-isomer, 14.2 min for S-isomer. DIBAL = diisobutyl aluminium hydride [Eq. (5)]. (Equation Presented)
29. 3N in 78% yield.
30. CCDC-277991 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.
31. For the formation of Z-vinyl ether from allyl ether via the cisoid allylic anion, see: a) M. Schlosser, S. Strunk, Tetrahedron 1989, 45, 2649-2664;
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33. Wright and West have proposed pentacoordinated silicon as a reasonable intermediate for the retro-[1,2] Brook rearrangement. See reference [12a].
34. Recently, a pentaorganosilicate has been reported: E. P. A. Couzijn, M. Schakel, F. J. J. de Kanter, A. W. Ehlers, M. Lutz, A. L. Spek, K. Lammertsma, Angew. Chem. 2004, 116, 3522-3524;
35. Angew. Chem. Int. Ed. 2004, 43, 3440-3442.