Catalytic enantioselective synthesis of quaternary stereocenters via intermolecular C-acylation of silyl ketene acetals: Dual activation of the electrophile and the nucleophile

Journal of the American Chemical Society

Volumn 125, Issue 14, 2003, Pages 4050-4051

  Mermerian, Ara H ^a   Fu, Gregory C ^a  

^a MASSACHUSETTS INSTITUTE OF TECHNOLOGY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ACID ANHYDRIDE; ACYLPYRIDINIUM; ALDEHYDE DERIVATIVE; ENOLATE; ETHER DERIVATIVE; HALIDE; KETENE DERIVATIVE; LEWIS ACID; PYRIDINIUM DERIVATIVE; SILYL KETENE ACETAL; UNCLASSIFIED DRUG;

ACYLATION; ARTICLE; CATALYSIS; CHEMICAL BOND; CHEMICAL STRUCTURE; ENANTIOSELECTIVITY; REACTION ANALYSIS; STEREOISOMERISM; STRUCTURE ANALYSIS;

ACETALS; ACETIC ANHYDRIDES; ACYLATION; CATALYSIS; ETHYLENES; KETONES; SILANES; STEREOISOMERISM;

EID: 0037427250     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja028554k     Document Type: Article

References (28)

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3. The effective use of chiral auxiliaries to achieve asymmetric acylations of enolates has been described. For pioneering work, see: (a) Evans, D. A.; Ennis, M. D.; Le, T.; Mandel, N.; Mandel, G. J. Am. Chem. Soc. 1984, 106, 1154-1156.
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12. (b) catalytic asymmetric Michael reaction: Hamashima, Y.; Hotta, D.; Sodeoka, M. J. Am. Chem Soc. 2002, 124, 11240-11241.
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19. For a recent review of catalytic asymmetric methods that generate quaternary stereocenters, see: Corey, E. J.; Guzman-Perez, A. Angew. Chem., Int. Ed. 1998, 37, 388-401. See also: Christoffers, J.; Mann, A. Angew. Chem., Int. Ed. 2001, 40, 4591-4597.
20. Gem-dimethyl substitution is present for ease of synthesis (double deprotonation of an arylacetic acid, followed by trapping with isobutylene oxide). As shown in Table 1. these groups are not necessary for high enantioselectivity.
21. (a) DMAP derivative 4 also catalyzes the C-acylation of silyl ketene acetals by reagents such as acid chlorides, albeit in lower enantiomeric excess.
22. (b) Use of isobutyric, rather than acetic, anhydride as the acylating agent for the silyl ketene acetal illustrated in Table 1, entry I, provides the desired product in 83% ee. but the reaction is quite slow.
23. (c) The enantioselectivity is not very sensitive to temperature.
24. (d) We observe none of the product derived from O-acylation of the silyl ketene acetal.
25. (e) Currently, silyl ketene acetals in which the aryl group is replaced with an alkyl or alkenyl substituent are not suitable substrates (low conversion).
26. 1H NMR studies that the minor isomer of 8 is more reactive than the major isomer.
27. 2).
28. 3).