Highly enantioselective direct conjugate addition of ketones to nitroalkenes promoted by a chiral primary amine-thiourea catalyst

Journal of the American Chemical Society

Volumn 128, Issue 22, 2006, Pages 7170-7171

  Huang, Hongbing ^a   Jacobsen, Eric N ^a  

^a HARVARD UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ALKENE DERIVATIVE; AMINE; KETONE DERIVATIVE; NITRO DERIVATIVE; THIOUREA;

ADDITION REACTION; ALKYLATION; ARTICLE; CATALYST; CHIRALITY; CONJUGATION; DIASTEREOISOMER; ENANTIOSELECTIVITY; QUANTUM YIELD; REACTION ANALYSIS; STEREOCHEMISTRY;

ALKENES; AMINES; CATALYSIS; KETONES; MOLECULAR STRUCTURE; NITRO COMPOUNDS; STEREOISOMERISM; THIOUREA;

EID: 33744928626     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja0620890     Document Type: Article

References (41)

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32. Results obtained with representative catalyst structures are provided as Supporting Information.
33. To our knowledge, these represent the first examples of highly enantioselective asymmetric addition of ketones to aliphatic nitroolefins. For earlier efforts, see ref 4g.
34. Added benzoic acid leads to increased product yield, but does not affect the enantioselectivity of these reactions. Therefore, it is likely not involved in the ee-determining conjugate addition step, but rather only in minimizing byproduct formation by accelerating the delicate balance of imine and enamine formation and imine hydrolysis steps in the desired catalytic pathway. No beneficial effect of added acid was observed for certain substrate combinations (see Chart 1).
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39. Consistent with this hypothesis, cyclic ketones capable only of forming E-enamines afford syn products. See also ref 5.
40. The precise mode of nitroalkene binding to the thiourea is not known. Ground state structures determined both experimentally (Etter, M. C.; Urbanczyk-Lipkowska, Z.; Zia-Ebrahimi, M.; Panunto, T. W. J. Am. Chem. Soc. 1990, 112, 8415-8426) and computationally (Zuend, S.; Jacobsen, E. N., unpublished) point to an in-plane arrangement with each thiourea hydrogen bound to one oxygen of the nitro group as most stable. However, modeling studies suggest that an out-of-plane binding geometry, wherein only one of the nitro group oxygens is engaged by the thiourea, may be required for intramolecular reaction with the enamine.
41. For example, aldehydes participate in highly enantioselective additions to nitroalkenes with primary amine-thiourea catalysts closely related to 1: Lalonde, M. P.; Chen, Y.; Jacobsen, E. N. work in progress.