Enantioselective formal hydration of α,β-unsaturated imides by Al-catalyzed conjugate addition of oxime nucleophiles

Journal of the American Chemical Society

Volumn 126, Issue 45, 2004, Pages 14724-14725

  Vanderwal, Christopher D ^a   Jacobsen, Eric N ^a  

^a HARVARD UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ALUMINUM; CARBOXYLIC ACID DERIVATIVE; ETHER DERIVATIVE; HYDROXYBUTYRIC ACID; IMIDE; MALIC ACID; OXIME; OXYGEN;

ARTICLE; CATALYSIS; CATALYST; ENANTIOSELECTIVITY; HYDRATION; HYDROGENOLYSIS; STEREOCHEMISTRY;

ALCOHOLS; ALKANES; ALUMINUM; CARBOXYLIC ACIDS; CATALYSIS; IMIDES; OXIMES; STEREOISOMERISM;

EID: 8844224056     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja045563f     Document Type: Article

References (22)

1. For a phosphine-catalyzed addition of water and alcohols to a variety of conjugate acceptors, see: (a) Stewart, I. C.; Bergman, R. G.; Toste, F. D. J. Am. Chem. Soc. 2003, 125, 8696-8697.
2. For a base-mediated addition of alcohols to enones, see: (b) Kisanga, P. B.; Ilankumaran, P.; Fetterly, B. M.; Verkade, J. G. J. Org. Chem. 2002, 67, 3555-3560.
3. (a) Buchanan, D. J.; Dixon, D. J.; Hernandez-Juan, F. A. Org. Lett. 2004, 6, 1357-1360.
4. (b) Adderley, N. J.; Buchanan, D. J.; Dixon, D. J.; Lainé, D. I. Angew. Chem., Int. Ed. 2003, 42, 4241-4244.
5. (c) Enders, D.; Haertwig, A.; Raabe, G.; Runsink, J. Eur. J. Org. Chem. 1998, 1771-1792.
6. Evans, D. A.; Gauchet-Prunet, J. A. J. Org. Chem. 1993, 58, 2446-2453.
7. Sekino, E.; Kumamoto, T.; Tanaka, T.; Ikeda, T.; Ishikawa, T. J. Org. Chem. 2004, 69, 2760-2767.
8. For selected examples of an alternative two-step method for this transformation involving asymmetric epoxidation of conjugate acceptors followed by reduction of the α-C-O bond, see: (a) Kakei, H.; Nemoto, T.; Ohshima, T.; Shibasaki, M. Angew. Chem., Int. Ed. 2004, 43, 317-320 and references therein.
9. (b) Corey, E. J.; Zhang, F.-Y. Org. Lett. 1999, 1, 1287-1290.
10. a range for nucleophiles that have demonstrated utility in these conjugate additions is approximately 4-12.
11. (a) Myers, J. K.; Jacobsen, E. N. J. Am. Chem. Soc. 1999, 121, 8959-8960.
12. (b) Sammis, G. M.; Jacobsen, E. N. J. Am. Chem. Soc. 2003, 125, 4442-4443.
13. (c) Taylor, M. S.; Jacobsen, E. N. J. Am. Chem. Soc. 2003, 125, 11204-11205.
14. For synthetic applications of the highly nucleophilic benzaldoximate anion, see: (a) Leung-Toung, R.; Liu, Y.; Muchowski, J. M.; Wu, Y.-L. J. Org. Chem. 1998, 63, 3235-3250.
15. (b) Gómez, V.; Pérez-Medrano, A.; Muchowski, J. M. J. Org. Chem. 1994, 59, 1219-1221.
16. Many typical organic solvents were tested, and alkane solvents proved vastly superior with respect to reaction rate. The results with cyclohexane and hexanes were comparable, while aromatic solvents led to much slower reactions. Chlorinated and ethereal solvents were poor media for the oxime addition reaction.
17. Salicylaldoxime (o-hydroxybenzaldehyde oxime) is the least expensive commercially available benzaldoxime derivative (Aldrich 2003-2004 catalogue: U.S. $36.10/100 g). For the results of a broad screen of oximes for this reaction, see the Supporting Information.
18. Substrates in which the β-substituent is aromatic, or aliphatic but much bulkier than i-Pr, suffer from competitive 1,2-addition of the oxime to both imide carbonyls. Highly insoluble substrates, such as those containing carbamate- or phthalimide-protected primary amines, also proved unreactive.
19. To assess the intrinsic diastereofacial selectivities of these substrates, we performed the addition reactions using an achiral variant of the (salen)Al catalyst derived from ethylenediamine; however, this catalyst preferentially promoted the 1,2-addition of the oxime nucleophile to the imide carbonyls. Analysis of the crude reaction mixtures indicated that a small amount of the desired conjugate addition products were formed in roughly equimolar quantities with substrates 5, 7, and 9. An important feature of these catalyst-controlled diastereoselective applications is the lack of intrinsic facial bias of the substrates. The preparation of analogous products by diastereoselective acetate aldol chemistry would likely be subject to relatively high intrinsic facial selectivities that might be difficult to override. Substrates 5, 7, and 9 were chosen to be representative of the most typically encountered motifs in polyketide chemistry, the area for which this method is most likely best suited.
20. 1H NMR): 6a (84%), 6b (81%), 8a (92%), 8b (92%), 10a (75%), 10b (83%).
21. See Supporting Information for details.
22. Attempted ethanolysis of product 4f was complicated by partial competitive desilylation. This product could be converted to the corresponding Weinreb amide in 88% yield. See Supporting Information for details. This useful transformation should be applicable to the other β-hydroxy imide products.