Asymmetric Hetero-Ene Reactions of Trimethylsilyl Enol Ethers Catalyzed by Tridentate Schiff Base Chromium(III) Complexes

Angewandte Chemie - International Edition

Volumn 42, Issue 39, 2003, Pages 4771-4774

  Ruck, Rebecca T ^a   Jacobsen, Eric N ^a  

^a HARVARD UNIVERSITY   (United States)

Author keywords

Aldehydes; Asymmetric catalysis; Chromium; Ene reaction; Schiff bases

Indexed keywords

CATALYSIS; SUBSTITUTION REACTIONS; SYNTHESIS (CHEMICAL);

CHIRAL COMPLEXES;

ETHERS;

ALDEHYDE DERIVATIVE; BETA HYDROXYSILYL ENOL ETHER DERIVATIVE; CHROMIUM DERIVATIVE; POLYOL; SCHIFF BASE; SILANE DERIVATIVE; TRIMETHYLSILYL DERIVATIVE; TRIMETHYLSILYL ENOL ETHER DERIVATIVE; UNCLASSIFIED DRUG;

ARTICLE; ASYMMETRIC CATALYSIS; CATALYSIS; CHEMICAL REACTION KINETICS; CHIRALITY; COMPLEX FORMATION; ENANTIOMER; REACTION ANALYSIS; STEREOCHEMISTRY;

ALDEHYDES; ALKYLATION; CATALYSIS; CHROMIUM; ETHERS; ORGANOSILICON COMPOUNDS; RUTHENIUM; SCHIFF BASES; STEREOISOMERISM; TRIMETHYLSILYL COMPOUNDS;

EID: 0142214760     PISSN: 14337851     EISSN: None     Source Type: Journal    
DOI: 10.1002/anie.200351591     Document Type: Article

References (16)

1. R. T. Ruck, E. N. Jacobsen, J. Am. Chem. Soc. 2002, 124, 2882-2883.
2. The hetero-Diels-Alder reactions reported using a similar catalyst also appear to proceed by a concerted mechanism: a) A. G. Dosseter, T. F. Jamison, E. N. Jacobsen, Angew. Chem. 1999, 111, 2549-2552; Angew. Chem. Int. Ed. 1999, 38, 2398-2400;
3. The hetero-Diels-Alder reactions reported using a similar catalyst also appear to proceed by a concerted mechanism: a) A. G. Dosseter, T. F. Jamison, E. N. Jacobsen, Angew. Chem. 1999, 111, 2549-2552; Angew. Chem. Int. Ed. 1999, 38, 2398-2400;
4. b) K. Gademann, D. E. Chavez, E. N. Jacobsen, Angew. Chem. 2002, 114, 3185-3187; Angew. Chem. Int. Ed. 2002, 41, 3059-3061.
5. b) K. Gademann, D. E. Chavez, E. N. Jacobsen, Angew. Chem. 2002, 114, 3185-3187; Angew. Chem. Int. Ed. 2002, 41, 3059-3061.
6. The lone previous example of an asymmetric silyl enol ether ene transformation was reported by Mikami et al. and involved reaction of 2-tert-butyldimethylsilyloxypropene and glyoxylate derivatives: K. Mikami, S. Matsukawa, M. Nagashima, H. Funabashi, H. Morishima, Tetrahedron Lett. 1997, 38, 579-582.
7. The procedure for the preparation of catalysts 1-3[1] incorporates a late-stage workup step with HCl, which is the likely source of acidic impurities.
8. B. List, P. Pojarliev, C. Castello, Org. Lett. 2001, 3, 573-576.
9. 2CHO afforded outstanding results (> 99% ee) in cycloadditions with alkoxy- or silyloxydiene derivatives. See ref. [2a], and: P. Liu, E. N. Jacobsen, J. Am. Chem. Soc. 2001,123, 10772-10773.
10. 1H NMR spectroscopy; the purified β-hydroxyketone hydrolysis products were fully characterized.
11. Separation of the products from the nonpolar catalyst was difficult and required careful chromatography. The low recovery of the silyl enol ether products is attributable to partial hydrolysis due to prolonged exposure to the chromatographic support.
12. The unprotected β-hydroxy silyl enol ethers underwent competitive elimination and/or hydrolysis reactions under a variety of Lewis acid catalyzed conditions.
13. The stereochemical assignment is tentative and based on closely related reactions: a) D. A. Evans, P. J. Coleman B. Cote J. Org. Chem. 1997, 62, 788-789;
14. b) I. Paterson, K. R. Gibson, R. M. Oballa, Tetrahedron Lett. 1996, 37, 8585-8588.
15. Electron-deficient benzaldehyde derivatives bearing ortho substituents provided the best rates and enantioselectivities in this reaction, similar to observations made in ene reactions with 2-methoxypropene. See ref. [1].
16. The relative stereochemistry was determined by hydrolysis of the product to the β-hydroxyketone and comparison of the coupling constant between the two methine protons (J = 9.3 Hz) to that of the previously reported parent phenyl analogue: S. E. Denmark, R. A. Stavenger, K.-T. Wong, Tetrahedron 1998, 54, 10389-10402.