C2-symmetric Sc(III)-complexes as chiral Lewis acids. Catalytic enantioselective aldol additions to glyoxylate esters

Organic Letters

Volumn 4, Issue 20, 2002, Pages 3375-3378

  Evans, David A ^a   Masse, Craig E ^a   Wu, Jimmy ^a  

^a HARVARD UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

3-HYDROXYBUTANAL; ALDEHYDE; ALDOL; CATION; ESTER; GLYOXYLIC ACID DERIVATIVE; HETEROCYCLIC CARBOXYLIC ACID; SCANDIUM;

ARTICLE; CATALYSIS; CHEMICAL STRUCTURE; CHEMISTRY; CONFORMATION; STEREOISOMERISM;

ACIDS, HETEROCYCLIC; ALDEHYDES; CATALYSIS; CATIONS; ESTERS; GLYOXYLATES; MODELS, MOLECULAR; MOLECULAR CONFORMATION; MOLECULAR STRUCTURE; SCANDIUM; STEREOISOMERISM;

EID: 0037015425     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol026488l     Document Type: Article

References (14)

1. Evans, D. A.; Rovis, T.; Johnson, J. S. Pure Appl. Chem. 1999, 71, 1407-1415.
2. Evans, D. A.; Kozlowski, M. C.; Tedrow, J. S. Tetrahedron Lett. 1996, 37, 7481-7484.
3. Evans, D. A.; MacMillan, D. W. C.; Campos, K. R. J. Am. Chem. Soc. 1997, 119, 10859-10860.
4. For a comprehensive review of catalytic enantioselective aldol reactions: see Nelson, S. G. Tetrahedron: Asymmetry 1998, 9, 357-389.
5. Evans, D. A.; Sweeney, Z. K.; Rovis, T.; Tedrow, J. S. J. Am. Chem. Soc. 2001, 123, 12095-12096. For a syn-aldol, cf.: Mikami, K.; Matsukawa, S. J. Am. Chem. Soc. 1994, 116, 4077-4078.
6. Evans, D. A.; Sweeney, Z. K.; Rovis, T.; Tedrow, J. S. J. Am. Chem. Soc. 2001, 123, 12095-12096. For a syn-aldol, cf.: Mikami, K.; Matsukawa, S. J. Am. Chem. Soc. 1994, 116, 4077-4078.
7. (a) Evans, D. A.; Murry, J. A.; Kozlowski, M. C. J. Am. Chem. Soc. 1996, 118, 5814-5815.
8. (b) Evans, D. A.; Kozlowski, M. C.; Burgey, C. S.; MacMillan, D. W. C. J. Am. Chem. Soc. 1997, 119, 7893-7894.
9. 6 complexes: 1b (11% ee), 1c (50% ee), 1d (40% ee).
10. For the addition to ethyl glyoxylate catalyzed by 1a, the corresponding (E)-thiosilylketene acetals led to the formation of the malate products in lower yields and syn selectivity. For example, the reaction of (E)-2b afforded 3b (80% ee, dr 1.4:1) and (E)-2c afforded 3c (78% ee, dr 1:1).
11. The trimethylsilyl enolsilane derived from acetophenone afforded the aldol product in 11% ee using the conditions in Table 2.
12. 3 complex were input into Chem 3D Pro; the vicinal triflates were removed and replaced with chloride ions, and the remaining triflate and bound water were replaced with ethyl glyoxylate, which was docked onto the Sc-center. The ligand-Sc bond lengths were held constant and the molecular energy of the structure minimized.
13. These structures were subjected to a MM2 transition state minimization using Chem 3D Pro (Version 5.0). In each model, an apical or equatorial binding of the aldehyde carbonyl was minimized separately with the lower energy structure shown.
14. The application of this methodology to the asymmetric synthesis of pantolactone derivatives is described in the following paper in this issue.