Catalytic enantioselective reformatsky reaction of alkyl iodoacetate with aldehydes catalyzed by chiral schiff base

Chemistry Letters

Volumn 37, Issue 12, 2008, Pages 1298-1299

  Tanaka, Takanori ^a   Hayashi, Masahiko ^a  

^a KOBE UNIVERSITY   (Japan)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 67649400836     PISSN: 03667022     EISSN: 13480715     Source Type: Journal    
DOI: 10.1246/cl.2008.1298     Document Type: Article

References (19)

1. For ketones: a) P. G. Cozzi, Angew. Chem., Int. Ed. 2006, 45, 2951.
2. b) M. Á. Fernández-Ibáñez, B. Maciá, A. J. Minnaard, B. L. Feringa, Chem. Commun. 2008, 2571.
3. For aldehydes: a) M. Á. Fernández-Ibáñez, B. Maciá, A. J. Minnaard, B. L. Feringa, Angew. Chem., Int. Ed. 2008, 47, 1317.
4. b) P. G. Cozzi, F. Benfatti, M. G. Capdevila, A. Mignogna, Chem. Commun. 2008, 3317.
5. For imines: P. G. Cozzi, Adv. Synth. Catal. 2006, 348, 2075.
6. For stoichiometric asymmetric Reformatsky reactions, see references cited in 1a.
7. a) M. Hayashi, Y. Miyamoto, T. Inoue, N. Oguni, J. Chem. Soc, Chem. Commun. 1991, 1752.
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11. a) M. Hayashi, T. Inoue, N. Oguni, J. Chem. Soc, Chem. Commun. 1994, 341.
12. b) M. Hayashi, T. Inoue, Y. Miyamoto, N. Oguni, Tetrahedron 1994, 50, 4385.
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14. d) M. Hayashi, K. Yoshimoto, N. Hirata, K. Tanaka, N. Oguni, K. Harada, A. Matsushita, Y. Kawachi, H. Sasaki, Isr. J. Chem. 2001, 41, 241.
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17. We examined a variety of chiral Schiff bases we reported in ref. 5 and 6. Among those, chiral Sehiff base 1 was the best choice. Especially, the existence of a tert-butyl group at the ortho position of a phenolic hydroxy group is essential to obtain high ee. For example, the Schiff base only absent a tert-butyl group at the ortho position of phenolic hydroxy group 1 (Other substituents are completely the same) gave only 22% ee (S) in 95% yield.
18. General procedure for catalytic enantioselectlve Reformatsky reaction: Dimethylzinc (0.28 mL, 4.0 mmol) was added to a solution of chiral Schiff base 1 (35.4 mg, 0.1 mmol) and ethyl iodoacetate (118.4 μL, 1.0 mmol) in solvent (6mL) at room temperature under argon atmosphere. After exchange of argon to oxygen diluted with argon, the solution of aldehyde (0.5 mmol) in solvent (2 mL) was added slowly. The reaction mixture was stirred under argon and oxygen atmosphere. After confirmation of the completion of the reaction by TLC analysis, the mixture was quenched by addition of i-PrOH (5mL) then 1 M HC1 (20 mL). After extraction with diethyl ether (20 mL × 3) and evaporation, the obtained residue was columned on silica gel (eluent; hexane:ethyl acetate = 5:1), the following Kugelrohr distillation afforded the product. Enantiomeric excess (ee) was determined by HPLC analysis (CHIRALCEL OD-H or CHIRALPAK AS, see Supporting Information).
19. Supporting Information is available electronically on the CSJ-Journal Web site, http://www.csj.jp/journals/chem-lett/index.html.