Weak Brønsted acid-thiourea co-catalysis: Enantioselective, catalytic protio-pictet-spengler reactions

Organic Letters

Volumn 11, Issue 4, 2009, Pages 887-890

  Klausen, Rebekka S ^a   Jacobsen, Eric N ^a  

^a HARVARD UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

BENZALDEHYDE DERIVATIVE; BENZOIC ACID; CARBOLINE DERIVATIVE; DRUG DERIVATIVE; IMINE; INDOLE ALKALOID; THIOUREA; TRYPTAMINE DERIVATIVE;

ARTICLE; CATALYSIS; CHEMICAL STRUCTURE; CHEMISTRY; CYCLIZATION; STEREOISOMERISM; SYNTHESIS;

BENZALDEHYDES; BENZOIC ACID; CARBOLINES; CATALYSIS; CYCLIZATION; IMINES; INDOLE ALKALOIDS; MOLECULAR STRUCTURE; STEREOISOMERISM; THIOUREA; TRYPTAMINES;

EID: 62749185586     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol802887h     Document Type: Article

References (23)

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4. For examples of diastereoselective Pictet-Spengler reactions of tryptophan derivatives and applications to total synthesis, see: (a) Zhou, H.; Liao, X.; Cook, J. M. Org. Lett. 2004, 6, 249-252, and references therein. For an example of a diastereoselective Pictet-Spengler reaction of a tryptamine and a chiral aldehyde, see:
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6. (c) For a complete list of methods for the preparation of enantioenriched tetrahydro-β-carbolines, see the Supporting Information.
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11. 2BCl) promote Pictet-Spengler reactions of N-β- hydroxytryptamines. Yamada, H.; Kawate, T.; Matsumizu, M.; Nishida, A.; Yamaguchi, K.; Nakagwawa, M. J. Org. Chem. 1998, 63, 6348-6354.
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16. For an example of a nonstereoselective application of this principle employing mandelic acid and achiral thiourea in the catalytic alcoholysis of styrene oxides, see: Weil, T.; Kotke, M.; Kleiner, C. M.; Schreiner, P. R. Org. Lett. 2008, 10, 1513-1516.
17. Four substrates: 44-86% ee. Taylor, M. S. Dissertation, Harvard University, 2005.
18. Examples of methoxy-and hydroxy-substituted indole alkaloids include reserpine, tubulosine, and the eudimistin family of natural products. Osorio, E. J.; Robledo, S. M.; Bastida, J. The Alkaloids, 1st ed.; Cordell, G. A., Ed.; Academic Press: San Diego, CA, 2008; Vol. 66, Chapter 2, pp 149-159.
19. The catalysts shown in Scheme 2are available from Sigma-Aldrich.
20. Catalysts analogous to 4a were first developed in the context of enantioselective Mannich-type reactions. Wenzel, A. G.; Lalonde, M. P.; Jacobsen, E. N. Synlett., 2003, 12, 1919-1922.
21. Catalyst 7a promotes enantioselective allylation of acyl hydrazones. Tan, K. L.; Jacobsen, E. N. Angew. Chem., Int. Ed. 2007, 46, 1315-1317.
22. For a complete description of catalyst screening and reaction optimization, see the Supporting Information.
23. Stronger acids, such as hydrogen chloride and methanesulfonic acid, provided product in low yield and ee, potentially due to catalyst inhibition due to protonation of the Lewis basic product.