Proline organocatalysis

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Proline organocatalysis is the use of proline as an organocatalyst in organic chemistry.

Some proline-catalyzed Michael reactions initially provided poor enantioselectivity. Newer modifications, such as MacMillan’s catalyst and Jorgensen's catalysts, improved the stereocontrol.[1]:5574[2]

Background

Proline catalysis was initially reported by two groups at Schering AG and Hoffmann-La Roche.[3][4][5][6] Proline's chiral structure enables enantioselective synthesis, favoring a particular enantiomer or diastereomer.[1]:5574[3][7][8][9]:47

Reactions

Proline catalysis has been reviewed.[3]

In the Hajos–Parrish–Eder–Sauer–Wiechert reaction, proline catalyses an asymmetric aldol reaction. The zwitterionic character and the H-bonding of proline in the transition state plays an important role in explaining the reaction outcome.[10][11][12][13] An enamine transition state is formed during the reaction and only one proline molecule is involved in forming the transition state.[14]

Asymmetric synthesis of the Wieland-Miescher ketone is also based on proline.[15] Addtional reactions include aldol reactions,[16][17][18][19] Mannich reaction,[20][21][22] Michael reaction,[23][24] amination,[21] α-oxyamination,[25][26] and α-halogenation.[27][28]

MacMillan’s and Jorgensen’s groups introduced modifications on the basic proline structure, achieving more enantioselective and regioselective catalysts.[27][28] These proline-derived auxiliaries and catalysts,[29] including the Enders hydrazone reaction and Corey–Itsuno reduction, have been reviewed,[30][31] as have MacMillan’s iminium catalysts,[32] Miller catalysts,[32] and CBS-oxazaborolidines.[33]

References

  1. 1.0 1.1 Lua error in package.lua at line 80: module 'strict' not found.
  2. Wang, Z. (2009). In "Comprehensive Organic Name Reactions and Reagents", page 1306, John Wiley & Sons. ISBN 0471704504, ISBN 9780471704508
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  4. Hajos, Z. G. and Parrish, D. R. (1971) German Patent DE 2102623
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  8. Berkessel, A., Groeger, H. (2005). "Asymmetric Organocatalysis". Wiley-VCH ISBN 3527305173
  9. Dalko, P.I. (editor) (2007). "Enantioselective Organocatalysis: Reactions and Experimental Procedures". John Wiley & Sons. ISBN 9783527315222
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