Synlett 2008(15): 2342-2344  
DOI: 10.1055/s-2008-1078593
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

(S)-Pyrrolidin-2-ylmethyl-1,2,3-triazolium Salts - Ionic Liquid Supported Organocatalysts for Enantioselective Michael Additions to β-Nitrostyrenes

Zekarias Yacob, Jabbar Shah, Joachim Leistner, Jürgen Liebscher*
Institut für Chemie, Humboldt-Universität Berlin, Brook-Taylor-Str. 2, 12489 Berlin, Germany
Fax: +49(30)20937552; e-Mail: liebscher@chemie.hu-berlin.de;
Further Information

Publication History

Received 12 May 2008
Publication Date:
15 July 2008 (online)

Abstract

(S)-Pyrrolidin-2-ylmethyl-1,2,3-triazolium salts were synthesized as new task-specific ionic liquids via click reaction and alkylation. They serve as excellent recyclable catalysts in enantioselective Michael additions to nitrostyrenes in excess of carbonyl compounds as reactant and as solvent providing high yields and stereoselectivities.

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Typical Procedure of Michael Addition of Cyclo-hexanone to Nitrostyrene Nitrostyrene (37 mg, 0.25 mmol) and 4 (10 mol%) were mixed with cyclohexanone (0.5 mL, 5 mmol) in the presence of TFA (0.00625 mmol, 0.2 µL) at r.t. (bulk solution of TFA in cyclohexanone was freshly prepared from 5 µL TFA in 12.5 mL of cyclohexanone). After stirring for 24 h, the homogeneous reaction mixture was diluted with Et2O to precipitate the catalyst. The organic layer was separated and loaded onto a silica gel column to afford the Michael adduct (60 mg, 98%) as white solid; syn/anti = 99:1, 99% ee [by HPLC on a Chiralpak AD column, λ = 215 nm, eluent
i-PrOH-hexane (10:90), flow rate = 0.8 mL min; t R = 10.90 (minor), 15.53 min (major)]. All the Michael addition products are known compounds.