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DOI: 10.1055/s-2008-1078593
(S)-Pyrrolidin-2-ylmethyl-1,2,3-triazolium Salts - Ionic Liquid Supported Organocatalysts for Enantioselective Michael Additions to β-Nitrostyrenes
Publikationsverlauf
Publikationsdatum:
15. Juli 2008 (online)
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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.
Key words
asymmetric organocatalysis - ionic liquids - Michael addition - task-specific ionic liquids
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References and Notes
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-¹; t
R = 10.90
(minor), 15.53 min (major)]. All the Michael addition products
are known compounds.