Chiral quaternary alkylammonium ionic liquid [Pro-dabco][BF4]: as a recyclable and highly efficient organocatalyst for asymmetric Michael addition reactions

A novel series of chiral quaternary ammonium ionic liquids have been synthesized and shown to be very effective catalysts for the asymmetric Michael addition reactions of ketones and aldehydes to nitroolefins with excellent yields (up to 100%), diastereoselectivities (syn/anti = 99:1), and enantioselectivities (up to 97%). The catalytic system, an ionic liquid organocatalyst in [Bmim][BF4], could be reused five times without a significant loss in catalytic activity or stereoselectivity.

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(S)-tert-Butyl 2-(bromomethyl)pyrrolidine-1-carboxylateC10H18BrNO2[α]D20=-40.5 (c 0.80, CHCl3)Source of chirality: l-prolineAbsolute configuration: (S)

1-[(S)-tert-Butyl 2′-methyl pyrrolidine-1′-carboxylate]-4-aza-1-azoniabicyclo[2.2.2]octane bromideC16H30BrN3O2[α]D20=-12.0 (c 0.8, CH3OH)Source of chirality: l-prolineAbsolute configuration: (S)

1-[(S)-2′-Methylpyrrolidine]-4-aza-1-azoniabicyclo[2.2.2]octane bromideC11H22BrN3[α]D20=+20.5 (c 0.80, CH3OH)Source of chirality: l-prolineAbsolute configuration: (S)

1-[(S)-2′-Methylpyrrolidine]-4-aza-1-azoniabicyclo[2.2.2]octane tetrafluoroborateC11H22BF4N3[α]D20=+34.4 (c 0.80, CH3OH)Source of chirality: l-prolineAbsolute configuration: (S)

1-[(S)-2′-Methylpyrrolidine]-4-aza-1-azoniabicyclo[2.2.2]octane hexafluoro-phosphateC11H22F6N3P[α]D20=+27.6 (c 0.80, CH3OH)Source of chirality: l-prolineAbsolute configuration: (S)