Exploration of 4,5-dimethyl-1H-imidazole N-oxide derivatives in the synthesis of new achiral and chiral ionic liquids

New 1-alkoxy-3-alkyl-4,5-dimethylimidazolium bromides were synthesized by alkylation of the corresponding 1-alkylimidazole 3-oxides, which were conveniently prepared via condensation of α-(hydroxyimino)ketones, primary aliphatic amines, and formaldehyde. By using enantiomerically pure chiral amines, optically active imidazolium salts were obtained. Treatment with sodium tetrafluoroborate in acetone yielded the corresponding imidazolium tetrafluoroborates. All these compounds, with only one exception, were obtained as oils, which are considered as potential ionic liquids and ‘chiral ionic liquids’. The reduction of the chiral or non-chiral 1-alkylimidazole 3-oxides with Raney-Ni, followed by alkylation with alkyl bromides and subsequent ion exchange to tetrafluoroborates, gave the corresponding 1,3-dialkylimidazolium salts, most of them showing properties of ionic liquids. The alkylation of 1-butyl-4,5-dimethylimidazole 3-oxide and the corresponding imidazole, respectively, with 1,3-dibromopropane led to the first bis-imidazolium dibromides and bis-tetrafluoroborates.

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(S)-1-(2-Hydroxypropyl)-4,5-dimethyl-1H-imidazoleC8H14N2OEe = 100%[α]D20=+69.2 (c 0.2, CH2Cl2)Source of chirality: chiral substrateAbsolute configuration: (S)

Methyl (S)-2-(4,5-dimethyl-1H-imidazol-1-yl)propanoateC9H14N2O2Ee = 100%[α]D20=-9.9 (c 0.2, CH2Cl2)Source of chirality: chiral substrateAbsolute configuration: (S)

(S)-1-Butoxy-4,5-dimethyl-3-(2-hydroxypropyl)imidazolium bromideC12H23BrN2O2Ee = 100%[α]D20=+13.7 (c 0.2, CH2Cl2)Source of chirality: chiral substrateAbsolute configuration: (S)

(S)-1-Butoxy-4,5-dimethyl-3-(1-[methoxycarbonyl]ethyl)imidazolium bromideC13H23BrN2O3Ee = 100%[α]D20=+14.2 (c 0.2, CH2Cl2)Source of chirality: chiral substrateAbsolute configuration: (S)

(S)-4,5-Dimethyl-1-hexyloxy-3-(1-[methoxycarbonyl]ethyl)imidazolium bromideC15H27BrN2O3Ee = 100%[α]D20=+11.1 (c 0.2, CH2Cl2)Source of chirality: chiral substrateAbsolute configuration: (S)

(S)-1-Butoxy-4,5-dimethyl-3-(2-hydroxypropyl)imidazolium tetrafluoroborateC12H23BF4N2O2Ee = 100%[α]D20=+21.8 (c 0.2, CH2Cl2)Source of chirality: chiral substrateAbsolute configuration: (S)

(S)-1-Butoxy-4,5-dimethyl-3-(1-[methoxycarbonyl]ethyl)imidazolium tetrafluoroborateC13H23BF4N2O3Ee = 100%[α]D20=+14.7 (c 0.2, CH2Cl2)Source of chirality: chiral substrateAbsolute configuration: (S)

(S)-4,5-Dimethyl-1-hexyloxy-3-(1-[methoxycarbonyl]ethyl)imidazolium tetrafluoroborateC15H27BF4N2O3Ee = 100%[α]D20=+9.5 (c 0.2, CH2Cl2)Source of chirality: chiral substrateAbsolute configuration: (S)

(S)-3-Butyl-4,5-dimethyl-1-(2-hydroxypropyl)imidazolium bromideC12H23BrN2OEe = 100%[α]D20=+13.8 (c 0.2, CH2Cl2)Source of chirality: chiral substrateAbsolute configuration: (S)

(S)-1-Butyl-3-(1-[methoxycarbonyl]ethyl)-4,5-dimethylimidazolium bromideC13H23BrN2O2Ee = 100%[α]D20=+11.2 (c 0.2, CH2Cl2)Source of chirality: chiral substrateAbsolute configuration: (S)

(S)-1-Butyl-4,5-dimethyl-3-(2-hydroxypropyl)imidazolium tetrafluoroborateC12H23BF4N2OEe = 100%[α]D20=+21.2 (c 0.2, CH2Cl2)Source of chirality: chiral substrateAbsolute configuration: (S)

(S)-1-Butyl-4,5-dimethyl-3-(1-[methoxycarbonyl]ethyl)imidazolium tetrafluoroborateC13H23BF4N2O2Ee = 100%[α]D20=+10.3 (c 0.2, CH2Cl2)Source of chirality: chiral substrateAbsolute configuration: (S)