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Synlett 2008(7): 1058-1060  
DOI: 10.1055/s-2008-1042915
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Novel and Versatile Access to Task-Specific Ionic Liquids Based on 1,2,3-Triazolium Salts

Sven Hanelt, Jürgen Liebscher*
Institute of Chemistry, Humboldt-University Berlin, Brook-Taylor-Str. 2, 12489 Berlin, Germany
Fax: +49(30)20937552; e-Mail: Liebscher@chemie.hu-berlin.de;
Further Information

Publication History

Received 15 January 2008
Publication Date:
17 March 2008 (online)

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Abstract

Novel task-specific ionic liquids based on 1,2,3-triazolium salts were prepared in a straightforward two-step procedure. Azides and alkynes were transformed into 1,4-disubstituted 1,2,3-triazoles by Cu-catalyzed click reaction. Subsequent alkylation afforded 1,3,4-trisubstituted 1,2,3-triazoles as ionic liquids. Useful functionalities, such as organocatalysts, fluorophors or linkers can be incorporated into the ionic liquids in this way.

Key words

ionic liquids - alkylation - heterocycles - click reaction - 1,2,3-triazolium salts

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Preparation of 3; General Procedure: The azide 1 (20 mmol) was dissolved in the appropriate solvent (50 mL) and CuI (see Table [1] ) was added. The flask was flushed with argon and the mixture was kept under argon until the workup procedure (balloon) was followed. DIPEA (see Table [1] ) and the alkyne 2 (10 mmol) were added one after the other, the latter in portions under stirring. If the alkyne was a solid or a sticky liquid, the solvent quantity of 50 mL was shared for dissolving the azide and the alkyne. After a short time an exothermic reaction started and the pace of the addition of the alkyne was adjusted accordingly. Cooling by a water-bath might be advisable. After complete addition of the alkyne stirring was continued at r.t. The mixture was diluted with CHCl3 (50 mL) and filtered. The filtrate was evaporated and the residue was purified by column chromatography (Kieselgel 60; MeOH-CHCl3, 1:19). If DMF was used as solvent, the reaction mixture was diluted with CHCl3 (250 mL), filtered and the filtrate was washed with H2O (3 × 150 mL) and dried with Na2SO4 before volatile compounds were removed under vacuum. Eventually the washing procedure had to be repeated.
Preparation of 5; General Procedure: A solution of the 1,2,3-triazole 3 (20 mL) and the alkylating reagent 4 (see Table [1] ) in anhyd MeCN (30 mL) was refluxed (see Table [1] ). All volatile compounds were removed under vacuum with a rotary evaporator leaving behind the ionic liquid as an oil or a sticky oil.
Compound 3a: 1H NMR (300.13 MHz, CDCl3): δ = 0.87 (t, J = 7.2 Hz, 3 H, CH2CH2CH2CH 3), 1.32 (sext, J = 7.4 Hz, 2 H, CH2CH2CH 2CH3), 1.58 (m, 2 H, CH2CH 2CH2CH3), 2.68 (t, J = 7.8 Hz, 2 H, CH 2CH2CH2CH3), 5.46 (s, 2 H, CH 2NNN), 7.19 (s, 1 H, CH), 7.27 (m, 5 H, Ph). 13C NMR (75.47 MHz, CDCl3): δ = 13.7 (CH2CH2CH2 CH3), 22.1 (CH2CH2 CH2CH3), 25.3 (CH2 CH2CH2CH3), 31.3 (CH2CH2CH2CH3), 53.8 (PhCH2), 120.5 (CHtriazole), 127.8 (CH o ), 128.4 (CH m ), 128.9 (CH p ), 134.8 (CPh), 148.8 (Ctriazole).
Compound 3e: [α]D 25 -80.3 (c 0.02, CHCl3). 1H NMR (300.13 MHz, CDCl3): δ = 1.96 (m, 4 H, NCbzCHCH 2CH 2), 3.48 (m, 2 H, NCbzCH2), 4.30 (m, 1 H, NCbzCH), 5.00 (m, 2 H, PhCH2NNN), 5.17 (m, 2 H, COOCH2), 5.34 (s, 1 H, NCOOCH 2Ph), 5.42 (s, 1 H, NCOOCH 2Ph), 7.23 (m, 10 H, 2 × Ph), 7.56 (s, 1 H, CHtriazole). 13C NMR (75.47 MHz, CDCl3): δ = 23.5 (NCbzCH2 CH2), 30.0 (NCbzCHCH2), 46.4 (NCbzCH2), 53.7 (PhCH2NNN), 57.9 (COOCH2), 58.7 (NCbzCH), 66.5 (PhCH2OCON), 123.3 (CHtriazole), 127.2-128.7 (CHPh), 134.2 (NNNCH2 C), 136.3 (NCOOCH2 C), 142.6 (CHCOOCH2 C), 154.2 (NCOOCH2Ph), 172.2 (CHCOOCH2).
Compound 3g: [α]D 25 -260.7 (c 0.033, CHCl3). H NMR (300.13 MHz, CDCl3): δ = 0.83 (t, J = 6.5 Hz, 3 H, CH2CH2CH2CH2CH 3), 1.27 (m, 5 H, CH2CH2CH 2CH 2CH3 + NCbzCHCHH), 1.61 (m, 3 H, NCbzCHCHHCH 2), 1.89 (m, 2 H, CH2CH 2CH2CH2CH3), 2.60 (m, 2 H, CH 2CH2CH2CH2CH3), 3.15 (m, 1 H, NCbzCHH), 3.33 (m, 1 H, NCbzCHH), 4.10 (m, 1 H, NCbzCH), 4.48 (m, 2 H, CHCH 2NNN), 5.13 (m, 2 H, PhCH 2), 6.88 (s, 0.7 H, CH triazole), 7.10 (s, 0.3 H, CH triazole), 7.31 (m, 5 H, Ph). 13C NMR (75.47 MHz, CDCl3): δ = 13.8 (CH2CH2CH2CH2 CH3), 22.2 (CH2CH2CH2 CH2CH3), 23.1 (NCbzCHCHH), 25.3 (CH2CH2CH2CH2CH3), 27.8 (CH2 CH2CH2CH2CH3), 28.9 (NCbzCHCH2 CH2), 31.1 (CH2CH2 CH2CH2CH3), 46.8 (NCbzCH2), 51.5 (CH2NNN), 57.1 (CHCH2NNN), 66.9 (PhCH2), 121.2 (CHtriazole), 127.7-128.4 (CHPh), 136.3 (CPh), 148.3 (Ctriazole), 154.5 (NCOO).
Compound 5a: 1H NMR (400.13 MHz, CD3CN): δ = 0.92 (t, J = 7.6 Hz, 3 H, CH2CH2CH2CH 3), 1.40 (sext, J = 7.4 Hz, 2 H, CH2CH2CH 2CH3), 1.65 (m, 2 H, CH2CH 2CH2CH3), 2.81 (t, J = 7.2 Hz, 2 H, CH 2CH2CH2CH3), 4.12 (s, 3 H, N+Me), 5.82 (s, 2 H, CH2NNN), 7.46 (m, 5 H, Ph), 8.70 (s, 1 H, CH). Signals at δ = 2.81 and 4.12 ppm showed a weak cross peak with each other in the NOESY spectrum. 13C NMR (100.61 MHz, CD3CN): δ = 13.5 (CH2CH2CH2 CH3), 22.2 (CH2CH2 CH2CH3), 23.4 (CH2 CH2CH2CH3), 29.0 (CH2CH2CH2CH3), 38.5 (N+Me), 57.1 (PhCH2), 117.9 (CHtriazole), 128.8 (CH o ), 129.6 (CH m ), 130.0 (CH p ), 133.0 (CPh), 145.5 (Ctriazole).
Compound 5e: [α]D 25 -36.1 (c 0.024, CHCl3). 1H NMR (300.13 MHz, CDCl3): δ = 1.87 (m, 4 H, NCbzCHCH 2CH 2), 3.40 (m, 2 H, NCbzCH2), 4.06 (s, 3 H, N+Me), 4.21 (m, 1 H, NCbzCH), 4.89 (m, 2 H, PhCH2NNN), 5.45 (m, 2 H, COOCH2), 5.34 (s, 1 H, NCOOCH2Ph), 5.42 (s, 1 H, NCOOCH2Ph), 7.27 (m, 10 H, 2 × Ph), 8.87 (s, 1 H, CHtriazole). 13C NMR (75.47 MHz, CDCl3): δ = 23.1 (NCbzCH2 CH2), 29.9 (NCbzCHCH2), 39.3 (N+Me), 46.3 (NCbzCH2), 54.2 (PhCH2NNN), 57.0 (COOCH2), 58.6 (NCbzCH), 66.5 (PhCH2OCON), 123.3 (CHtriazole), 127.0-130.6 (CHPh), 135.9 (NNNCH2 C), 138.3 (NCOOCH2 C), 142.3 (CHCOOCH2 C), 153.9 (NCOOCH2Ph), 171.5 (CHCOOCH2).
Compound 5g: [α]D 25 -72.9 (c 0.02, CHCl3). 1H NMR (300.13 MHz, CD3CN): δ = 0.87 (t, J = 6.5 Hz, 3 H, CH2CH2CH2CH2CH 3), 1.31 (m, 5 H, CH2CH2CH 2CH 2CH3 + NCbzCHCHH), 1.58 (m, 3 H, NCbzCHCHHCH 2), 1.87 (m, 2 H, CH2CH 2CH2CH2CH3), 2.39 (m, 2 H, CH 2CH2CH2CH2CH3), 3.16 (m, 1 H, NCbzCHH), 3.34 (m, 1 H, NCbzCHH), 3.90 (m, 1 H, NCbzCH), 4.07 (s, 3 H, N+Me), 4.51 (m, 2 H, CHCH 2NNN), 5.12 (m, 2 H, PhCH 2), 7.35 (m, 5 H, Ph), 8.55 (s, 1 H, CHtriazole). 13C NMR (75.47 MHz, CD3CN): δ = 14.0 (CH2CH2CH2CH2 CH3), 22.6 (CH2CH2CH2 CH2CH3), 23.5 (NCbzCHCHH), 25.7 (CH2CH2CH2CH2CH3), 27.1 (CH2 CH2CH2CH2CH3), 28.6 (NCbzCHCH2 CH2), 31.2 (CH2CH2 CH2CH2CH3), 38.3 (N+Me), 47.3 (NCbzCH2), 51.6 (CH2NNN), 57.6 (CHCH2NNN), 67.0 (PhCH2), 118.1 (CHtriazole), 128.1-129.7 (CHPh), 137.8 (CPh), 146.8 (Ctriazole), 155.6 (NCOO).