8-Bromocaffeine (8-BC): A New Versatile Reagent for Conversion of ­Aldoximes into Nitriles

Mohammad Navid Soltani Rad; Somayeh Behrouz; Abdo-Reza Nekoei

doi:10.1055/s-0031-129036

Synlett, Inhaltsverzeichnis

Synlett 2012; 23(8): 1191-1198
DOI: 10.1055/s-0031-129036

letter

8-Bromocaffeine (8-BC): A New Versatile Reagent for Conversion of Aldoximes into Nitriles

Mohammad Navid Soltani Rad*

Department of Chemistry, Shiraz University of Technology, Shiraz 71555-313, Iran, Fax: +98(711)7354520 eMail: soltani@sutech.ac.ir eMail: behrouz@sutech.ac.ir

,

Somayeh Behrouz*

Department of Chemistry, Shiraz University of Technology, Shiraz 71555-313, Iran, Fax: +98(711)7354520 eMail: soltani@sutech.ac.ir eMail: behrouz@sutech.ac.ir

,

Abdo-Reza Nekoei

Department of Chemistry, Shiraz University of Technology, Shiraz 71555-313, Iran, Fax: +98(711)7354520 eMail: soltani@sutech.ac.ir eMail: behrouz@sutech.ac.ir

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Abstract

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Abstract

A rapid and highly convenient synthesis of nitriles from the corresponding aldoximes using 8-bromocaffeine (8-BC) is described. In this protocol, aldoximes react with 8-BC in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and N,N-dimethylformamide (DMF) to furnish the corresponding nitriles under both microwave-assisted and/or conventional heating (reflux) conditions in short times and in good to excellent yields. This methodology is highly efficient for structurally diverse aldoximes including aliphatic, aromatic, and heteroaromatic oximes.

Key words

nitriles - oximes - synthetic methods - dehydration

Volltext

Referenzen

References and Notes
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36 8-BC [CAS Number: 10381-82-5] is commercially available; however, using freshly prepared 8-BC affords more favorable results. Fresh 8-BC can be easily prepared by using the following procedure: To a round-bottom flask (500 mL) containing freshly distilled CH₂Cl₂ (300 mL) was added caffeine (19.4 g, 0.1 mol) and NBS (35.2 g, 0.2 mol). When the solids had dissolved in solvent, water (100 mL) was added and the container was closed and stirred for 5 d. The solution was transferred into a separator funnel and solution of cold NaOH (100 mL, 2 M) was added the mixture was shaken to decolorize the mixture. The organic layer was separated, washed with water (2 × 200 mL), dried over Na₂SO₄ (30 g), filtered, and evaporated to provide pure 8-BC (26 g, ca. 100%)
37 General procedure for microwave-assisted conversion of aldoximes into nitriles by using 8-BC: Into a laboratory microwave oven equipped with a condenser, was inserted a round-bottom flask (50 mL) containing a solution of aldoxime (5 mmol), DBU (5 mmol), and 8-BC (6 mmol) in DMF (6 mL). The mixture was then irradiated at 300 W for the indicated time (Table 5). When TLC monitoring indicated no further improvement in the reaction, the crude products were suspended in CH₂Cl₂ (30 mL) and washed with H₂O (2 × 100 mL). The organic layer was dried over Na₂SO₄ (10 g) and concentrated to afford the crude product, which was purified by column chromatography on silica gel (n-hexane–EtOAc). All products were characterized by ¹H NMR, ¹³C NMR, IR, CHN and MS analysis
38 Selected spectral data: 4-(Allyloxy)-3-methoxy benzonitrile (Table 5, Entry 8): White solid; R_f = 0.47 (EtOAc–n-hexane, 1:5); mp 59–60 °C; ¹H NMR (250 MHz, CDCl₃): δ = 3.93 (s, 3 H, CH₃), 4.60 (dd, J = 1.3, 5.1 Hz, 2 H, OCH₂), 5.48 (dd, J = 1.5, 11.2 Hz, 2 H, =CH₂), 6.11–6.14 (m, 1 H, =CH), 7.01 (d, J = 8.1 Hz, 1 H, ArH), 7.13 (s, 1 H, ArH), 7.25 (d, J = 8.1 Hz, 1 H, ArH); ¹³C NMR (250 MHz, CDCl₃): δ = 54.17, 68.43, 104.51, 114.03, 115.94, 119.70, 119.93, 128.21, 134.58, 157.04, 161.37; MS: m/z (%) = 189.08 (30); Anal. Calcd for C₁₁H₁₁NO₂: C, 69.83; H, 5.86; N, 7.40. Found: C, 69.74; H, 5.94; N, 7.52. 3-(4-Methoxybenzyloxy) benzonitrile (Table 5, Entry 10): White solid; R_f = 0.31 (EtOAc–n-hexane, 1:9); mp 94–95 °C; ¹H NMR (250 MHz, CDCl₃): δ = 3.86 (s, 3 H, OCH₃), 5.30 (s, 2 H, OCH₂), 7.11 (d, J = 8.2 Hz, 2 H, ArH), 7.25–7.30 (m, 3 H, ArH), 7.39–7.46 (m, 3 H, ArH); ¹³C NMR (250 MHz, CDCl₃): δ = 51.16, 69.45, 112.86, 115.37, 118.70, 121.57, 123.97, 127.05, 128.14, 130.91, 132.28, 158.76, 162.29; MS: m/z (%) = 239.09 (36); Anal. Calcd for C₁₅H₁₃NO₂: C, 75.30; H, 5.48; N, 5.85. Found: C, 75.42; H, 5.60; N, 5.80. 2-[2-(1,3-Dioxoisoindolin-2-yl)ethoxy]benzonitrile (Table 5, Entry 15): White solid; R_f = 0.48 (EtOAc–n-hexane, 1:1); mp 148–149 °C; ¹H NMR (250 MHz, CDCl₃): δ = 4.03 (t, J = 5.9 Hz, 2 H, NCH₂), 4.22 (t, J = 5.9 Hz, 2 H, OCH₂), 6.88–6.91 (m, 2 H, aryl), 7.36–7.42 (m, 2 H, aryl), 7.58–7.63 (m, 2 H, aryl), 7.68–7.73 (m, 2 H, aryl); ¹³C NMR (250 MHz, CDCl₃): δ = 36.52, 65.19, 102.29, 112.29, 115.88, 121.31, 123.34, 131.86, 133.59, 133.76, 134.11, 159.66, 167.89; MS: m/z (%) = 292.08 (52); Anal. Calcd for C₁₇H₁₂N₂O₃: C, 69.86; H, 4.14; N, 9.58. Found: C, 69.82; H, 4.17; N, 9.63. 2-[5-(2-Methyl-4-nitro-1H-imidazol-1-yl)pentyloxy]-benzonitrile (Table 5, Entry 16): Bright yellow oil; R_f = 0.45 (EtOAc); ¹H NMR (250 MHz, CDCl₃): δ = 0.73–0.75 (m, 2 H, CH₂), 1.05 (m, 4 H, 2 × CH₂), 1.59 (s, 3 H, CH₃), 3.20 (m, 4 H, NCH₂, OCH₂), 6.16–6.19 (m, 2 H, ArH), 6.67–6.68 (m, 2 H, ArH), 7.13 (s, 1 H, C(5)-H, imidazole); ¹³C NMR (250 MHz, CDCl₃): δ = 12.42, 22.37, 27.68, 29.28, 46.51, 68.12, 100.81, 111.99, 116.02, 120.23, 132.97, 134.15, 144.42, 145.57, 159.94, 161.84; MS: m/z (%) = 314.10 (48); Anal. Calcd for C₁₆H₁₈N₄O₃: C, 61.13; H, 5.77; N, 17.82. Found: C, 61.15; H, 5.81; N, 17.79

8-Bromocaffeine (8-BC): A New Versatile Reagent for Conversion of ­Aldoximes into Nitriles

8-Bromocaffeine (8-BC): A New Versatile Reagent for Conversion of Aldoximes into Nitriles