Starting reagents were purchased from commercial sources and were used without any additional purification. 1H and 13C NMR spectra were acquired on a Jeol JNM-ECA 600 spectrometer (JEOL Ltd., Tokyo, Japan, with operating frequencies of 600 and 150 MHz, respectively) at room temperature and referenced to the residual signals of the solvent. The solvent used for NMR was CDCl3. Chemical shifts are reported in parts per million (δ/ppm). Coupling constants (J) are reported in Hertz (Hz). The peak patterns are indicated as follows: s, singlet; t, triplet; m, multiplet. Infrared spectra were measured on an Infralum FT-801 FT/IR instrument. The wavelengths are reported in reciprocal centimeters (ν max/cm−1). Mass spectra were recorded with LCMS-8040 Triple quadrupole liquid chromatograph mass spectrometer from Shimadzu (Shimadzu corp., Japan, ESI) and Kratos MS-30 mass-spectrometer (Shimadzu division, Japan, EI, 70 eV). HRMS spectra were recorded on a Bruker MicrOTOF-Q II (Bruker corp., Bremen, Germany). Elemental analysis was performed with a Euro Vector EA-3000 elemental analyzer (EuroVector S.p.A., Milan, Italy). The reaction progress was monitored by TLC and the spots were visualized under UV light (254 or 365 nm). Column chromatography was performed using silica gel (60–75 mesh). Melting points were determined on an SMP-10 apparatus and were uncorrected. Solvents were distilled and dried according to standard procedures.
4.2. 1-Benzyl-2-(thien-2-yl)-4,5-dihydro-1H-imidazole (4)
The mixture of thiophene-2-carbaldehyde (1) (3.55 mL, 38 mmol) and N-benzylethylenediamine (2) (6.00 mL, 40 mmol) in dry CH2Cl2 (125 mL) was stirred at 0 °C for 30 min, NBS (7.12 g, 40 mmol) was added to the mixture and the resulting solution was stirred overnight at rt. The reaction was diluted by CH2Cl2 (125 mL) and quenched by the addition of a mixture of Na2S2O5 aq (140 mL) and 10% NaOH aq (70 mL), the organic layer was washed by 10% NaOH aq (70 mL), dried over anhydrous Na2SO4 and evaporated in vacuo. The residue was purified by SiO2 column chromatography (CHCl3/MeOH, 100:0 → 99:1). TLC: Rf 0.35 (CHCl3/MeOH/NH3, 10:1:0.1,). Recrystallization gave the title compound 4 (7.18 g, 78%) as yellow needles; m.p. 52–53 °C (MeCN). 1H NMR (CDCl3) δ 3.50 (t, 2 H, J 10.2), 3.93 (t, 2 H, J 10.2), 4.57 (s, CH2, 2 H), 7.02–7.07 (m, 1 H), 7.27–7.32 (m, 3 H), 7.37 (t, 2 H, J 7.6), 7.41–7.45 (m, 2 H). 13C NMR δ 160.9 (Cq), 137.5 (Cq), 131.7 (Cq), 129.0 (CH), 128.9 (CH), 128.8 (CH), 127.7 (2C, CH), 127.5 (CH), 127.1 (2C, CH), 52.9 (CH2), 52.2 (CH2), 51.8 (CH2). IR (cm−1) ν = 3054 (w), 2930 (w), 2865 (m), 1709 (m), 1597 (m), 1522 (m), 1443 (m), 1358 (m), 1266 (m), 999 (m), 850 (w), 732 (w), 700 (m). EI-MS (m/z, M+): 243 (100%), 244 (16), 245 (5). HRMS (TOF ES+): m/z [M + H]+ calculated for C14H14N2S: 243.0951; found: 243.0950. Anal. calcd for C14H14N2S: C, 69.39; H, 5.82; N, 11.56%; found: C, 69.55; H, 5.78; N, 11.60%.