H and 13
C spectra were recorded on an Inova 600 (Varian, Palo Alto, CA, USA) spectrometer operating at 600 MHz (for 1
H-NMR) and 150 MHz (for 13
C-NMR). Chemical shifts refer to the solvent for 1
H and 13
C-NMR (δ = 1.96 and δ = 118.26, respectively, for CD3
CN; δ = 2.50 for 1
H-NMR in DMSO-d6
). Signal multiplicities were established by Distortionless Enhanced by Polarization Transfer (DEPT90) experiments. Chemical shifts were measured in δ. J
values are given in Hertz. Electron spray ionization mass spectra (ESI-MS) were recorded with a WATERS ZQ 4000 instrument (Waters Corporation, Milford, MA, USA). The IR spectrum was recorded with a Fourier transform spectrophotometer PerkinElmer FT-IR Spectrum Two (PerkinElmer, Waltham, MA, USA) in the 4000−800 cm−1
wavelength range using a NaCl cell. The UV/Vis spectrum was recorded using a PerkinElmer UV-Vis Lambda 12 spectrophotometer (PerkinElmer, Waltham, MA, USA). Chromatographic purifications (FC) were carried out on glass columns packed with silica gel (Merck grade 9385, 230−400 mesh particle size, 60 Å pore size) at medium pressure. Thin-layer chromatography (TLC) was performed on silica gel 60 F254
-coated aluminum foils (Fluka, Darmstadt, Germany). 7-Chloro-4,6-dinitrobenzofuroxan was synthesized according to the literature [19
], and 2-aminothiazole was purchased by Sigma-Aldrich (Darmstadt, Germany).
4,6-Dinitro-7-(thiazol-2-ylamino)benzo[c][1,2,5]oxadiazole 1-oxide (3)
In a round-bottom flask, 7-chloro-4,6-dinitrobenzofuroxan (1) (156 mg, 0.6 mmol) and 2-aminothiazole (2) (120 mg, 1.2 mmol) were added and dissolved in acetonitrile (10 mL). Immediately after mixing, the solution became dark brown. The mixture was stirred at room temperature overnight. The reaction course was monitored by TLC (eluent: ethyl acetate/acetone 9/1). The product was purified by a chromatography column on silica gel (eluent ethyl acetate/acetone 9/1). The pure product yield was 89 mg, 45%.
Red plates, m.p. >300 °C (CH3Cl); 1H-NMR (600 MHz, CD3CN, 25 °C) δ = 8.84 (s, 1H), 7.35 (d, J = 3.7 Hz, 1H), 7.11 (d, J = 3.7 Hz, 1H); NH not detected, likely due to the exchange with HDO present in the deuterated solvent; 13C-NMR (150 MHz, CD3CN) δ = 172.7 (C), 149.0 (C), 142.5 (C), 140.1 (CH), 135.4 (CH), 127.1 (C), 116.5 (CH), 116.2 (C), 113.4 (C); ESI-MS– (m/z): 323 [M − H]−; FT-IR: ν (cm−1) 3164, 3004, 2944, 2293, 2261, 2245, 1438, 1374, 1039, 918; UV-Vis: λmax = 495 nm, ε495 = 12,933 L mol−1 cm−1; elemental analysis for C9H4N6O6S, calculated C, 33.34; H, 1.24; N, 25.92, found C, 33.40; H, 1.26; N, 25.89.