300 or 400 mhz nmr spectrometer

All melting points were obtained on a Yanaco melting-point apparatus and were uncorrected. ESI mass spectra were performed on the Thermo Exactive Plus LC–MS spectrometer. Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker 300 or 400 MHz NMR spectrometer with TMS as an internal standard. Chemical shifts (δ values) and coupling constants (J values) were given in ppm and Hz, respectively. Column chromatography was performed with silica gel (160–200 mesh, Qingdao Haiyang Chemical, Qingdao, China). Unless otherwise noted, reagents and solvents were purchased from Acros Chemical Co, (Geel, Belgium) or other commercial providers and used without further purification.

Unless otherwise specified, all reactions were carried out under nitrogen atmosphere with magnetic stirring. All solvents and reagents were obtained from commercial sources and were purified according to standard procedures before use. ¹H and ¹³C NMR spectra were measured in CDCl₃ (¹H, 7.24 ppm; ¹³C 77.0 ppm) solution at 30 °C on a 300 or 400 MHz NMR spectrometer (Bruker, Rheinstetten, Germany), Mass spectra (Waters, Milford, MA, USA) were measured in a QTOF I (quadrupole–hexapole–TOF) mass spectrometer with an orthogonal Z-spray–electrospray interface. EM Science Silica Gel 60 was used for column chromatography while Thin Layer Chromatograpgy (TLC) (Merck, Darmstadt, Germany) was performed with precoated plates (Kieselgel 60, F₂₅₄, 0.25 mm).