400 nmr or 500 nmr spectrometer

¹H and ¹³C NMR spectra were recorded on a Varian 400 NMR or 500 NMR spectrometer using CDCl₃ or DMSO-d₆ as a solvent and tetramethylsilane (TMS) as an internal standard. Chemical shift (δ) are reported in parts per million (ppm) and coupling constants (J) are reported in Hertz (Hz). Splitting patterns are indicated as follows: s, singlet; d, doublet; dd, double doublet; t, triplet; m, multiplet; brs, broadsinglet. Melting points were measured with a micro melting point apparatus (MP-J3, Yanaco) and were uncorrected. High-resolution mass spectra were determined on Thermo Exactive Orbitrap plus mass spectrometer. Reactions were monitored by TLC (silica gel GF254). Products were purified by flash chromatography on silica gel (200–300 mesh) by using the solvent system(s) indicated. All the starting materials were obtained from commercially available sources and used without further purification, unless otherwise specified. The purity of all final compounds was ≥95% and established by HPLC, which was carried out on a Thermo Fisher Accela HPLC system (Thermo Fisher Scientific, Bremen, Germany) with an Agilent Zorbax SB-C18 column (5 μm, 2.1 × 50 mm), 40 °C, 254 nm, flow rate: 0.3 mL/min, and a gradient of 5–95% MeCN in water (containing 0.1 % of HCOOH) in 10 min.