Am 400 instrument

All the chemicals and solvents were purchase from Sigma and used as such. Thin layer chromatography (TLC) was performed on precoated 0.5 mm thick silica gel 60 F₂₅₄ aluminum sheets. TLC plates were sprayed with 5% (v/v) aqueous solution of H₂SO₄, containing 4% (w/v) phosphomolybdic acid, 0.5% (w/v) ceric ammonium sulfate, and heated at 120 °C to visualize the spots. IR spectra were recorded on Shimadzu FTIR-8900 spectrometer (Shimadzu, Kyoto, Japan) as KBr pellets. ¹H NMR spectra were recorded on a Bruker AM-400 instrument (Bruker, Faellanden, Switzerland) in CDCl₃ solvent with tetramethylsilane as an internal standard. The chemical shifts are reported in ppm (δ) and coupling constant (J) are given in Hz. Mass spectra were obtained in an electron impact mode on Finnigan MAT-112 and MAT-113 spectrometers and ions are given in m/z (%).

¹H and ¹³C NMR spectra were acquired on a Bruker AM-400 instrument. Chemical shifts were given on the delta scale as parts per million (ppm) with tetramethylsilane (TMS) as the internal standard. IR spectra were recorded on a Nicolet Magna IR-550 spectrometer. MS spectra were recorded on a Mariner Mass Spectrum (ESI) equipment. Optical rotations of chiral compounds were measured on a PerkinElmer polarimeter at room temperature. Melting points were determined on a Mel-TEMP II melting point apparatus. Column chromatography was performed on silica gel. All chemicals are analytically pure. Compound 3 was prepared according to the previously reported procedures.^{21 (link)}