Autopol 3 automatic polarimeter

Reagents and solvents were purchased from commercial suppliers and used as received unless otherwise noted. Dry solvent was obtained following the standard procedure. All reactions were performed under N₂ atmosphere unless otherwise indicated. Analytical silica gel 60 F₂₅₄-coated TLC plates were purchased from EMD Chemicals, Inc. and were visualized with UV light or by treatment with phosphomolybdic acid (PMA), Dragendorff’s reagent, or ninhydrin. Whatman Purasil 60A silica gel 230−400 mesh was used for flash column chromatographic purifications. Proton nuclear magnetic resonance (¹H NMR) spectra were measured on Varian 400 and 600 MHz NMR spectrometer, using tetramethylsilane (TMS) as an internal standard. The NMR solvent used was either CDCl₃ or CD₃OD unless otherwise indicated. Optical rotations were recorded on Autopol III automatic polarimeter (Rudolph Research Analytical). Melting points were recorded using a MEL-TEMP II (Laboratory Devices Inc., U.S.) capillary melting point apparatus. Purity of the compounds was determined by elemental analysis and was within ±0.4% of the theoretical value (≥95% purity). Elemental analyses were performed by Atlantic Microlab, Inc., GA, USA. Selected compounds were furher analyzed by reverse phase HPLC (Waters 2489 Alliance Integrated System, USA) to check for purity.

Optical rotations were measured on a RUDOLPH Research Analytical Autopol III Automatic Polarimeter. IR spectra were recorded on a Nicolet Nexus 470 FTIR spectrophotometer. HRMS were obtained on an Orbitrap mass spectrometer with electrospray ionization (ESI). NMR spectra were obtained on a Bruker Fourier 300 spectrometer in CDCl₃. The chemical shifts are given in ppm referenced to the respective solvent peak, and coupling constants are reported in Hz. Anhydrous THF and dichloromethane were purified by a PureSolv MD 7 Solvent Purification System from Innovative Technologies (MB-SPS-800). All other reagents and solvents were purchased from commercial sources and were used without further purification. Silica gel column chromatography was performed using silica gel (32–63 μm). Preparative thin-layer chromatography (PTLC) separations were carried out on thin layer chromatography plates loaded with silica gel 60 GF254 (EMD Millipore Corporation). Starting materials 9 and 10 were synthesized using the procedure previously described by us.^{21 (link)}