ABSTRACT
Optical rotations were measured on a JASCO P-1010 polarimeter. 1H NMR-spectra (300 or 500 MHz) and 13C NMR-spectra (75 or 125 MHz) were recorded on Brüker spectrometers. Chemical shifts are given in ppm (δ) and were referenced to the internal solvent signal or to TMS used as an internal standard. Multiplicities are described as follows: s (singlet), br s (broad singlet), d (doublet), t (triplet), q (quadruplet), dd (doublet of doublet), ddd (doublet of doublet of doublet), dt (doublet of triplet), td (triplet of doublet), and m (multiplet). Coupling constants J are given in Hz. Infrared (IR) spectra were recorded on a Perkin-Elmer Fourier transform infrared (FTIR) system using diamond window Dura SamplIR II, and the data are reported in reciprocal centimeters (υ, cm-1). Mass spectra were recorded on Micromass LCT (ESI). Reactions were performed using oven-dried glassware under an atmosphere of dry argon. Silica gel 60 (35-70 µm) was used for ash chromatography. All reactions were monitored by thin-layer chromatography (TLC) (Merck 60 F254 aluminum sheets), the spots being
visualized with ultraviolet light and/or by charring with vanillin (1%) + sulfuric acid (5%) in EtOH. Reagents were from commercial sources and were used as received, unless stated otherwise. Triuoromethanesulfonic anhydride (Tf2O) was distilled under argon over P2O5 before use. Dichloromethane was distilled under argon over CaH2. Toluene and dimethylformamide were obtained from Acros Organics (Extra Dry over Molecular Sieve, Acroseal®) and were used as received. Solutions in organic solvents were dried with anhydrous MgSO4 and concentrated under reduced pressure.
