EXPERIMENTAL SECTION General. Products were isolated by flash chromatography using 60 Å silica gel and a Biotage Isolera chromatography unit. 1 H and 13 C NMR was carried out using a 300 or 500 MHz spectrometer. Chemical shifts were referenced to NMR solvent signals.IR spectrum was collected on a Shimadzu IRAffinity-1S spectrometer. The syringe pump used was a KD Scientific Legato dual syringe pump. Reagents and solvents were purchased from commercial suppliers and used as received. Fuming sulfuric acid is highly corrosive -it should be handled in an efficient fume hood by appropriately trained individuals utilizing personal protective gear.