Sulfonated polystyrene cation exchange resin CAT600 was donated by Xian Electric Power Resin Factory, China. It showed a parameter as the density of SO
H groups in 4.9-5.1 mmol/g, specific surface area in 35.0-38.5 m
/g, average pore size in 50-100 Å. Unless otherwise stated, other chemicals (AR) were purchased from commercial sources and used without purification.
H NMR spectra were recorded using CDCl
as a solvent on a Bruker Avance 300 MHz spectrometer (75 MHz for
C NMR). GC analysis was performed on a Shimadzu GC-2010 apparatus equipped with an Rxi-1MS capillary column (30 m × 0.25 mm × 0.25 μm) connected to a hydrogen flame ionization detector. The GC condition was used as follows: a sampling/ detector temperature of 250 ℃, a column temperature of 190 ℃, nitrogen as carrier gas, nitrogen pressure 100 kPa, total flow rate: 50 mL/min, hydrogen flow rate: 40 mL/min, air flow rate: 400 mL/min. The temperature programme: 190 ℃ for 3 min, then rose to 250 ℃ with the rate 10 ℃/min, finally held at 250 ℃ for 1 min.
General Procedure for the O-Isopropylidenation.
To a suspension of the substrate (2 mmol) in dry acetone (10 mL), CAT600 (100 mg) was added. Then the mixture was stirred at 40 ℃ till the TLC (
-hexane-EtOAc 2:1) showed the completion of the reaction. The catalyst was separated by filtration, washed with acetone, dried, and reused for a consecutive run under the same reaction conditions. The filtrate was condensed to dry in vacuum, and the residue was dissolved in CH
(10 mL) and washed with 3 × 5 mL brine. The organic layer was dried over anhydrous Na
, filtered and evaporated to afford the crude product. Then the desired pure product was obtained by recrystallization from
-hexane. While, the silica gel column chromatography was used if the product existed in the liquid form.
The authors are thankful to financial support from the Natural Science Foundation of China (No. 21272144). References
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