The reaction completion was judged by thin layer chromatography (TLC) monitoring. At the end, the reaction mixture was diluted with dichloromethane (20 mL) and washed with an aqueous saturated NaHCO3 solution. The aqueous layer was separated and washed twice with dichloromethane (10 mL). The combined organic extract was dried over anhyd Na2SO4 and evaporated under reduced pressure. The crude product was purified by a short-pad silica gel column chromatography.