A solution of 6-bromo-5-(2,4-difluorophenoxy)-1H-1,2,3-benzotriazole (0.047 g, 0.14 mmol) and p-toluenesulfonic acid monohydrate (0.0027 g, 0.014 mmol) in chloroform (0.65 mL) was treated with dihydropyran (0.0197 mL, 0.216 mmol) and stirred at 60° C. for 1 h. The reaction mixture was diluted with dichloromethane and washed with saturated sodium bicarbonate. The aqueous layer was separated and re-extracted with dichloromethane. The combined organic layers were separated, washed with water and brine, dried with magnesium sulfate, filtered, and concentrated to a crude oil. Purification by flash column chromatography (100% hexanes to 60% EtOAc/hexanes) gave the desired product as a mixture of isomers that was used without further purification.
