Phenol → Phenyl cyanate

To a oven dried 500 mL 3-neck round bottom flask equipped with a overhead stirring, a septa, a thermocouple and the nitrogen inlet, phenol (20.0 g, 0.210 mol), diethyl ether (Et2O, 290 mL) and cyanic bromide (BrCN, 23.0 g, 0.210 mol, 1.0 equiv) were added at room temperature. The resulting solution was cooled down to 0-3° C. before triethylamine (TEA, 61.9 mL, 0.442 mol, 2.1 equiv) was added dropwise via syringe over 25 min. The addition of triethylamine to reaction mixture was mildly exothermic and the reaction temperature went up to as high as 15° C. After addition of triethylamine, the reaction mixture became a white slurry which was stirred vigorously at 0° C. for 2 h at 5-15° C. When the reaction was deemed complete as confirmed by TLC and LCMS, the reaction mixture was diluted with pentane (150 mL, 1.30 mol). The precipitated triethylamine hydrochloride was filtered off and the salt was washed with diethyl ether and pentane (1 to 1 by volume, 200 mL). The filtrate was then concentrated under reduced pressure to remove the majority of the solvent, and the residue, which contains the crude cyanatobenzene (6), was directly used in the subsequent reaction without further purification assuming the theoretical yield.