To a round-bottomed flask (125 mL) equipped with a reflux condenser was added theappropriate amine (0.05 mmol), toluene (40 mL) and formaldehyde (37%, 4.1 mL).The solution was brought to reflux using an external oil bath and kept stirring for 30min. Then, the toluene was evaporated under reduced pressure, and the residue wasdissolved in ethyl acetate and washed with a saturated aqueous solution of sodiumchloride. After evaporation of the solvent under reduced pressure in a rotaryevaporator, the residue was purified by silica gel column chromatography usinghexane/ethyl acetate 9:1 as the eluent.
