To a stirred solution of 9H-xanthene-9-carboxylic acid (4.4 g, 19.4 mmol) in DCM (200 mL, 3 mol) was added dimethylpiperidin-4-yl-amine (2.5 g, 19.4 mmol). DIPEA (6.8 mL, 38.9 mmol) and HOBt (4.6 g, 34 mmol) were added to the mixture, followed by EDCI (4.5 g, 23.3 mmol). The mixture was stirred for 12 hours, then washed with water (300 mL), NaCl (sat.) (300 mL), dried over MgSO4 and then filtered. The solvent was removed under reduced pressure, and the crude material was purified via silica gel chromatography (10% MeOH/DCM w/1% NH3 (aq)) to yield the title compound (5.9 g).
