To a solution of 3-bromo-1-naphthoic acid (0.40 g, 1.59 mmol) in CH2Cl2 (8 mL) at 0° C. are added methyl 3-amino-2,4-dimethylbenzoate (0.26 g, 1.43 mmol, see preparation 10) and triethylamine (0.78 ml, 5.38 mmol). After stirring the reaction mixture for 10 minutes, 1-propanephosphonic acid cyclic anhydride (50% solution in ethyl acetate, 2.03 ml, 3.18 mmol) is added via syringe and stirred at room temperature. After 16 hours, the reaction is diluted with water and extracted with ethyl acetate. The organic layers are combined and dried over magnesium sulfate, filtered, and concentrated under reduced pressure. The resulting residue is purified by flash chromatography (silica gel) with 5% EtOAc in hexane as eluent to afford the product as a white solid (0.52 g, 79%). Mass spectrum (m/z): 412.3 (M+1).
