Phosphorus oxychloride → ethyl 4-(4-chloro-5H-pyrrolo[3,2-d]pyrimidin-6-yl)benzoate hydrochloride

A mixture of ethyl 4-(4-oxo-4,5-dihydro-3H-pyrrolo[3,2-d]pyrimidin-6-yl)benzoate (2.97 g) and phosphoryl chloride (16.45 g) was stirred at 110° C. for 1 hr, dioxane (10 mL) was added and the mixture was heated under reflux for 4 hrs. After concentration under reduced pressure, ethanol (30 mL) was added to the residue and, after stirring at room temperature for 30 min, the precipitated solid was collected by filtration. The solid was washed with ethanol and dried under reduced pressure at 60° C. to give the title compound (3.34 g).