Bicyclo[2.2.1]heptane-1-methanesulfonic acid, 7,7-dimethyl-2-oxo-, (1S)- → 4-Chloro-6-methoxypteridin-7(8H)-one

To a 50 mL round bottom flask at room temperature with a Teflon stir bar was added 6-chloropyrimidine-4,5-diamine (25 g, 172.9 mmol, 1 equiv), and anhydrous acetonitrile (300 mL). Ethyl 2,2,2-triethoxyacetate (36.87 g, 224.8 mmol, 36.9 mL, 1.3 equiv) followed by a catalytic quantity of 10-camphorsulfonic acid (3 g, 12.97 mmol, 0.075 equiv) were then added. The stirred reaction mixture was then heated to reflux for 16 hours. The reaction mixture was then cooled to room temperature and concentrated under reduced pressure to approximately 100 mL on a rotary evaporator and poured into 500 mL of vigorously stirring ice water. The resulting slurry was rapidly stirred for 20 minutes, and the resulting tan solid was then filtered through a medium porosity glass fritted funnel and was dried on the vacuum line to give the title compound as a brown solid (25.7 g, 76% yield). 1H NMR (400 MHz, DMSO-d6): δ 13.32 (broad s, 1H), 8.62 (s, 1H), 3.99 (s, 3H). MS (EI) for C7H5ClN4O2: 213 (MH+).