To a solution of 2-amino-5-mesityl-3,7-dimethyl-3,7-dihydro-4H-pyrrolo[2,3-d]pyrimidin-4-one (100 mg, 0.34 mmol) and N,N-dimethylformamide (2 ml) was added sodium hydride (60% in oil, 27 mg, 0.66 mmol) at 0° C. and stirred for 0.5 hour. After stirring at room temperature for 0.5 hour, to the mixture was added a solution of n-BuI (184 mg, 1.00 mmol) and N,N-dimethylformamide (1 ml) at 0° C. and stirred for 0.5 hour. After stirring at room temperature for 1 hour, the mixture was diluted with water (20 ml) and extracted with ethyl acetate (50 ml×2). The extracts were combined, washed with brine, dried over sodium sulfate and concentrated in vacuo. The residue was purified by silica gel chromatography eluting with hexane/ethyl acetate (4:1) to give 85 mg (62%) of the title compound as an oil.
