In the title compound, C13H11N5O, the exocyclic amino group of one purine molecule forms two intermolecular N—H...N hydrogen bonds to different ring N atoms of another molecule. The purine system is orientated almost perpendicular [77.96 (6)°] to the phenylethanone substituent. The preparation of the title compound occurred via a regioselective synthesis using the methyl(aqua)cobaloxime complex CH3Co(DH)2OH2 as a temporary auxiliary, and its X‐ray crystal structure confirmed the regioselective N‐alkylation of this molecule.