The reaction of tetracyanoethylene (I) with HBr, followed by a treatment with NaOH, gives 2-amino-5-bromo-1H-pyrrole-3,4-dicarbonitrile (II), which is treated with triethyl orthoformate (III) in refluxing acetonitrile to yield the ethoxymethyleneamino derivative (IV). The alkylation of (IV) with 2-phenylethyl chloride (V) by means of NaH affords the 2-bromo-5-(ethoxymethyleneamino)-1-(2-phenylethyl)pyrrole-3,4-dicarbonitrile (VI), which is cyclized with ammonia in methanol to provide the pyrrolo[2,3-d]pyrimidine derivative (VII). Finally, this compound is treated with liquid ammonia to obtain the target diaminopyrrolo[2,3-d]pyrimidine derivative.