Alkylamination of pteridines by primary alkylamines ‐ potassium permanganate

Reaction of 7‐phenyl, 7‐p‐methoxyphenyl, 7‐ t ‐butyl‐ and 6,7‐diphenylpteridine with ethylamine and t ‐butylamine in the presence of potassium permanganate leads to the introduction of the ethylamino or t ‐butylamino group at C‐4 in the above‐mentioned pteridines. In the reaction of ethylamine/potassium permanganate besides the 4‐(ethylamino)pteridine derivatives 2‐amino‐3‐formytpyrazines are obtained as side‐products. In the reaction with t ‐butylamine/potassium permanganate the corresponding pteridin‐4‐ones are obtained as by‐products. The 1 H nmr spectroscopic studies have revealed that at room temperature ethylamine easily gives a σ‐adduct at C‐4, yielding a 4‐(ethylamino)‐3,4‐dihydropteridine derivative. t ‐Butylamine, however, only gives with the pteridines addition at C‐4 at low temperature, i.e . at −40°. This adduct dissociates at room temperature. n ‐Propylamine and n ‐butylamine show the same behavior as ethylamine.