Synthesis of 2,5-diaminopyrazine derivatives via dimerization of 2H-azirin-3-amines

Abstract

The 2-monosubstituted 2H-azirin-3-amine (5c) was prepared conveniently by subsequent treatment of N-methyl-N-phenylpropanamide in THF with LDA, diphenyl phosphorochloridate (DPPCl), and sodium azide in DMF. In the absence of nucleophiles, the reaction of 5c in THF with BF3·OEt2 at -78°C yields 2,5-dihydro-2,5-dimethyl-3,6-bis(N-methyl-N-phenylamino)pyrazinium tetrafluoroborate (11). Treatment of the latter with NaOH yields the corresponding 2,5-dihydropyrazine derivative (12), whereas dehydrogenation with DDQ leads to 2,5-dimethyl-3,6-bis(N-methyl-N-phenylamino)pyrazine (13). The structures of 12 and 13 were established by X-ray crystallography