Synthesis of Pyrazines from Diaza-butadienes and 1,2-Diamines

Significance

The 1,4-addition of 1,2-diamines to 1,2-diaza-1,3-butadienes bearing carboxylates, carboxamides, and phosphorylated groups and subsequent internal heterocyclization leads to piperazinones, quinoxalines, tetrahydro-2-pyrazinones, tetrahydropyrazines, and dihydropyrazine derivatives using solution, solvent-free or solid-phase conditions. Subsequent oxidation of the latter two systems affords pyrazines. The scope of the reaction is emphasized by the 50 cited examples. Under solvent-free conditions, the reactions were carried out at the melting point of the amine to guarantee a homogeneous reaction mixture. Depending on the substituent R³, pyrazine-2-phosphorylates were formed in good yields and tetrahydro-2-pyrazinones in moderate yields.