Metal-free protocol for the synthesis of novel 6-(het)aryl-5-aryl-5H-imidazo[4,5-b][1,2,5]oxadiazolo[3,4-e]pyrazines

New 5-aryl-5H-imidazo[4,5-b][1,2,5]oxadiazolo[3,4-e]pyrazines with the 6-positioned electron-rich (het)aryl substituents have been obtained from 5,6-diamino[1,2,5]oxadiazolo[3,4-b]pyrazines through the effective two-step strategy: the starting diamino compounds were treated with triethyl orthoformate, followed by the reaction with a π-excessive arene in thepresence of trifluoroacetic acid. The structures of target products were for the first time confirmed by X-ray diffraction analysis.