Application of carbenoid N–H insertion in the synthesis of the tricyclic 1,4-dihydropyrazines

The N–H insertion of the substituted anilines with 2-diazo-1,3-cyclohexanedione or 2-diazo-1,3-cyclopentanedione and subsequent cyclization enabled an efficient synthesis of a novel series of tricyclic 1,4-dihydropyrazines.