α-Acidic isocyanides are versatile reagents in organic synthesis, especially for the synthesis of five-membered heterocycles via [3 + 2]-cycloaddition reactions with activated multiple bonds. In this communication, the first [3 + 3]-cross-cycloaddition of α-acidic isocyanides with 1,3-dipolar azomethine imines to generate a series of 1,2,4-triazine derivatives with significant regiochemical control under mild catalytic reaction conditions is described. This new strategy shows that α-acidic isocyanides can also be taken as potent reagents for the synthesis of six-membered heterocycles through [3 + 3]-cross-cycloaddition reactions with 1,3-dipoles.