A time-dependent, divergent synthesis of highly functionalized [1,2,3]triazolo[1,5- a ]pyrazin-4(5 H )-one (reaction time: 12 h) or 6,7-dihydro-[1,2,3]triazolo[1,5- a ]pyrazin-4(5 H )-one (reaction time: 2 h) scaffolds via a cascade azide-alkyne cycloaddition/hydroamination protocol is reported. The transformation features good functional group compatibility, broad substrate scope, high atom economy and avoidance of the use of transition-metal catalysts.