A transition-metal-free azide-alkyne cycloaddition/hydroamination cascade reaction for the construction of triazole-fused piperazin-2-ones

A time-dependent, divergent synthesis of highly functionalized [1,2,3]triazolo[1,5-a]pyrazin-4(5H)-one (reaction time: 12 h) or 6,7-dihydro-[1,2,3]triazolo[1,5-a]pyrazin-4(5H)-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. A time-dependent, divergent synthesis of [1,2,3]triazolo[1,5-a]pyrazin-4(5H)-one (reaction time: 12 h) or 6,7-dihydro-[1,2,3]triazolo[1,5-a]pyrazin-4(5H)-one (reaction time: 2 h) scaffolds is reported.