Ruthenium-catalyzed synthesis of tricyclic 1,5-fused 1,2,3-triazole piperazines

A double cyclization strategy, involving sequential ruthenium-catalyzed azide alkyne cycloaddition (RuAAC) and hydrogen borrowing, allows the rapid assembly of tricyclic 1,5-fused 1,2,3-triazole piperazines from a proline scaffold. The initial RuAAC-cyclization proceeded in up to 99% yield under mild reaction conditions, while cyclative hydrogen borrowing afforded the desired fused triazole piperazines in up to 75% yield. Both reaction steps are highly atom economic and we envisage that the tricyclic products can find applications in asymmetric transformations, as well as in the synthesis of products of biological interest.