Cycloaddition and Skeleton Rearrangement of Heterocyclic Ketene Aminals (HKAs) with 1‑Diazonaphthalen-2(1H)‑ones for the Synthesis of Functionalized 1,2,3-Triazoles

We developed a protocol for the synthesis of highly functionalized 5,6-dihydro-imidazo[1,2-c][1,2,3]triazole derivatives 4–5 (DHITs) from 1-diazonaphthalen-2(1H)-one derivatives with heterocyclic ketene aminals (HKAs). This strategy involved cycloaddition and skeletal rearrangement entailing the heating of a mixture of substrates 1 with HKAs 2–3 and THF without any catalyst. As a result, a series of DHITs 4–5 were produced by cleaving one bond (1 CN bond) and forming three bonds (1 N–N and 2 C–N bonds) in a single step. This protocol achieved the dual functionalization of diazo building blocks involving both the aromatic nitrogen alkylation reaction to form an ArC–N bond without any metal catalyst and the intermolecular cycloaddition of the NN bond. These strategies can be used to synthesize functionalized DHITs for combinatorial and parallel syntheses via one-pot reactions without any catalyst.