Synthesis of bicyclic vinyl triazenes by Ficini-type reactions

Cyclic olefins with triazene functions can display interesting reactivity, but synthetic access to these compounds is limited thus far. Herein, we describe the synthesis of cyclobutenyl triazenes fused to cyclopentanone or cyclohexanone rings. The bicyclic compounds are obtained by Lewis acid-catalyzed [2 + 2] cycloaddition reactions of 1-alkynyl triazenes and enones. In the presence of Me2AlCl, bicyclic [4.2.0] triazenes rearrange into [3.2.1] ring systems. The triazene function in the latter can be used for further functionalizations. Notably, we show that vinyl triazenes can serve as substrates for Pd-catalyzed cross-coupling reactions with arylboronic acids.