A catalyst-free aqueous mediated multicomponent reaction of isocyanide: Expeditious synthesis of polyfunctionalized cyclo[b]fused mono-, di- and tricarbazoles

A catalyst-free, facile, and atom/step economical isocyanide-based multicomponent reaction is developed for the rapid and efficient construction of polyfunctionalized cyclo[b]fused carbazoles. This transformation proceeds smoothly in aqueous media, starting from the easily available 2-alkenyl aryl isocyanides, aldehydes, and cyclic diketones. Moreover, both structurally complex dicarbazoles and tricarbazoles were conveniently generated in good yields by this cascade protocol, where up to six rings and twelve C–C bonds were successively created. In addition, the mechanism is proposed on the basis of control experiments, which reveals a sequential Knoevenagel condensation/[4 + 1] cycloaddition/intramolecular Diels–Alder reaction/C–O scission/elimination process.