A metal-free, iodine-catalyzed protocol has been established for constructing rarely reported mesoionic 1,2,4triazolo5,1-aisoquinoliniums, using CHP as an oxidant. This synthesis is achieved via a formal 3+2 annulation between 3,4-dihydroisoquinolin-2(1H)-amines and isocyanates. The operationally simple, one-pot process proceeds under mild conditions through a cascade sequence of hydroamination, intramolecular cross-dehydrogenative coupling (CDC), and oxidative dehydrogenation. It features broad substrate tolerance and high atom and step economy. Furthermore, preliminary mechanistic studies indicate that the transformation likely proceeds via a hypoiodite-mediated pathway.
Sun et al. (Tue,) studied this question.