Visible-light-promoted [3+2] Cycloaddition Of Hydrazone With Hypervalent Iodine Diazo Compounds

As a kind of organic synthesis reagents with special structure and high activity,diazo compounds have outstanding contributions in the fields of organic chemistry,medicinal chemistry and materials chemistry.Generally,diazo compounds as carbon nucleophiles,nitrogen electrophiles,1,3-dipoles,and carbon-based precursors participate in a board array of significant processes.In contrast,diazo compounds as diazomethyl radicals have been scarcely explored,which is mainly due to the lack of efficient sources of diazomethyl radicals.Recently,hypervalent iodine diazo reagents could act as the precursors of diazomethyl radicals,providing a novel strategy for diazomethyl radicals in organic synthesis.Therefore,it is of great importance to explore this building block for access to diverse transformations and enrich the variety of diazo chemistry.In this study,we developed visible-light-induced[3+2]cyclization reactions of hydrazones with hypervalent iodine diazo reagents as diazomethyl radical precursors.This reaction provides a new method to construct the C-C and N-N bonds conveniently and efficiently for the synthesis of a series of functional 1-amino-1,2,3-triazoles.Under optimal conditions,the target product can be obtained with a good yield in a gram-scale experiment or in a one-pot experiment.To the late-stage functionalized aldehyde hydrazones of natural products,the reaction can also proceed smoothly.In addition,further experimental derivatization studies were carried out.To gain insight into the reaction mechanism,the following investigations were studied:1)Free radical capture experiments demonstrated that the reaction could undergo a free radical process;2)a series of fluorescence quenching experiments indicated that hypervalent iodine diazo reagents efficiently quenched the*[Ru(bpy)₃]²⁺excited state;3)The capture of?-diazohydrazone demonstrated that the cyclization process requires the assistance of a photocatalytic cycle.Based on the above results,we proposed a possible reaction mechanism.