TFA-catalyzed cascade annulation of thioamides with aromatic hydrazides/amines: An internal oxidant-triggered protocol to diverse N-heterocycles

An internal oxidant-triggered highly efficient protocol for the synthesis of diverse N -heterocycles (benzothiazoles, benzoxazoles, quinazolines, and 1,3,4-oxadiazoles) by TFA-catalyzed cascade annulation of thioamides with aromatic hydrazides or ortho -functionalized arylamines is described. In this transformation, thioamides act as a “C1” source as well as an internal oxidant, constructing a C=N double bond and a C-X (O/S/N) bond. The protocol is characterized by simple operation, metal-free conditions, broad substrate scope, good yields, and gram-scale synthesis. In addition, products can be further modified by Buchwald-Hartwig amination reactions, to a series of novel fluorescent compounds, which exhibit significant fluorescence performance with large Stokes shifts. An internal oxidant-triggered highly efficient protocol for the synthesis of diverse N -heterocycles (benzothiazoles, benzoxazoles, quinazolines, and 1,3,4-oxadiazoles) via TFA-catalyzed cascade annulation of thioamides with aromatic hydrazides or ortho -functionalized arylamines is described.