A modular synthesis of highly substituted 3-azapyrroles has been developed using a three-step sequence comprising copper-catalyzed alkyne–azide cycloaddition (CuAAC), N–H bond insertion, and cyclodehydration. 1-Sulfonyl-1,2,3-triazoles (1-STs) can be accessed from common alkyne and sulfonyl azide building blocks by CuAAC using CuTC. Rhodium(II)-acetate-promoted 1-ST denitrogenation results in highly electrophilic rhodium azavinyl carbenes that, here, underwent insertion into the N–H bond of secondary α-aminoketones to form 1,2-aminoalkenes. These products were cyclized and dehydrated using BF3·OEt2 into highly substituted 3-azapyrroles. The three steps (CuAAC, N–H bond insertion, and cyclodehydration) could be telescoped into a one-pot process. The method proved to be highly efficient and tolerated a wide range of substituents.

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Hongwei Qiao

Papers

Synthesis of xanthones from 4-(2-phenoxyphenyl)-1-tosyl-1H-1,2,3-triazole via rhodium-catalyzed annulation/oxidation