Preparation of 3-diazoindolin-2-imines via cascade reaction between indoles and sulfonylazides and their extensions to 2,3-diaminoindoles and imidazo[4,5-b]indoles.

3-Diazoindolin-2-imines were constructed from indoles and sulfonylazides via an electronically matched 1,3-dipolar cycloaddition and a subsequent dehydroaromatization/ring-opening cascade. The reaction between 3-substituted indoles and sulfonyl azides provided 2-aminoindoles, while 2-substituted indoles furnished 3-aminoindoles. Moreover, 2,3-diaminoindoles could be prepared from the resulting 3-diazoindolin-2-imines and secondary amines via a rhodium-catalyzed amination. Further extension of 2,3-diaminoindoles led to the formation of imidazo[4,5-b]indoles.