Copper-catalyzed, N-auxiliary group-controlled switchable transannulation/nitration initiated by nitro radicals: selective synthesis of pyridoquinazolones and 3-nitroindoles

Abstract

Within the scope of nitration reactions, the efficiency of sensitive heteroaromatics such as indoles is often eroded by various competitive oxidative decomposition pathways. Herein, we describe a strategy based on the judicious choice of N-auxiliaries, which stabilize the substrates as well as allow precise and predictable control over their reactivity with tert-butyl nitrite. Thus, the stage was set for the copper-assisted, controllable synthesis of pyridoquinazolones or 3-nitroindoles. Mechanistic studies implicate a switch in the mechanism, in which N-2-pyridylindoles reacted via a nitrosation/transannulation process and N-2-pyridoylindoles underwent an amide bond dissociation/nitration sequence. Notably, the subsequent removal of the auxiliary groups was not required in these reactions.