Hydroxylamine umpolung in copper-catalyzed cross-coupling reactions to synthesize N-Arylhydroxylamine derivatives

Abstract

Hydroxylamine derivatives are well-established nitrogen precursors that undergo various transition metal-catalyzed transformations via the cleavage of the nitrogen–oxygen bond. Conversely, the development of a reagent containing a transferable electrophilic hydroxylamine has been elusive due to the inherent fragility of the N–O bond. Herein, we demonstrate the utility of hypervalent iodine chemistry to synthesize a reagent for the transfer of an electrophilic N–O moiety. Reagent 2 is a hydroxylamine umpolung that allows the formation of highly valuable N-arylhydroxylamine synthons via a copper-catalyzed cross-coupling reaction with boronic acids. The process with reagent 2 showed a wide functional group tolerance, especially with other electrophilic functional groups, and exhibited an orthogonal reactivity compared to other methods for synthesizing N-arylhydroxylamine derivatives. These can be subjected to Cope rearrangement and postfunctionalization, affording a variety of nitrogen-containing building blocks. Experimental and in silico mechanistic studies propose a catalytic cycle that involves the formation of a copper(II)-hydroxylamine species as the initial step. This species then reacts with boronic acid to produce the desired product.