Transition-Metal-Free Direct Arylation: Synthesis of Halogenated 2‑Amino-2′-hydroxy-1,1′-biaryls and Mechanism by DFT Calculations

A transition-metal-free, regioselective direct aryl–aryl bond-forming process for the synthesis of halogenated 2-amino-2′-hydroxy-1,1′-biaryls that are currently either inaccessible or challenging to prepare using conventional methods is disclosed. The addition of ArMgX to an <i>o</i>-halonitrobenzene at low temperature generates a transient <i>N</i>,<i>O</i>-biarylhydroxylamine that rapidly undergoes either [3,3]- or [5,5]-sigmatropic rearrangement in one-pot to form a 2-amino-2′-hydroxy-1,1′-biaryl or 1-amino-1′-hydroxy-4,4′-biaryl, respectively. The periselectivity is controlled by the choice of solvent and temperature. This direct arylation process is also readily scalable (1–10 mmol). DFT calculations suggest that from the <i>N</i>,<i>O</i>-biarylhydroxylamine intermediate there is a low-energy stepwise pathway that involves initial Mg-mediated N–O bond cleavage followed by pathway branching toward either [3,3]- or [5,5]-rearrangement products via C–C bond formation and rearomatization