Magnesium-Promoted Benzidine-Type Rearrangement for Regioselective Construction of Polyfunctionalized Biaryls.

A magnesium-promoted benzidine-type rearrangement of 1,3-dihalonitroarenes with aryl Grignard reagents has been developed, enabling the highly regioselective and efficient synthesis of 1-amino-1'-hydroxy-4,4'-biaryls under simple, transition-metal-free conditions. A rational substrate design-featuring an ortho substituent (R) and two meta-substituted electron-withdrawing groups (X, Y)-steers the reaction trajectory, converting a previously minor [5,5]-sigmatropic migration into the dominant pathway. The transformation exhibits broad functional-group tolerance, excellent scalability, and provides direct and operationally straightforward access to polyfunctionalized biaryls. Furthermore, trifluoroacetamide-substituted nitroarenes undergo [5,5]-rearrangement followed by intramolecular cyclization to furnish CF3-substituted benzimidazoles with high regioselectivity. Overall, this study expands the conceptual scope of benzidine-type rearrangements and establishes a mechanistically tunable, sustainable strategy for constructing valuable biaryl and heteroaromatic scaffolds.