Synthesis of Substituted 2,2'-Dinitrobiphenyls by a Novel Solvent-Free High Yielding Ullmann Coupling Biarylation.

Solvent-free reaction using a high-speed ball milling technique has been applied to the classical Ullmann coupling reaction for the first time. Biarylation of 2-iodonitrobenzene was achieved in quantitative yield when performed in a custom-made copper vial through continuous shaking without additional copper or solvent. The product was solid, NMR ready and required no lengthy extraction for purification. This reaction was cleaner, and faster than solution phase coupling which requires longer reaction time in high boiling solvents, added copper catalyst, and lengthy extraction and purification steps. Gram quantities of the biaryl compound were synthesized in larger copper vials. This is a general method that can be used to effectively reduce industrial waste en route to sustainability.