Abstract

Palladium-catalyzed cross-coupling reactions have found extensive use in
the synthesis of biaryls and aryl-substituted heteroaromatics. Although powerful, the classical palladium-catalyzed cross-coupling reactions (Hiyama, Negishi, Kumada, Stille, Suzuki) can suffer from common limitations such as extensive reaction times, environmentally unfriendly by-products or reagents, and are atom inefficient. This has generated much attention in the past decades to further improve upon, or expand this type of reactivity, leading to new alternatives. Unfortunately, many newly developed alternatives require the extensive use of co-catalysts and/or additives, or lack selectivity.

Extending upon the decarboxylative cross-coupling protocol previously
developed by Forgione and Bilodeau, this work utilizes heteroaromatic sulfinates
as nucleophilic coupling partners. Heteroaromatic sulfinates have shown to be
readily synthesized by lithiation of the corresponding heteroaromatic followed by
quenching with sulfur dioxide gas, requiring little to no purification. Following
extensive optimization, an environmentally benign desulfinylative cross-coupling
protocol was developed requiring no co-catalyst or additives. The cross-coupling
of heteroaromatic sulfinates and aryl bromides occurs in predominantly aqueous
media utilizing an inexpensive catalyst system employing a palladium (II) source,
and requires short reaction times. The scope of this newly developed reactivity encompasses thiophene and furan sulfinates, which can be coupled with electron-deficient, electron-neutral and electron-rich aryl bromides in moderate to near quantitative yields.