Pd(0)-Catalyzed Decarboxylative Coupling and Tandem C–H Arylation/Decarboxylation for the Synthesis of Heteroaromatic Biaryls

Abstract

An effective Pd(0) carbene complex was successfully employed in the decarboxylative coupling of the heteroaromatic carboxylic acids (imidazo[1,2-a]pyridine and isoxazole) with aryl halides. For carboxyindoles, either decarboxylative coupling or tandem C-H arylation and decarboxylation occurred, leading to the formation of C2-monoarylated indoles.

Palladium(0) complexes of N-heterocyclic carbene ligands with dangling NMeC O functionalities: Synthesis, reactivity and application in Mizoroki–Heck reactions

“…The new Pd(0) complexes 3a-d were then prepared following our reported procedure for similar compounds, employing compound A as the Pd(0) precursor [5], which afforded yellow solids with decent yields (58-89%) (Scheme 1). Complexes 3e [6] and 4b [5] were reported by us previously. For a comparative purpose, we also synthesized complex 4e, featuring dangling NH(C@O) and N-mesityl groups on the carbene moieties.…”

“…Starting chemicals were purchased from commercial sources and used as received. Compounds 1e [6], A [12], 3e [6] and 4b [5] were prepared according to the literature procedures. 1 H, 13 …”

“…The expected product resulting from oxidative addition (3e1) was, however, not observed. The diiodopalladium(II) complex with two trans coordinated NHC ligands (6) together with decafluorobiphenyl (DFBP, 5) were isolated as the major products. The structure of 6 was confirmed by single-crystal X-ray diffraction analysis (vide infra).…”

Decarboxylative Coupling Techniques

“…In 2012, Lee and coworkers [21] reported a new monometallic Pd catalyst for the regioselective synthesis of decarboxylated biaryls from heteroaromatic carboxylic acids (Scheme 3.9). Using aryl bromides as coupling partners, the desirable biaryls were obtained in high yields (73-88%).…”

“…Decarboxylative arylation of an imidazo[1,2-a]pyridine-3-carboxylic acid and an 3-(4-fluorophenyl)-5-methylisoxazole-4-carboxylic acid with aryl halides, as described by Lee and coworkers[21].…”