Imidazo-Fused Isoindoles by Pd(II)/Ag(I)-Promoted Intramolecular Dehydrogenative Coupling

Ligandless Palladium-Catalyzed Direct C-5 Arylation of Azoles Promoted by Benzoic Acid in Anisole

The palladium-catalyzed direct arylation of azoles with (hetero)aryl halides is nowadays one of the most versatile and efficient procedures for the selective synthesis of heterobiaryls. Although this procedure is, due to its characteristics, also of great interest in the industrial field, the wide use of a reaction medium such as DMF or DMA, two polar aprotic solvents coded as dangerous according to environmental, health, safety (EHS) parameters, strongly limits its actual use. In contrast, the use of aromatic solvents as the reaction medium for direct arylations, although some of them show good EHS values, is poorly reported, probably due to their low solvent power against reagents and their potential involvement in undesired side reactions. In this paper we report an unprecedented selective C-5 arylation procedure involving anisole as an EHS green reaction solvent. In addition, the beneficial role of benzoic acid as an additive was also highlighted, a role that had never been previously described.

Synthesis of N-Fused Triazole-Piperazine-Quinazolinones via One-Pot Tandem Click Reaction and Cross-Dehydrogenative Coupling

Herein, a one-pot protocol to synthesize tetracyclic triazole-piperazine-quinazolinone-fused N-heterocyclic scaffolds is reported. In this strategy, a tandem approach of two highly efficient synthetic reactions, click and cross-dehydrogentive coupling reactions, with high atom economy were employed to obtain the target N-fused scaffolds. Being highly functional group tolerable, this method has broad substrate scope. Interestingly, some of these derivatives showed strong white solid-state fluorescence.

Palladium-Catalyzed Dehydrogenative C-2 Alkenylation of 5-Arylimidazoles and Related Azoles with Styrenes

The construction of carbon–carbon bonds by direct involvement of two unactivated carbon–hydrogen bonds, without any directing group, ensures a high atom economy of the entire process. Here, we describe a simple protocol for the Pd(II)/Cu(II)-promoted intermolecular cross-dehydrogenative coupling (CDC) of 5-arylimidazoles, benzimidazoles, benzoxazole and 4,5-diphenylimidazole at their C-2 position with functionalized styrenes. This specific CDC, known as the Fujiwara–Moritani reaction or oxidative Heck coupling, also allowed the C-4 alkenylation of the imidazole nucleus when both 2 and 5 positions were occupied.