The 2-Pyridyl Problem: Challenging Nucleophiles in Cross-Coupling Arylations

Azine-containing biaryls are ubiquitous scaffolds in many areas of chemistry, and efficient methods for their synthesis are continually desired. Pyridine rings are prominent amongst these motifs. Transition-metal-catalysed cross-coupling reactions have been widely used for their synthesis and functionalisation as they often provide a swift and tuneable route to related biaryl scaffolds. However, 2-pyridine organometallics are capricious coupling partners and 2-pyridyl boron reagents in particular are notorious for their instability and poor reactivity in Suzuki-Miyaura cross-coupling reactions. The synthesis of pyridine-containing biaryls is therefore limited, and methods for the formation of unsymmetrical 2,2'-bis-pyridines are scarce. This Review focuses on the methods developed for the challenging coupling of 2-pyridine nucleophiles with (hetero)aryl electrophiles, and ranges from traditional cross-coupling processes to alternative nucleophilic reagents and novel main group approaches.

Transient directing ligand- and solvent-controlled C–H/C–H cross-coupling/quaternization cyclization/dequaternization of benzaldehydes with thiophenes

Rh(iii)-Catalyzed C–H/C–H cross-coupling between benzaldehydes and thiophenes has been developed to construct ortho-heteroaryl benzaldehydes, phenanthridinium- and phenanthridine-type polycycles.

Sustainable Fe-ppm Pd nanoparticle catalysis of Suzuki-Miyaura cross-couplings in water

Most of today's use of transition metal-catalyzed cross-coupling chemistry relies on expensive quantities of palladium (Pd). Here we report that nanoparticles formed from inexpensive FeCl3 that naturally contains parts-per-million (ppm) levels of Pd can catalyze Suzuki-Miyaura reactions, including cases that involve highly challenging reaction partners. Nanomicelles are employed to both solubilize and deliver the reaction partners to the Fe-ppm Pd catalyst, resulting in carbon-carbon bond formation. The newly formed catalyst can be isolated and stored at ambient temperatures. Aqueous reaction mixtures containing both the surfactant and the catalyst can be recycled.

Reactions of nitroxides 15. Cinnamates bearing a nitroxyl moiety synthesized using a Mizoroki-Heck cross-coupling reaction

Cinnamic acid derivatives bearing a nitroxyl moiety (2,2,6,6-tetramethyl-1-oxyl-4-piperidyl 3-E-aryl acrylates) were synthesized in 30–100% yield using a Mizoroki–Heck cross-coupling reaction between 4-acryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl and iodobenzene derivatives in the presence of palladium(II) acetate coordinated with a tri(o-tolyl)phosphine ligand immobilized in a polyurea matrix.

Palladium-catalyzed ligand-free and efficient Suzuki–Miyaura reaction of heteroaryl halides with MIDA boronates in water

A simple and environment-friendly protocol for the palladium-catalyzed Suzuki–Miyaura reaction of heteroaryl halides with N-methyliminodiacetic acid (MIDA) boronates in pure water is developed.