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