Synthesis of 6-phenyl-2,2′-bipyridine ligands bearing polyaromatic substituents

A simple protocol for the efficient preparation of substituted 6-phenyl-2,2′-bipyridine derivatives is described. An inverse Diels–Alder reaction between a 3-phenyl-5-pyridyl-1,2,4-triazine and an electron-rich ethynyl species at high temperature provides a mixture of two products easily separable by column chromatography. The most encumbered isomer is favoured, likely due to favourable π–π stacking interactions in the transition state. A variety of those ligands suitable for the synthesis of cyclo-metallated complexes have been produced.