Efficient Synthesis of a C₂-Symmetric 2,2'-Bipyridine-α,α'-1-t-butyl-diol Ligand by Stereoselective Double Hydrogen Transfer to a 2,2'-Bipyridine-diketone

An efficient and practical method was developed for the synthesis of C₂-symmetric 2,2'-bipyridine-α,α'-1-t-butyl-diol ligands. The disclosed synthesis involves the Ullmann homocoupling of a keto bromo-pyridine under NiCl₂/Zn/PPh₃ conditions, followed by the stereoselective double hydrogen transfer to the obtained 2,2'-bipyridine-diketone using Ru^II Noyori-Ikariya catalysts. This approach allowed the successful synthesis of 2,2'-bipyridine-α,α'-1-t-butyl-diol, i.e (S,S)-Bolm's ligand, with a quantitative yield and an excellent stereoselectivity (ee>99.5 %, de>99.5 %), with an overall yield of 69 % from easily accessible starting materials.