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.

ABSTRACT

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 RuII 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.