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 C-2-symmetric 2,2 '-bipyridine-alpha,alpha '-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-alpha,alpha '-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.