An Improved and Safer Synthesis of (R)- and (S)-4,4′-Diaminomethyl-BINAP

(R)‐ and (S)‐4,4′‐diaminomethyl‐BINAP were prepared in three steps from enantiomerically pure BINAPO in a global yield of 52 %. A regioselective bromination of BINAPO with NBS in HMimPF6 gave the desired 4,4′‐dibromo‐BINAPO in quantitative yield, and the recyclability of the ionic liquid was demonstrated. Copper cyanide cyanation of 4,4′‐dibromo‐BINAPO gave the 4,4′‐dicyano‐BINAPO in 70 % yield. Both enantiomers were characterized by NMR spectroscopy and HPLC analysis, and the structures were confirmed by X‐ray crystallography. The cyano and phosphane oxide groups of the resulting 4,4′‐dicyano‐BINAPO were reduced in one step to the corresponding 4,4′‐diaminomethyl‐BINAP by using tetramethyldisiloxane/Ti(OiPr)4 in 75 % yield. Previous synthesis of (R)‐ and (S)‐4,4′‐diaminomethyl‐BINAP was effective, but the method presented several drawbacks including long reaction times and the use of a large excess amount of a harmful reagent. We have developed an improved and safer synthetic route starting from optically active BINAPO.