Partially hydrogenated 1,1′-binaphthyl as ligand scaffold in metal-catalyzed asymmetric synthesis

Although chiral binaphthyl-type ligands are already known to be effective over a broad spectrum of reactions, they sometimes fail in providing high enantioselectivities in some catalytic asymmetric reactions. This article summarizes recent attempts to elevate their performance by partly hydrogenating the naphthyl components of the binaphthyl. The synthetic routes to some of these ligands are briefly outlined. Positive results are observed in asymmetric hydrogenation, alkylation, borane reduction, epoxidation and hetero-Diels-Alder reactions. The function of the partially reduced binaphthyl skeleton, however, can sometimes be disadvantageous or ambiguous as illustrated in reactions such as asymmetric ring-closing metathesis, 1,4-conjugate addition, epoxidation, allylic alkylation, trimethylsilylcyanation, epoxide ring-opening and hydroformylation.