Chiral ligands BINAP

Scheme 1.2 Pd-catalysed amination of aryl halides using the chiral ligand Binap.

The chiral ligand BINAP was originally prepared from 2,2 -binaphthol and resolved by complexation with an optically active Pd complex [ 10]. A new method starting from 2-naphthol was developed (Scheme 3.2) [11], In this method optical resolution was achieved at the stage of BINAP dioxide (BINAPO) by using inexpensive optically active acids such as camphorsul-fonic acid and dibenzoyltartaric acid. 

Figure 3.16 The important chiral ligand, BINAP [2,2 -bis(diphenylphosphino)-1, V-binaphthylj, S-enantiomer shown...

Rhodium-catalyzed addition of boronic acids to enone moiety 89 led to a rhodium-enolate 90 which can be trapped by addition to the adjacent carbonyl function giving functionalized cyclopentanes or cyclohexanes 91. An important feature of this methodology is that this process allows the creation of three contiguous stereocenters with a high level of stereoselectivity. An asymmetric version of this reaction has also been realized with a chiral ligand (BINAP) giving excellent enantiomeric excesses (77 to 95%) (Scheme 34). 

Example 9.2 The industrial method for large-scale production of both enantiomers of menthol is based on an asymmetric catalytic reaction in the key step promoted by the Rh(II) complex of the well-known chiral ligand BINAP, available in both enantiomeric forms. This process was developed by Takasago Research Institute, Tokyo, in collaboration with Nobel laureate R. Noyori (Scheme 9.2) [9]. 

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