BINAPS: an axially chiral <i>P</i>,<i>S</i>-heterodonor ligand for asymmetric catalysis based on binaphthalene backbone

The chelating P,S-heterodonor ligand 2-diphenylphosphanyl-1,1¢-binaphthalene-2'-thiol (11) (BINAPS), which features a chiral axis as the unique stereogenic element, has been prepared in both racemic and enantiopure form through a multistep reaction sequence using 2,2'-dihydroxy-1,1'-binaphthalene (BINOL) as the starting material. The reaction sequence is completely stereoconservative and (S)-11 is obtained with no loss of enantiopurity from pure (S)- BINOL. (R)-11 can be alternatively obtained by resolution of racemic 11 using the chiral (S)-benzylaminato Pd(II)- complex 19 as the resolving agent. The S-methyl or the S-i-propyl derivatives 14 have been used as chiral ligands in the Rh(I)-catalyzed asymmetric hydroformylation of styrene and in the hydrogen transfer reduction of acetophenone with modest success (up to 20% ee). In the presence of suitable Pd-complexes the same ligands provide higher ees in the hydrosilylation of styrene (50% ee) and in the allylic alkylation of 1,3-diphenylprop-2-enyl acetate (60% ee)

Synthesis of <i>P</i>,<i>P</i>-heterotopic binaphthyldiphosphanes (BINAPP') devoid of <i>C</i>₂ symmetry from 2,2'-binaphthol

The introduction of two nonequivalent diarylphosphanyl substituents into the 2- and 2'-positions of 1,1'-binaphthalene has been successfully accomplished in four steps from 1,1'-binaphthalene-2,2'-diol (BINOL) through conversion into the ditriflate followed by sequential substitution of triflate groups mediated by palladium or nickel catalysts. The selective monosubstitution of the triflate has been achieved by introducing the first phosphorated substituent in the form of phosphane oxide through a Pd-catalyzed reaction. The otolyl- substituted diphosphane 4c is a chiral inducer that is more efficient than BINAP both in the Rh-catalyzed asymmetric hydrogenation of acetamido acrylic acid derivatives and in the Pd-catalyzed allylic alkylation of 1,3-diphenylprop- 2-enyl acetate (85% ee)