Binaphthyl ligands asymmetric reactions

Buchwald has designed a hindered dialkylphosphino-binaphthyl ligand (3) that is much more active than the original ligand for asymmetric arylation of ketone enolates. Reactions occur at room temperature using only 2 mol % catalyst with enantioselectivities up to 94% [41]. Additionally, the Buchwald group has developed an electron-rich monodentate ligand (4) capable of vinylation of ketone enolates with up to 92% ee [42]. 

The enantiomeric atropoisomers of 1,1 -binaphthyl-2,2 -diol (BINOL) and bis-diphenylphosphonate derivatives (BINAP) are completely synthetic molecules that have been developed to exploit the axial dissymmetry induced by the restricted rotation about the biaryl bond (Scheme 1.8) [64]. During the past 15 years, these compounds have become the most widely used ligands for both stoichiometric and catalytic asymmetric reactions, with many analogues and derivatives having been developed recently. 

Optically active l,l -binaphthols are among the most important chiral ligands of a variety of metal species. Binaphthol-aluminum complexes have been used as chiral Lewis acid catalysts. The l,T-binaphthyl-based chiral ligands owe their success in a variety of asymmetric reactions to the chiral cavity they create around the metal center [107,108]. In contrast with the wide use of these binaphthyls, the polymer-supported variety has been less popular. The optically active and sterically regular poly(l,l -bi-naphthyls) 96 have been prepared by nickel-catalyzed dehalogenating polycondensation of dibromide monomer 95 (Sch. 7) [109] and used to prepare the polybinaphthyl aluminum(III) catalyst 97 this had much greater catalytic activity than the corresponding monomeric catalyst when used in the Mukaiyama aldol reaction (Eq. 29). Unfortunately no enantioselectivity was observed in the aldol reaction. 

The similar reaction of diarylphosphine oxides with aryl halides and triflates has been used more recently to prepare a variety of ligands for asymmetric catalysis. Many of these reactions involve additions of secondary phosphine oxides to di- or monotriflates derived from binaphthol because the triflates are more accessible than 2,2 -l,l -dibro-mobinaphthol. Workers at Syntex described a procedure to use the ditriflate of binaphthol to prepare mixed phosphine oxide, hydroxo ligands, and the monophosphine oxide, bi-naphthyldiphenylphosphine oxide. Hayashi then developed a route to a number of chiral monodentate phosphine ligands with a 2-(diphenylphosphino)-2 -alkoxy-l,l -binaphthyl structure (Eq. Reaction of the ditriflate with diphenylphosphine oxide in the... 

The Diels-Alder reaction has not escaped the attention of chemists interested in asymmetric synthesis. A binaphthyl-based chiral aluminium complex (30) catalyses the hetero Diels-Alder cycloaddition between benzaldehyde and the Danishefsky diene (29), providing the dihydropyrone (32) with excellent selectivity after acid hydrolysis of the initial adduct (31). 0 2] (We will see further applications of chiral binaphthyl ligands in section 6.4.)... 

Tamao. K.. H. Yamamoto. H. Matsumoto, N. Miyake, T. Hayashi, and M. Kumada Optically Active 2.2 -Bis-(diphenylphosphinomethyl)-l,r-binaphthyl A New Chiral Bidentate Phosphine Ligand For Transition-Metal Complex Catalyzed. Asymmetric Reactions. Tetrahedron Letters 1977, 1389. 

Saha B, RajanBabu TV (2007) Syntheses and applications of 2-phosphino-2 -aIkoxy-l,l -binaphthyl ligands. Development of a working model for asymmetric induction in hydrovinyiation reactions. J Org Chem 72 2357-2363... 

The MOP range of ligands designed by Hayashi has proved remarkably useful for asymmetric hydrosilylation reactions.59 MOP ligands are a series of enantiomerically pure monophosphine ligands whose chirality is due to 1,1 -binaphthyl axial chirality. 

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