P-Chiral Phosphine Ligands for Transition-Metal-Catalyzed Asymmetric Reactions

Abstract

: Optically active phosphine ligands possessing stereogenic centers on phosphorus atoms have been synthesized using phosphine-boranes as intermediates. Electron-rich P-chiral phosphine ligands (BisP*, MiniPHOS, and DiSquareP*) having a bulky alkyl group and a small alkyl group on the phosphorus atom exhibit excellent to almost perfect enantioselectivities in the Rh-catalyzed asymmetric hydrogenation of enamides and related substrates. Air-stable P-chiral phosphine ligands (t-Bu-and 1-Ad-QuinoxP*) are also prepared with the phosphine-borane methodology. These ligands have exceedingly high enantioselectivities of up to 99.9% not only in Rh-catalyzed asymmetric hydrogenation but also in Rh-or Pd-catalyzed carbon-carbon bond-forming reactions.Catalytic asymmetric synthesis is one of the most efficient methods for the production of optically active compounds. Among various asymmetric catalyses, transition-metal-catalyzed reactions have attracted a great deal of attention over the years; many catalyst systems of this class have been developed and some have been successfully applied to the industrial production of useful optically active compounds.1 Both enantioselectivity and catalytic efficiency are highly dependent on chiral ligands and central metals. Therefore, the design and synthesis of new chiral ligands is a very important research subject in this field.2Among various types of chiral ligands, phosphine ligands are the most frequently employed, owing to their inherent ability to coordinate strongly to transition metals and to promote catalytic reactions. Hence, numerous optically active phosphine ligands have been synthesized and used in tiansition metal catalyses.3 Chiral phosphine ligands reported so far are classified roughly into two types. One type is phosphines having asymmetric carbon atoms or backbone chirality. Representative examples of this type are shown in Figure 1. The stereochemical feature of this type is that the two substituents on the phosphorus atoms are diastereotopic and are capable of forming an asymmetric environment around the reaction center.The other type is the so-called P-chiral phosphine ligands, that possess stereogenic centers on the phosphorus atoms themselves. Figure 2 shows methylphenylpropylphosphine (1),4a,b CAMP (2),4c and DIPAMP (3),4d-g which are representative P-chiral phosphine ligands. These ligands played very important roles early on in the history of homogeneous asymmetric hydrogenation.4 Nevertheless, only a small number of P-chiral ligands were reported in the two decades following 1976, mainly because of the lack of efficient methods for the preparation of optically pure P-chiral phosphines, and the anticipation that some phosphines of this class are stereochemically unstable and gradually racemize via pyramidal inversion even at room temperature.5CAMP (2) DIPAMP (3) In a previous study of the synthesis and reactions of phosphine-boranes, we found that optically active P-chiral phosphine ligands could be synthesized using phosphine-boranes as intermediat...

Recent progress in the development of advanced element-block materials

“…110 Therefore, their complexes are widely used as chiral catalysts. [111][112][113] There are several optically active polymers whose structures are highly controlled by repeating asymmetric reactions; however, optically active polymers including chiral heteroatoms in the main chain are limited. In our group, we have successfully reported oligomers, [114][115][116][117] polymers, 118-123 dendrimers 124 and macrocycles, [125][126][127][128][129][130][131][132][133] including chiral phosphorus atoms in the main chain, and we have revealed their properties and potential applications.…”

Enantioselective Hydrogenation Catalysis Aided by a σ-Bonded Calix[4]arene to aP-Chirogenic Aminophosphane Phosphinite Rhodium Complex

“…Asymmetric catalysis using chiral transition metal complexes is a powerful method for the synthesis of chiral substances, in laboratory scale as well as industrially. − So far, mostly chiral catalysts were prepared by complexation of a chiral organophosphorus ligand and a transition metal. , However, improving an asymmetric catalytic reaction for a new substrate is never trivial and is mainly restricted by the availability of a library of chiral ligands or by the structure modification of an efficient lead series such as BINAP, DUPHOS, PHOX, monophos, bisP*, and SDP …”