NORPHOS

Recently, a series of chiral diphosphines (S. -Me-Duphos, (S. -chiraphos, (R,R)-diop and (+)-Norphos were grafted after an ionic exchange onto Al-MCM-41 134 complexes of the form [Rh(cod)(diphosphine)]+ were tested for the hydrogenation of dimethylitaconate. The supported complex with (S,S)-methyl-Duphos reached an activity for the formation of dimethyl ( -methyl-succinate as high as TON = 4000 with an ee close to 92%. Both (R,R)-diop and (,S S )-chiraphos give lower enantioselectivities (ee = 34% and 47% respectively). With (+)-Norphos, dimethyl-([Pg.457]

The highly enantioselective reductive animation of a-keto acids as a route to amino acids is possible with ligand 118 (3 R,4R)- l-W-benzyl)-3,4-bis(diphenylphosphanyl)pyrrolidine, DEGUPHOS] and [Rh(cod)2]BF4.649 (R,R)-NORPHOS (2-exo-3-endo-bis(diphenylphosphino)bicyclo[2.2.1 ]heptene) and (2. S, 3. S ) - C HIR AP H O S (bis(diphenylphosphino)butane) are also good ligands for this transformation. Arylpyruvic acids give the best results (>95% ee). 

Iridium(III) hydride forms complexes with DIOP, BDPP (2,4-bis(diphenyl-phosphino)pentane), NORPHOS, and BINAP ligands to produce amines in 11 -80% ee.679 Similar modest results are obtained in the reduction of N-arylketimines with an iridium(HI) complex with (2S,3 S) -C HIRA PHOS as the chiral ligand.680 The indium complexes with chiral phosphinodihydrooxazoles catalyze the enantioselective hydrogenation of imines in supercritical carbon dioxide with up to 80% ee, but generally lower ee values are observed in... 

More recent work employing diphosphine ligands has focused on both new substrates for hydroboration and also new hydroborating agents. Specifically, Gevorgyan has successfully employed cyclopropenes 56 as substrates, with pinacolboranes 13 as the borane source.20 Impressive enantioselectivities were obtained with a range of diphosphines, for example, with rhodium complexes of NORPHOS (>99% ee), PHANEPHOS (97% ee), BINAP (94% ee), and Tol-BINAP (96% ee), all with near perfect m-selectivity (see Scheme 8). 

Norton and coworkers found that catalytic enantioselective hydrogenation of the C=N bond of iminium cations can be accomplished using a series of Ru complexes with chiral diphosphine ligands such as Chiraphos and Norphos [68], Even tetra-alkyl-substituted iminium cations can be hydrogenated by this method. These reactions were carried out with 2 mol.% Ru catalyst and 3.4—3.8 bar H2 at room temperature in CH2C12 solvent (Eq. (39)). 

The electronic properties around the phosphorus atom can be varied by manipulation of the groups on that atom. MOD-DIOP (12c) was developed by Achiwa and used to reduce itaconic acids [68-72, 75, 103]. Some variations built on BCPM (18e), itself a variant of BPPM, such as the MOD-BCPM (18f) and MCCPM (18g) [88-93, 95-98, 104]. Other variants are PYRPHOS (21a also called DeguPHOS) [105, 106], DPCP (22) [107], NorPhos (23) [108], BDPP (24a) (also called SkewPHOS) [109-111], and PPCP (25) [112]. 

Some developments have been carried out for the enantioselective synthesis of biologically active compounds. One such example is the synthesis of ethyl (R)-2-hydroxy-4-phenylbutyrate, an important intermediate for the angiotensinconverting enzyme (ACE) inhibitor benazepril, or for coenzyme A, using the NORPHOS ligand (Scheme 33.9) [21]. 

Recently, Borner and coworkers described an efficient Rh-deguphos catalyst for the reductive amination of a-keto acids with benzyl amine. E.e.-values up to 98% were obtained for the reaction of phenyl pyruvic acid and PhCH2COCOOH (entry 4.9), albeit with often incomplete conversion and low TOFs. Similar results were also obtained for several other a-keto acids, and also with ligands such as norphos and chiraphos. An interesting variant for the preparation of a-amino acid derivatives is the one-pot preparation of aromatic a-(N-cyclohexyla-mino) amides from the corresponding aryl iodide, cyclohexylamine under a H2/ CO atmosphere catalyzed by Pd-duphos or Pd-Trost ligands [50]. Yields and ee-values were in the order of 30-50% and 90 >99%, respectively, and a catalyst loading of around 4% was necessary. 

Asymmetric coupling of a vinyl halide with a Grignard reagent. 1-Phenylethyl-magnesium chloride couples with vinyl bromide in the presence of a nickelcatalyst (1) composed of NiCl, and (-)-norphos to give (S)-3-phenyl-l-butene (2) in 67% enantiomeric excess.1... 

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