Asymmetric catalysis with 7-ring chelate diphosphines: DIOP, BINAP and conformational mobility

Rhodium-Catalyzed Asymmetric Hydrogenation of 3-Benzoylaminocoumarins for the Synthesis of Chiral 3-Amino Dihydrocoumarins

An asymmetric hydrogenation of 3-benzoylaminocoumarins was achieved for the first time using our BridgePhos-Rh catalytic system, providing chiral 3-amino dihydrocoumarins in high yields (up to 98 %) and with excellent enantioselectivities (up to 99.7 % ee). The relationship between the enantioselectivities of the hydrogenations and the dihedral angles and the resulting π-π stacking effects of the BridgePhos-Rh complexes, which were determined by X-ray diffraction analysis, are discussed. The corresponding hydrogenated products allow for many transformations, providing several chiral skeletons with important physiological and pharmacological activities.

Stereochemistry, Stereodynamics, and Redox and Complexation Behaviors of 2,2'-Diaryl-1,1'-Biazulenes

2,2'-Diaryl-1,1'-biazulenes were synthesized and electronic communication between the azulene subunits was suggested based on redox measurements. The linkage of azulene at the 1-position also appeared to increase the HOMO levels. In addition, cyclic voltammetry measurements of 2-arylazulenes showed a return peak associated with the oxidation, which was not observed for azulene. The stabilization of the single-electron oxidant may be due to the SOMO-HOMO energy inversion phenomenon. X-ray crystallography of the azulene dimers revealed that this species possessed a syn-type structure in which both aryl groups in the 2-positions formed π-stacks. The twisted structure was indicated to be in the (R)- or (S)-configuration for all molecules in the unit cell. Spontaneous resolution was also shown. Furthermore, from the solid circular dichroism (CD) spectral measurements, the relationship between the absolute configuration of the molecules and the CD spectra was determined. A racemization rotational barrier of ca. 27 kcal mol^-1 was calculated. Moreover, the pyridylazulene dimer cyclized upon reaction with PdCl₂ to form a 3 : 3 complex, in which the biazulene units cyclized to give ratios between the (R)- and (S)-forms of either 2 : 1 or 1 : 2.

C-H Activation in Primary 3-Phenylpropylamines: Synthesis of Seven-Membered Palladacycles through Orthometalation. Stoichiometric Preparation of Benzazepinones and Catalytic Synthesis of Ureas

The dimeric cyclometalated complexes [Pd2{κ(2)C,N-C6H4CH2CH2C(R)(Me)NH2-2}2(μ-Cl)2] (R = Me (1a), H (1b)) are prepared by reacting 1,1-dimethyl-3-phenylpropylammonium or 1-methyl-3-phenylpropylammonium triflate with Pd(OAc)2 in a 1:1 molar ratio and subsequent treatment with excess NaCl. The mononuclear derivatives [Pd{κ(2)C,N-C6H4CH2CH2C(R)(Me)NH2-2}Cl(L)] (L = PPh3, R = Me (3a), H (3b); L = 4-picoline (4-pic), R = Me (4a), H (4b)) were prepared from 1a,b by splitting the chloro bridges with the neutral ligands L. A conformational analysis of the mononuclear palladacycles in solution has been carried out. Insertion of CO takes place into the Pd-C bond of complexes 1a,b, affording Pd(0) and the tetrahydro-benzazepinone 5a or 5b, which possesses potential pharmacological interest. Additionally, the triflate salt A or B undergoes catalytic carbonylation with CO to afford the corresponding N,N'-dialkylurea, using Pd(OAc)2/Cu(OAc)2, in boiling acetonitrile. The crystal structures of 3a·(1)/2H2O, 3b, 4b·CHCl3, and 5a were determined by X-ray diffraction studies.