Abstract: For the first time the hydrogen bond based structure of self-aggregated Rh-phosphine complexes in fluorinated alcohols was directly determined which gives a rationale for the high enantioselectivity observed in the asymmetric hydrogenation.
Abstract: We herein describe the beneficial effect of fluorinated alcohols on asymmetric hydrogenation using chiral self-assembling rhodium complexes. Previously, the application of these catalysts has been hampered by low reaction rates in nonpolar solvents, which are essential for establishing the self-assembling architecture via hydrogen bonding. Excellent reaction rates are usually observed in alcohols as solvents, but the characteristic hydrogen bonds are cleaved in those media, resulting in poor ee values. We now show for the first time that the disadvantageous properties of both solvent classes on the catalytic reaction can be overcome by using fluorinated alcohols. Due to this key finding, homogeneous catalysis with self-assembling catalysts is much closer to practical application.
Abstract: Three sets of new and related chiral phospholane and phosphepine ligands have been prepared for Rh-catalyzed enantioselective hydrogenation. The size and substitution pattern of the cyclic monophosphanes were varied. More importantly, the ligands differ in
the nature of the heterocyclic group linked to the trivalent phosphorus atom: 2-pyridone or 2-alkoxypyridine. In the corresponding Rh complexes, the pyridone units of two monodentate P ligands can assemble by hydrogen bonding and form chelates. In contrast, synthetic precursors bearing alkoxypyridine appendages are not able to aggregate via intramolecular hydrogen bonds. The nature of self-assembly is dependent on the nature of the P ligand and the solvent used for the hydrogenation (CH2Cl2 vs. MeOH). These features affect the rate of the reaction as well as the enantioselectivity,
which varied in the range of 0–99% ee Complexation studies and DFT calculations
were performed to explain these differences.
Notes: asymmetric catalysis · density functional calculations · hydrogenation · P ligands · rhodium
Abstract: New chiral phospholanes were prepared by coupling of bromo-substituted heterocycles with the enantiopure, building block (2R,5R)-2,5-dimethyl-1-chlorophospholane. Some of the new phosphine ligands have the potential for self-assembling via hydrogen bondings in a metal complex. By application of these and related ligands in the palladium catalyzed allylic amination reaction, high enantioselectivities (up to 99%) were achieved. The influence of the construction of the cyclic phosphine ligands on the enantioselectivity is analyzed.
Abstract: The use of fluorinated alcohols as solvents, cosolvents or additives in homogeneous catalysis is reviewed. The effect of these particular compounds on efficiency, regioselectivity and stereoselectivity of metal-catalyzed reactions, as well as on reactions mediated by organocatalysts, is described. Where available in several cases, the effect of fluorous alcohols on the catalytic mechanism is analyzed in detail and rationalized by their unique physical and chemical properties. In most instances, a comparison to the effect of commonly employed solvents is elaborated.
Abstract: New electron-rich chiral 1,3-diphosphines of the BDPP type were prepared from 1,3-diphenylpropane-1,3-diol by an economically feasible synthetic approach. The r-donor properties of the phosphines were determined by measurement of J(31P–77Se) coupling constants in the corresponding phosphine selenides. For comparison related, but electronically different, 1,3-diphosphines were considered. The new diphosphines showed good enantioselectivities as ligands in the Rh-catalyzed enantioselective hydrogenation of benchmark substrates and b-amino acid precursors (up to 98% ee). The electronic effects on the outcome of the enantioselective catalysis have been analyzed.
Abstract: New chiral aminophosphine phosphinite (AMPP) ligands with different P-aryl substituents were prepared from (1R,3S,4S)-2-azabicyclo[2.2.1]hept-3-ylmethanol by a new and chemoselective synthetic approach. The ligands showed good enantioselectivity (up to 91%) in the Rh-catalyzed enantioselective hydrogenation of benchmark substrates.
Abstract: The enantioselective hydrogenation of 1,3-diarylpropane-1,3-diones with chiral Ru(II)-diphosphine catalyst has been studied. In a first approach it was found, that Tol-BINAP together with Ru(COD)methallyl2 formed the most selective catalyst. One of the C2-symmetric enantiopure 1,3-diols obtained in turn was transformed via its 1,3-di-O-mesylate into 1,3-bisdiarylphosphines. One of them, 1,3-diphenyl-1,3-bis(diphenylphosphino)propane, could be advantageously utilized as a ligand for the efficient enantioselective Ru-catalyzed hydrogenation of its own 1,3-diketone precursor. Thus, the condition for a ‘cross self-breeding’ catalytic system is fulfilled. A further reduction of the preparation costs could be achived by application of RuCl3·H2O instead of other more expensive precatalyst precursors without compromosing the enantioselectivity. The ligand was used in the Rh(I)-catalyzed asymmetric hydrogenation of model substrates and b-amino acid precursors where up to 97% ee could be achieved.
Abstract: A facile multigram scale preparation of (1R,3S,4S)-2-azabicyclo[2.2.1]heptane-3-carboxylic acid via stereoselective
synthesis of the corresponding a-amino ester hydrochloride is detailed. Hitherto applied protocols for the synthesis of this cyclic proline analogue involving a tedious chromatographic purification step could thus be considerably improved upon. The specific rotation of the a-amino acid reported in the literature has been revised.
Abstract: Two chiral -diketones, 1,3-bis[(S)-(4-[2.2]paracyclophanyl)]propane-1,3-dione (BPPD) and [1-(S)-(4- [2.2]paracyclophanyl)-3-phenyl]propane-1,3-dione (PPPD), were synthesized by acylation of (S)-4-acetyl-
[2.2]paracyclophane with methyl esters from the corresponding carboxylic acids. 4-Acetyl[2.2]paracyclophane
was synthesized in a quantitative yield by the reaction of [2.2]paracyclophane-4-carboxylic acid with methyllithium.
Abstract: The synthesis of a series of 4, 4-diacetylaminopiperidines has been achieved by, the reaction of 4-piperidones,
described earlier, with acetonitrile in the presence of concentrated sulfuric acid. The structure and the threedimensional constitution of the compounds has been confirmed by' IR, PMR, and mass spectrometric data.
