Daniel Chávez

Asymmetric Transfer Hydrogenation of Prochiral Ketones in Aqueous Media with Chiral Water-Soluble and Heterogenized Bifunctional Catalysts of the RhCp*-Type Ligand

Asymmetric transfer hydrogenation (ATH) of prochiral aromatic ketones was carried out with a water-soluble complex of Rh(III)Cp* and mononitrobenzenesulfonamide bidentate ligand (1R,2R)-N-(2-aminocyclohexyl)-4-nitrobenzenesulfonamide 1 derived from chiral cyclohexane-1,2-diamine. Aqueous sodium formate was used as the hydride source. The reaction afforded the chiral alcohols in good enantioselectivities (79-93%) and yields (>99%). The modified monosulfonamide ligand was also covalently immobilized on solid phase such as silica, resin, and mesoporous SBA-15 silica and then explored as a catalyst with Rh(III)Cp* in the ATH of acetophenone.

Asymmetric transfer hydrogenation of ketones in aqueous solution catalyzed by rhodium(III) complexes with C2-symmetric fluorene-ligands containing chiral (1R,2R)-cyclohexane-1,2-diamine

Dois ligantes C2-simetricos bis(sulfonamide) contendo o fluoreno-quiral (1R,2R)-ciclohexano-1,2-diamina foram complexados com RhIII(Cp*) e usados como catalizador para reducao aromatica de cetonas. Os alcoois secundarios correspondentes foram obtidos com ee 87-100% e rendimento de 85-99%, sob condicoes de transferencia de hidrogenio assimetrica (THA), usando formato de sodio aquoso como fonte de hidretos. Usando acetofenona, obteve-se ee de 94% e rendimento de 86-97%, com uma razao substrato/catalizador de 10.000.

Synthesis of Chiral Aromatic Alcohols: Use of New C2-Symmetric RhIIICp∗, RuII(cymene), or RuII(benzene) Complexes Containing Chiral Diaminocyclohexane Ligand as Asymmetric Transfer Hydrogenation Catalyst

Abstract Twelve chiral secondary alcohols were synthesized by asymmetric transfer hydrogenation (ATH) using C2-symmetric bis(sulfonamide) ligand (2) derived from (1R,2R)-cyclohexane-1,2-diamine and complexed with [RhCl2Cp*]2, [RuCl2(cymene)]2, or [RuCl2(benzene)]2 and then used in situ in the reduction of prochiral ketones. The alcohols were obtained in 85–99% yield and 90–99% enantioselectivity with isopropanol as the hydrogen source. Two-fold rate enhancement and better yields were achieved (88–99%) with 80–99% enantioselectivity using the complex [RhCl2Cp*]2 and aqueous sodium formate as the hydrogen source.

A Novel and Highly Regioselective Synthesis of New Carbamoylcarboxylic Acids from Dianhydrides

A regioselective synthesis has been developed for the preparation of a series of N,N′-disubstituted 4,4′-carbonylbis(carbamoylbenzoic) acids and N,N′-disubstituted bis(carbamoyl) terephthalic acids by treatment of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (1) and 1,2,4,5-benzenetetracarboxylic dianhydride (2) with arylalkyl primary amines (A-N). The carbamoylcarboxylic acid derivatives were synthesized with good yield and high purity. The specific reaction conditions were established to obtain carbamoyl and carboxylic acid functionalities over the thermodynamically most favored imide group. Products derived from both anhydrides 1 and 2 were isolated as pure regioisomeric compounds under innovative experimental conditions. The chemo- and regioselectivity of products derived from dianhydrides were determined by NMR spectroscopy and confirmed by density functional theory (DFT). All products were characterized by NMR, FTIR, and MS.

4-Hy­droxy-6-methyl­pyridin-2(1H)-one

In the crystal structure of the title compound, C6H7NO2, N—H⋯O and O—H⋯O hydrogen bonds link the molecules, forming a zigzag array along [001] and a layer structure parallel to the ab plane.

Improved Method for Microwave-Assisted Synthesis of Benzodiazepine-2,5-diones from Isatoic Anhydrides Mediated by Glacial Acetic Acid

1 H NMR (200 MHz, DMSO-d6) δ 3.58 (d, 2H, J 5.6 Hz, CH2), 7.10 (brd, 1H, J 8.0 Hz, H-9), 7.21 (ddd, 1H, J 8.0, 8.0, 1.2 Hz, H-7), 7.51 (ddd, 1H, J 8.0, 8.0, 1.6 Hz, H-8), 7.75 (dd, 1H, J 8.0, 1.6 Hz, H-6), 8.57 (t, 1H, J 5.6 Hz, NH-4), 10.37 (s, 1H, NH-1); 13 C NMR (50 MHz, DMSO-d6) δ 49.5, 126.0, 129.0, 130.6, 135.9, 137.4, 142.2, 173.2, 176.2; EIMS m/z (rel. int. %): [M] + 176 (100), 147 (51), 119 (54), 92 (34). The spectroscopic data are in agreement with those reported in the literature. 1-3

A Novel Synthesis of 1,2,3-Benzotriazinones from 2-(o-Aminophenyl)oxazolines

1,2,3-Benzotriazinones were synthesized in excellent yields by the reaction of 2-(o-aminophenyl)oxazolines and isoamyl nitrite in methanol. The crystal structure of the acetyl derivative of one of the 1,2,3-benzotriazinones provided additional support for the spectroscopic structural characterization of the title compounds.

N-{1,2-Bis(pyridin-3-yl)-2-[(E)-(pyridin-3-yl)methyl­idene­amino]­eth­yl}nicotinamide

In the title compound, C24H20N6O, the pyridin-3-yl groups on the ethylene fragment are found in a trans conformation with a C(py)—C(e)—C(e)—C(py) (py = pyridine, e = ethylene) torsion angle of 179.2 (3)°. The dihedral angle between the pyridine rings is 3.5 (1)°. In the crystal, N—H⋯N and C—H⋯O=C interactions form a layer arrangement parallel to the bc plane. The compound displays disorder of the ethylene fragment over two positions with an occupancy ratio of 0.676 (7) to 0.324 (7) that extends into the amide section of the nicotinamide moiety.