A highly efficient iridium-catalyzed hydrogenation of alpha,beta-unsaturated carboxylic acids has been developed by using chiral spiro-phosphino-oxazoline ligands, affording alpha-substituted chiral carboxylic acids in exceptionally high enantioselectivities and reactivities.
We present a first-principles density functional theory study focused on how the chemical and electronic properties of polyaniline are adjusted by introducing suitable substituents on a polymer backbone. Analyses of the obtained energy barriers, reaction energies and minimum energy paths indicate that the chemical reactivity of the polyaniline derivatives is significantly enhanced by protonic acid doping of the substituted materials. Further study of the density of states at the Fermi level, band gap, HOMO and LUMO shows that both the unprotonated and protonated states of these polyanilines are altered to different degrees depending on the functional group. We also note that changes in both the chemical and electronic properties are very sensitive to the polarity and size of the functional group. It is worth noting that these changes do not substantially alter the inherent chemical and electronic properties of polyaniline. Our results demonstrate that introducing different functional groups on a polymer backbone is an effective approach to obtain tailored conductive polymers with desirable properties while retaining their intrinsic properties, such as conductivity.
Eight new khayanolides, named thaixylomolins G-N (1-8), two new phragmalins (9 and 10), and two new mexicanolides (11 and 12) were obtained from the seeds of the Trang mangrove plant Xylocarpus moluccensis. The absolute configurations of these limonoids, except for the stereocenter at C-6 of 11 and 12, were assigned by experimental and TDDFT calculated electronic circular dichroism spectra. The khayanolides may be classified into two subclasses, one of which has a C-2 carbonyl and a 3β-acetoxy group, whereas the other possesses a 2β-acetoxy and a C-3 carbonyl function. Khayanolides, rearranged phragmalin-type limonoids, are reported for the first time from plants of the mangrove genus Xylocarpus. The structure of moluccensin J, a known 30-ketophragmalin containing a Δ(8(14)) double bond, was revised to be a khayanolide, named thaixylomolin K. The antiviral activities of the isolates against pandemic influenza A virus (subtype H1N1) were tested by the assay of cytopathic effect inhibition. Three khayanolides, viz., thaixylomolins I, K, and M, exhibited moderate anti-H1N1 activities. The most potent one, thaixylomolin I (IC50 = 77.1 ± 8.7 μM), showed stronger inhibitory activity than that of the positive control, ribavirin (IC50 = 185.9 ± 16.8 μM).
The transition-metal-catalyzed asymmetric hydrogenation reactions attract long-lasting interest from both academic research and industrial production. [1] The development of chiral ligands is the essential impetus for the asymmetric hydrogenation reactions. During the past decades, chiral P, N ligands having both phosphorus and nitrogen atoms as the coordinating groups become popular in the hydrogenation reactions. [2] Generally, molecules with sp 2 nitrogen atoms, such as oxazoline and pyridine, are required for achieving good results for the chiral P, N ligands. Although several phosphine amine ligands containing primary amine moieties have been successfully applied in the highly enantioselective hydrogenation of ketones, [3] to our knowledge, such ligands have not been applied successfully in the asymmetric hydrogenation of olefins. Herein we report the preparation of novel chiral spiro aminophosphine ligands bearing a primary amine moiety 3 (Scheme 1) and their applications in the hydrogenation of a,b-unsaturated carboxylic acids. The iridium complexes 5 derived from the chiral spiro aminophosphine ligands showed unprecedentedly high activity (turnover numbers (TONs) up to 10 000; turnover frequencies (TOFs) up to 6000 h À1 ) and enantioselectivity (94-99 % ee). The primary amine moiety in the catalysts 5 is the key for obtaining high activity and enantioselectivity.Chiral spiro aminophosphine ligands 3 and 4 were easily prepared starting from optically pure 1 (Scheme 1). [4] Palladium-catalyzed cyanation of 1 (step a) followed by LiAlH 4 reduction (step b) afforded ligands 3 in good yield. Ligands 4, which have an N-methyl group, were prepared from 3 through condensation with ethyl chloroformate and LiAlH 4 reduction in one pot (step c). The iridium complexes 5 were prepared by refluxing a mixture of [{Ir(cod)Cl} 2 ], 3 or 4, and NaBAr F in dichloromethane for two hours (step d). Complexes 5 were stable enough to be purified by silica gel column chromatography and stored in air without degradation for a few months. The structure of complex (S a )-5 a was proved by an X-ray diffraction analysis of a single crystal. [5] According to the crystal structure, (S a )-3 a acts as a chelating P, N ligand and creates a rigid chiral pocket around the iridium center.The asymmetric hydrogenation of a-substituted acrylic acids 6 (for structures see Table 2) is of highly practical value because the products, optically pure a-substituted propionic acids, include important biologically active compounds. For example, ibuprofen (7 a) and naproxen (7 f), [6] two wellknown non-steroid anti-inflammatory drugs, can be readily prepared by asymmetric hydrogenation of the corresponding a-aryl acrylic acids. Although chiral ruthenium catalysts usually give high enantioselectivity in the asymmetric hydrogenation of a-substituted acrylic acids, most of these catalysts require high hydrogen pressure (e.g., 100 atm) to achieve complete conversion and high enantioselectivity. [7] The high pressure markedly limits the practical applicatio...
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