C–H (hetero)arylation of aromatic compounds using transition-metal catalysts has garnered much attention from the synthetic chemistry community as a next-generation coupling method for constructing (hetero)biaryl motifs. This account describes our recent achievements in transition-metal-catalyzed aromatic C–H arylation and its applications to the synthesis of bioactive molecules.
The reaction of (Me4N)4[Cd10S4(SPh)16] (1) with diphenyl diselenide (2) in propionitrile afforded a molecular cluster, (Me4N)4[Cd10S4(SePh)16] (3), the structure of which was determined by X-ray crystallography. Ligand exchange proceeded in a heterogeneous reaction system, and the use of a less polar solvent appeared to be crucial for the synthesis of 3 to prevent degradation of the Cd10S4Se16 cluster core.
A macrocyclic compound 1 with two butadiyne and four dodecyloxy-substituted benzamide moieties was successfully synthesized, and its ring structure was confirmed by the MALDI-TOF mass spectra and the 1H NMR spectra. Compound 1 showed two modifications depending on solvent for the solidification. Characteristic excitonic absorption bands of polydiacetylene were observed at around 500 nm for one of the modifications after UV irradiation. Quantitative conversion of butadiyne moieties to the corresponding polydiacetylene structure was confirmed by the Raman spectra.
An umpolung N-alkylation reaction of β,γ-alkenyl α-iminoesters was studied, and various tandem reactions were found utilizing this N-alkylation. A useful synthesis of δ-lactones and dienamines was developed by tandem N-alkylation/vinylogous aldol-type reaction. The synthesis of α-quaternary alkenyl amino esters was also developed via the tandem N-alkylation/bromination/C-alkylation. These methods using β,γ-alkenyl α-iminoesters are operationally simple and useful, and exhibit broad substrate generality.
Focused 1064-nm laser beam irradiation to an aqueous 1-butanol (BuOH) solution (7.1–7.4 wt % in H2O) resulted in formation of a single picoliter-volume BuOH droplet. Since water (H2O) absorbs 1064-nm laser light, an aqueous BuOH solution at the laser beam focus is heated via photo-thermal effects and this leads to thermal phase separation of the solution, producing a single BuOH microdroplet. In the presence of a fluorescent dye (10−5–10−7 mol/dm3) in an aqueous BuOH solution, the dye was extracted from the surrounding water phase to the BuOH droplet produced by laser irradiation as demonstrated by in situ fluorescence and Raman microspectroscopies. The present laser-induced water-to-single microdroplet extraction/detection was also extended successfully to that under pressure-driven and electroosmotic flow conditions in microflow devices. In both cases, the single BuOH microdroplets produced by 1064-nm laser irradiation were optically trapped against flow of the solution. Under electroosmotic flow conditions, highly sensitive detection of a fluorescent Al3+-chelate complex injected to an electrophoresis capillary tube was also achieved successfully by single BuOH microdroplet formation and simultaneous extraction of the Al3+ chelate to the droplet by 1064-nm laser irradiation.
The reproducibility of higher-order derivative spectra of aqueous solutions of N-methyl-4-(p-formylstyryl)pyridinium salt (FSbQ) as a model compound were examined by the conversion of UV–vis absorption spectra taken on six spectrophotometers into derivatives with aid of software for data analysis as a common tool for differentiation and smoothing. The spectral shapes of crude fourth and eighth derivatives were not only quite noisy, but also considerably dependent on the spectrophotometers. Savizky–Golay smoothing under the same and appropriate conditions, however, provided satisfactorily identical derivative-spectra, confirming the reproducibility of derivative spectroscopy. In order to reveal the reliability of the quantitative analysis on the basis of Beer’s law, absorbances (A) of aqueous solutions of FSbQ were plotted against dnA/dλn (Dn) values at subpeaks of the fourth as well as eighth derivatives. Excellent linearity between A and Dn was disclosed when A is smaller than ca. 1, leading to the confirmation that Dn values are usable for kinetic studies on the photoisomerization of FSbQ as an example.
Indene-2-carboxylic acids are prepared from allenylbenzenes and CO2 by an AlBr3-mediated tandem reaction consisting of intramolecular Friedel–Crafts alkylation of allenylbenzenes and subsequent carbonation of the resulting indenylaluminum species. The reaction requires 2,6-di-tert-butylpyridine or 2,6-diiodopyridine to neutralize an acidic by-product without deactivating the Lewis acid.
A new empirical linear relation between the enthalpy of vaporization and (Tc − Tm) (Tc: critical temperature, Tm: melting temperature) is presented for liquids of similar chemical groups. Combination of the above finding with Trouton’s rule leads to another linear relation between Tb (boiling temperature) and (Tc − Tm). As an extension, a different expression for the Guldberg rule is also derived. These findings can contribute to the understanding of general behavior of liquids and the development of theories of liquids.
Cofacial dimers of porphyrin and/or phthalocyanine are plausible frameworks for functional molecular systems such as molecular catalysts and molecular memories. We recently developed a supramolecular array of a porphyrin and phthalocyanine linked by a four-fold rotaxane. In this study, we demonstrated programmable hetero-ion arrangement in the heterodimer of these tetrapyrrolic ligands. Ni(II) and Fe(II) ions showed kinetically selective binding to the porphyrin, whereas Mn(II) ions selectively bound to the phthalocyanine, in the supramolecular array. After the first metal complexation, subsequent metal insertion into the vacant ligand afforded the programmed heterodinuclear complex. Moreover, the metal arrays were extended to heterotrinuclear complexes via ionic pairing of the cationic four-fold rotaxane with a tetraanionic metalloporphyrin.
The bioassay-guided fractionation of the Okinawan marine cyanobacterium Okeania sp. led to the isolation of the novel cyclodepsipeptide odobromoamide (1). The gross structure of 1 was determined by spectroscopic analyses, and its absolute stereochemistry was determined using a variety of different methods, including chemical derivatization and degradation followed by HPLC analysis. In addition, odobromoamide (1) exhibited broad-spectrum cytotoxicity against a human cancer cell line panel.
A series of D–π–A dyes (AK1–5) was designed and synthesized for applications in dye-sensitized solar cells (DSSCs). AK1–5 contain triphenylamines as electron donors (D), bithiophene π-spacers, boryl-substituted thienylthiazole as electron acceptors (A), and carboxylic acid derivatives as anchor groups. Electrochemical and photophysical measurements on AK1–5 revealed that the use of boryl-substituted thienylthiazole moieties with intramolecular B–N coordination bonds effectively increases the electron-accepting ability of such dyes. The electronic effects of the substituents on the boron center, as well as those of the anchor group enable fine-tuning of the LUMO level, which leads to red shift of the absorption bands of these dyes. Subsequently, DSSCs based on AK1–5 were fabricated, and their performance was examined in terms of the relationship between their electronic structure and the absorption range for photon-to-electricity conversion.
Accurate condensed-phase quantum chemical calculations employing the continuum cluster model were undertaken to systematically examine the reactivity of amine solvents with CO2, a reaction of great importance in CO2 capture and storage technologies. Thirteen amine compounds, including primary, secondary, tertiary, and hindered amines, were considered, and up to ten solvent water molecules were modeled explicitly including continuum solvation. Amine pKa values and reaction Gibbs energies for the formation of bicarbonate, carbamate, and zwitterions were evaluated. Our calculations indicate that increasing the number of explicit water solvents (n) steadily improves computational accuracy, reducing the mean absolute deviation (MAD) of the calculated pKa from the experimental values, i.e., 13.0, 8.6, 1.3, and 0.9 (in pKa units) at n = 0, 1, 6, and 10, respectively. Reaction Gibbs energies calculated with large n for the studied reactions were consistent with the experimental observation that carbamates are the most stable product species, although their stability is lower for secondary amines. However, at n = 0 or 1, positive reaction Gibbs energies were predicted, suggesting that bicarbonate formation would not occur. These results strongly indicate that the trend in the reactivity of CO2-amine reactions can only be correctly predicted by modeling solute-solvent interactions accurately.