Differentially protected benzenediboronic acids: divalent cross-coupling modules for the efficient synthesis of boron-substituted oligoarenes

On the basis of the boron-masking strategy, new divalent cross-coupling modules have been designed for the efficient synthesis of boron-substituted oligoarenes. The modules, i.e., monoprotected o-, m-, and p-benzenediboronic acid derivatives, undergo highly selective Suzuki-Miyaura coupling with sp2 iodides, bromides, chlorides, and triflates, affording coupling products in which the protected boronyl groups are left intact.     

In situ measurements of the dynamics of single giant DNA molecules at the toluene-trioctylamine/water interface by total internal reflection fluorescence microscopy

The dynamics of single giant deoxyribonucleic acid (T4GT7DNA, 165 600 base pairs) molecules was examined near and at the toluene/water, toluene-trioctylamine mixtures/water, and trioctylamine/water interfaces by total internal reflection fluorescence microscopy. The results were considerably affected by the trioctylamine content. With pure toluene or mixtures of lower trioctylamine volume contents (%VA), the randomly coiled DNA molecules diffused to near the interfaces. With mixtures of higher %VA (9 and 50%), the DNA molecules were stretched and adsorbed at the interfaces. There are a large number of anionic phosphate groups ((-O)2PO2-) in the DNA molecule that have an electrostatic affinity to protonated trioctylamine existing at the interface. In the case of pure trioctylamine, globular DNA molecules were adsorbed at the interface and also existed in the aqueous phase.     

Synthesis,chiral resolution and optical properties of amphiphilic oxa[9]helicene derivatives

A new class of amphiphilic oxa[9]helicene derivatives were synthesized in excellent-to-fair yields, and successfully characterized by different analytical techniques (e.g., FT-IR, ¹H and ¹³C NMR, and HRMS). The compounds were enantiomerically separated by chiral HPLC and the absolute configurations of the enantiomers were confirmed by circular dichroism spectroscopy. Other optical properties (e.g., UV, photoluminescence, specific optical rotation and molecular optical rotation) of the newly synthesized compounds were also examined.     

Mechanocaloric properties of poly(dimethylsiloxane) and ethylene–propylene rubbers

We measured the temperature change in strips of poly(dimethylsiloxane) (PDMS) and ethylene–propylene rubbers that occurred as they were stretched and allowed to shrink by a factor of 3.5–4.5, along with the tensile force that effected the deformation. Main results obtained are as follows: (1) the temperature change is fully reversible in E–P rubber and slightly but definitely irreversible in PDMS rubber. The temperature rise in the latter on stretching is larger than the fall on shrinking by ca. 20 %. (2) The reversible part of heat that evolves from or is absorbed by PDMS rubber is smaller than, but close to, the mechanical energy expended. For E–P rubber, the heat generated greatly exceeds the expended mechanical energy. (3) The entropy of extension as a function of extension is reproduced well by Wang and Guth calculation for PDMS rubber, but not for E–P rubber.     

A Novel Synthesis of Selenides and Selenol Esters Using Liquid-Liquid Phase-Transfer Catalysis

This article describes the first attempt to synthesize selenides and selenol esters prepared from the reaction of 1-benzyl or 1-acylselenophenylmethaniminium halides and organic halides under liquid-liquid phase-transfer conditions. This method also can be applied to the synthesis of diseleno tweezers-like molecules as metalloreceptors.     

2-Sulfanylhydroquinone Dimer as a Switchable Fluorescent Dye

A new dye was developed, the photoluminescence properties of which are controlled by a chemical reaction. The fluorescence properties of 2-sulfanylhydroquinone dimers depend on the number of hydroxyl groups that are acylated. Unprotected or monoacylated 2-sulfanylhydroquinone dimers displayed good fluorescence properties, whereas diacylated and tetraacylated 2-sulfanylhydroquinone dimers showed dramatically decreased fluorescence. A monomesylated derivative was devised, which shows good fluorescence characteristics as a switching fluorescence dye through a chemical reaction.     

Predicting experimental yields as an index to rank synthesis routes: application for Diels-Alder reactions

It is possible to create novel synthetic routes for compounds using synthesis route design systems (SRDS). We have been investigating an in silico screening protocol, which makes it possible to reduce the number of SRDS experiments in developing new synthesis routes. However, there still remains the problem of how to rank synthesis routes for experiments. The experimental yield is considered to be one of the most important factors in determining which synthesis route is better. The present study describes an attempt toward predicting the trends of experimental yields for organic synthesis by fusing computational chemistry and chemoinformatics. We examined whether the prediction of experimental yields for Diels-Alder reactions is feasible using activation energies obtained from Density Functional Theory (DFT) calculations together with the experimental conditions. A partial least squares analysis using these values gave correlation equations for the experimental yields. If it is possible to construct similar correlation equations for other reactions, then SRDS synthetic routes could be ranked on the basis of their predicted yields, and an order can be determined before beginning the experiments.     

Syntheses and Fully Diastereospecific Photochromic Reactions of Thiophenophan‐1‐enes with Chiral Bridges

Thiophenophan‐1‐enes with chiral polyether bridges were prepared and their diastereospecific photochromic reactions were studied. The coupling reaction of substituted dithienylethenes and various chiral synthons afforded thiophenophan‐1‐enes, namely, bridged dithienylethenes, as single enantiomers without optical resolution, thus indicating that these reactions occurred diastereoselectively. Upon UV irradiation, each optically active thiophenophan‐1‐ene isomerized to the corresponding enantiomer of the closed form and returned to the initial enantiomer of the open form upon visible irradiation. Because thiophenophan‐1‐enes never isomerized to other diastereomers even at a high temperature, they underwent diastereospecific photochromic reactions. Large changes were observed in the measurement of the optical rotations of the solutions of thiophenophan‐1‐enes at 588 nm according to their photochromic reactions. As there was no absorption at this wavelength for both isomers of each thiophenophan‐1‐enes, the nondestructive readout of the photochromic reaction could be carried out by using these chiral thiophenophan‐1‐enes.     

Rhodium-catalyzed organothio exchange reaction of α-organothioketones with disulfides

RhH(PPh(3))(4) and 1,2-bis(diphenylphosphino)ethane (dppe) catalyzed the organothio exchange reaction of α-organothioketones and organic disulfides. The reaction was affected by the structure of the substrate: α-phenylthio and α-alkylthio aryl ketones reacted effectively with diaryl and dialkyl disulfides; α-phenylthio dialkyl ketones reacted with diaryl disulfides but not with dialkyl disulfides; diaryl disulfides with electron-donating p-substituents were more reactive than those with electron-withdrawing p-substituents.     

Towards the development of synthetic routes using theoretical calculations: an application of in silico screening to 2,6-dimethylchroman-4-one

This study describes an attempt to develop a synthetic route using theoretical calculations, i.e., in silico synthesis route development. The KOSP program created four potential synthetic routes for generating 2,6-dimethylchroman-4-one. In silico screening of these four synthetic routes was then performed. In silico screening involves theoretical analysis of synthetic routes prior to actual experimental work. A synthetic route using the Mitsunobu reaction had already been reported by Hoddgets et al. Theoretical investigations were also conducted on two S(N)Ar reactions as well as a Michael reaction before they were examined experimentally. In silico screening using DFT calculations indicated that only the Michael reaction was likely to produce the target. Experimental work confirmed that the target was obtained in a yield of 76.4% using the Michael reaction. The other two routes, except for the Mitsunobu reaction, failed to generate the target. Our results demonstrate that theoretical calculations can be used to narrow down the number of experiments that need to be conducted when developing novel synthetic routes.