Tetrakis(2-hydroxyphenyl)ethene and derivatives. A structurally preorganized tetradentate ligand system for polymetallic coordination chemistry and catalysis

A topologically unique, conformationally constrained tetradentate ligand system for polymetallic coordination chemistry has been developed: tetrakis(2-hydroxyphenyl)ethene (1a) and substituted derivatives. The design exploits the planarity of the tetraphenylethylene core to impart rigidity to the roughly square oxygen binding array, while maintaining a degree of conformational mobility associated with rotation about the aryl-ethylene carbon-carbon bonds. Tetrakis(2-hydroxyphenyl)ethene derivatives are designed to promote multiple metal bridging over chelating coordination modes. The ligand is synthesized from anisole or 4-tert-butylanisole in four steps via the 2,2'-dimethoxybenzophenone hydrazones 4a,b. The sterically hindered ortho-substituted tetraphenylethylene core is produced in high yield by acid-catalyzed decomposition of the corresponding diaryl diazomethane prepared in situ by oxidation of the hydrazone using nickel peroxide. Deprotection of the methyl ethers using boron tribromide gives tetrakis(2-hydroxyphenyl)ethene (1a), characterized by X-ray crystallography, and tetrakis(5-tert-butyl-2-hydroxyphenyl)ethene (1b). Sterically isolating substituents in the 3-position can be installed via Claisen rearrangement/hydrogenation, providing tetrakis(3-n-propyl-2-hydroxyphenyl)ethene (6) efficiently. To illustrate potential applications of this unprecedented ligand class, two coordination complexes are reported, including tetrakis(2-diethylaluminoxyphenyl)ethene (8), a structurally robust eight-membered-ring aluminum/oxygen crown complex characterized both in solution and in the solid state.     

Mechanism of Mukaiyama-Michael Reaction of Ketene Silyl Acetal: Electron Transfer or Nucleophilic Addition?

Mechanism of Mukaiyama-Michael reaction of ketene silyl acetal has been discussed. The competition reaction employing various types of ketene silyl acetals reveals that those bearing more substituents at the beta-position react preferentially over less substituted ones. However, when ketene silyl acetals involve bulky siloxy and/or alkoxy group(s), less substituted compounds react preferentially. The Lewis acids play an important role in these reactions. Enhanced preference for the more sterically demanding Michael adducts is obtained with Bu(2)Sn(OTf)(2), SnCl(4), and Et(3)SiClO(4) in the former reaction while TiCl(4) gives the highest selectivity for the less sterically demanding products in the latter case. These results are interpreted in terms of alternative reaction mechanisms. The reaction of less bulky ketene silyl acetals are initiated by electron transfer from these compounds to a Lewis acid. On the other hand, bulkier ketene silyl acetals undergo a ubiquitous nucleophilic reaction. Such a mechanistic change is discussed based on a variety of experimental results as well as the semiempirical PM3 MO calculations.     

Sphericity governs both stereochemistry in a molecule and stereoisomerism among molecules

The concept of sphericity and relevant fundamental concepts that we have proposed have produced a systematized format for comprehending stereochemical phenomena. Permutability of ligands in conventional approaches is discussed from a stereochemical point of view. After the introduction of orbits governed by coset representations, the concepts of subduction and sphericity are proposed to characterize desymmetrization processes, with a tetrahedral skeleton as an example. The stereochemistry and stereoisomerism of the resulting promolecules (molecules formulated abstractly) are discussed in terms of the concept of sphericity as a common mathematical and logical framework. Thus, these promolecules are characterized by point group and permutation group symmetry. Prochirality, stereogenicity, prostereogenicity, and relevant topics are described in terms of the concept of sphericity.     

Stereoselective synthesis of c3-c12 dihydropyran portion of antitumor laulimalide using copper-catalyzed oxonium ylide formation-[2,3] shift

Copper-catalyzed oxonium ylide formation-[2,3] shift of (5S,7R)-5-allyloxy-1-diazo-8-(p-methoxybenzyloxy)-7-methyl-2-octanone (3) proceeded in tetrahydrofuran-dichloromethane (4 : 1) under reflux with an excellent stereoselectivity (97 : 3) to give (2R,6S)-2-allyl-6-[(2R)-3-(p-methoxybenzyloxy)-2-methylpropyl]-3-dihydropyranone (2) as a major isomer in 82% yield. The resultant pyranone (2) was converted to the key intermediate (1) of the Mulzer's laulimalide synthesis and its derivatives (14, 15).     

Selective and sensitive fluorometric determinations of cobalt(II) and hydrogen peroxide with fluorescein-hydrazide

Fluorophotometric determinations of cobalt(II) and hydrogen peroxide were investigated by using the fluorescence reaction between fluorescein-hydrazide (fl-NHNH(2)), and/or hydrogen peroxide, cobalt(II), respectively. The calibration graphs were liner in the range of 0-6.0 ng cobalt(II) and 0-1000 ng hydrogen peroxide per 10 ml at an emission wavelength (E(m)) of 530 nm with an exicitation wavelength (E(x)) of 508 nm, respectively. These proposed methods were selective and simple, and the effect of foreign ions was negligible in comparison with conventional reported methods such as nitroso R,4-(2-pyridylazo)resorcinol(PAR), alizarin, pyridine-2-aldehyde-2-pyridinehydrazone, stilbazo-cobalt(II), etc.     

Highly sensitive spectrophotometric determination of osmium(VIII) with pyrogallolphthalein and hydrogen peroxide in the presence of Brij 35

Summary A highly sensitive determination of osmium(VIII) is based on the decolouring reaction with pyrogallolphthalein (gallein) and hydrogen peroxide in the presence of Brij 35. Beer's law was obeyed in the range of 0–0.5 ng of osmium(VIII) per 10 ml and the apparent decomposed absorption coefficient was 2.5×10⁹ l mol^–1 cm^–1 at 535 nm.Application of xanthene derivatives in analytical chemistry. Part XCIII. Part XCII see ref. [1]     

Synthesis and calcium antagonistic activity of (+)-(R)- and (-)-(S)-3-acetyl-2-[5-methoxy-2-[4-[N-methyl-N-(3,4,5- trimethoxyphenethyl)amino]butoxy]phenyl]benzothiazoline hydrochloride

SA2572 ((+)-1), 3-acetyl-2-[5-methoxy-2-[4-[N-methyl-N-(3,4,5-trimethoxyphenethyl) amino] butoxy]phenyl]-benzothiazoline hydrochloride is a newly synthesized Ca2+ antagonist having a inhibitory effect on the fast Na+ inward channel. In order to clarify the absolute configurations and the pharmacological properties of both enantiomers, compounds ((+)-1 and (-)-1) were synthesized. The configurations of these compounds were assigned on the basis of an X-ray crystallographic analysis of synthetic precursor (5). The in vitro Ca2+ channel blocking activities of (+)-1 and (-)-1 were evaluated in terms of the inhibitory activities on depolarization-induced contraction of guinea pig taenia cecum and rabbit aorta. The in vivo efficacy of the enantiomers was evaluated with their hypotensive effects in spontaneously hypertensive rats. Compound (-)-1 showed more potent Ca2+ antagonistic activities on guinea pig taenia cecum and rabbit aorta and the hypotensive effect than those activities of (+)-1. In the electrophysiological study of Langendorff perfused rabbit hearts, compound (+)-1 showed more potent inhibitory effect on the fast Na+ inward channel than that of compound (-)-1, and an approximately equal potent inhibitory effect on the slow Ca2+ inward channel as compared with compound (-)-1. Stereoselectivity of the pharmacological activity was found.     

Studies on the mechanism of 1,2-dihydropyrazin-2-one ring formation from dipeptidyl chloromethyl ketone and its chemical properties: immediate deamination during catalytic hydrogenation

1,2-Dihydropyrazin-2-one derivatives, which have two aminoalkyl groups at the positions 3 and 6, were found to be efficient tools for the construction of potent, selective and long-acting opioid mimetics. During the course of preparation, we found that the catalytic hydrogenation of 3,6-bis(benzyloxycarbonylaminomethyl)-5-methyl-1,2-dihydropyrazin-2-one to remove the benzyloxycarbonyl groups resulted in a side reaction. By MS and NMR studies and by preparation of additional 1,2-dihydropyrazin-2-one derivatives, the structure of the by-product was identified as 3-aminomethyl-5,6-dimethyl-1,2-dihydropyrazin-2-one. Preparation of additional compounds substituted with deuterium provided us with sufficient information to confirm the structure of the product and to support a cyclization mechanism in its formation.