Practical thiol surrogates and protective groups for arylthiols for Suzuki-Miyaura conditions

We have developed practical thiol surrogates and arylthiol protective groups for the Suzuki-Miyaura reaction. 2-Ethylhexyl-3-mercaptopropionate and 4-(2'-mercaptoethyl)pyridine were shown to be not only good thiol surrogates but also good protective groups for thiol. We have demonstrated toleration of these protective groups under aqueous Suzuki-Miyaura conditions.     

Preparation of CF3-containing 1,3-di- and 1,1,3-trisubstituted allenes

Novel synthetic pathway to access trifluoromethylated allenes with 1,3-di- as well as 1,1,3-trisubstitution patterns was developed from a variety of 4,4,4-trifluorobut-2-yn-1-ols which were then transformed into the corresponding vinylic iodides in highly regio- and stereospecific manners, and zinc-mediated beta-elimination after trifluoroacetylation of the hydroxyl group eventually realized the formation of the target molecules in good to excellent overall yields in facile and short steps.     

Raman spectroscopic study on the hydration structures of tetraethylammonium cation in water

Conformational changes of tetraethylammonium ion (Et4N+) in aqueous solution have been studied by Raman spectroscopy as functions of pressure and concentration. The difference in the partial molar volume (Delta V(tg x tg-->tt x tt)) between the trans-gauche x trans-gauche (tg x tg) and trans-trans x trans-trans (tt x tt) conformers of Et4N+ ion has been calculated from the pressure dependence of the relative Raman intensity ratio between the conformers. We discuss about the Delta V(tg x tg-->tt x tt) with two contributions from the molecular and hydration volumes. Delta V(tg x tg-->tt x tt) is found to be negative, and this is mainly due to the large molecular volume contribution. The value of Delta V(tg x tg-->tt x tt) becomes smaller with increasing R probably due to the hydration volume contribution. In view of the pressure and concentration dependences, the water molecules around Et4N+ ions at R = 19 (R= moles of water/moles of salt) mainly form the hydrophobic hydration. The hydrophobic hydration may prefer the tt x tt conformer to the tg x tg conformer. On the other hand, the hydration structure at R = 4 no longer forms the hydrophobic hydration and changes to another type of hydration, where the medium H-bond component is the dominant species. The increase of the ion-ion interactions with decreasing R induces large fractions of the tg x tg conformer.     

alpha-CD/crown-appended diazophenol for selective sensing of amines

[reaction: see text] Azophenol dyes having the permethylated cyclodextrin and/or crown moieties have been synthesized. Compound 1 provides critical information on discriminating 1-3 degrees amines with unique color changes. Addition of 1 degrees and 2 degrees amines to 1 shifts the absorbance maximum of 1 from 380 to approximately 580 and approximately 530 nm, respectively, but no change is observed with 3 degrees amines. The high selectivity of 1 is mainly due to H-bonding between the ammonium H atoms of the amine and oxygen atoms of the crown-6.     

Verticilide: elucidation of absolute configuration and total synthesis

Verticilide (1) is a 24-membered cyclic depsipeptide isolated from the culture broth of Verticillium sp. FKI-1033. It inhibits ryanodine binding to ryanodine receptor (RyR) and has insecticidal activity. The stereochemistry of 2-hydroxyheptanoic acid in verticilide was elucidated by chiral HPLC analysis of the degradation product 6 and synthetic (+) and (-)-6. We also describe the practical total synthesis of verticilide. [reaction: see text].     

Switching behavior of superconducting current injected from quasi-one-dimensional leads into mesoscopic samples

We have investigated the distribution of external current injected from superconducting leads into mesoscopic samples using time dependent Ginzburg-Landau theory. In particular, we have taken account of the current and field variation in the thickness direction. We have performed numerical simulations for the sample composed of two rectangular solids connected by two bridges. We have observed “switching” like behavior in the current distribution at the bridges, which corresponds to the change between vortex penetration and expulsion. This switching like behavior, as well as the magnitude of the currents, depends on the sample thickness in the direction of the external field.     

Experimental and modeling studies of grain size and moisture content effects on radon emanation

Some models have already been developed to explain the effect of moisture content on the radon emanation fraction of soil. For this purpose, “microscopic” soil models, which are easy to deal with mathematically but cannot take grain size into consideration, have been designed. These previous models consist basically of two opposite grain surfaces and pores between the grains. In the present study, in order to study the effect of not only moisture content but also grain size, we present a simple modeling approach based on two “macroscopic” soil models: (1) a single-grain model and (2) a multiple-grain model. The latter model represents a configuration of spherical grains packed in a simple cubic structure. Based on these soil models and general assumptions, the radon emanation fraction was calculated as a function of grain size or moisture content by Monte Carlo simulation. The results for the multiple-grain model show that the radon emanation fraction is markedly increased with grain sizes ranging from 10 to 100 μm and reaches a constant value of 50% when moisture content is 0% and the radium is uniformly distributed on the grain surface. Moreover, a drastic increase is seen at smaller grain sizes with increasing moisture content. From these results, we concluded that the calculation of radon emanation depends greatly on the pore size between a Ra-bearing grain and a neighboring grain. The validity of the model was also evaluated by comparison to experimental data.