Flexible metathesis-based approaches to highly functionalised furans and pyrroles

A range of differentially functionalised furans and pyrroles have been synthesised in short order by the judicious use of a ring-closing metathesis/aromatisation strategy. Two contrasting approaches are described exploiting a palladium-catalysed union of allylic alcohols and sulfonamides in one case, and a titanium mediated methylenation of homoallylic esters in another. A number of groups that are difficult to install via traditional methods were incorporated successfully.     

What happened before the last five strong earthquakes in Greece: Facts and open questions

During the period October 2005 - January 2006, five strong earthquakes occurred in Greece as follows: three magnitude 6.0 consecutive earthquakes with almost the same epicenter in the Aegean Sea close to the western coast of Turkey, one magnitude 6.1 in western Greece and one magnitude 6.9 in southern Greece. In March 2005 and September 2005, intense anomalous geoelectric changes were observed at two different stations respectively: one in the Aegean Sea and the other in western Greece. These changes were immediately reported to international journals well in advance of earthquake occurrences. Natural time analysis of seismicity subsequent to the September changes around the epicenter of the last 6.9 earthquake is made. The results indicate that the occurrence time of the 6.9 earthquake can be specified with a narrow range around two days.     

A geometric interpretation of frictional contact mechanics

The work-conjugacy of pressures and tangential tractions with so-called “gap”and “stick” constraints is deduced in order to delineate a rigid-plastic model of a frictional interface. This is accomplished by pursuing a differential-geometric view of the two surfaces that comprise the frictional interface. Given that contact is described in the current configuration, Lie derivatives are shown to be the natural means of establishing the work-conjugacy between tractions and constraints.     

Reaction of 3,4,4,5-tetrachloro-4H-1,2,6-thiadiazine with benzyltriethylammonium chloride

3,4,4,5-Tetrachloro-4H-1,2,6-thiadiazine was reacted with BnEt₃NCl (10?mol%) to give perchloro-9-thia-1,5,8,10-tetraazaspiro[5.5]undeca-1,4,7,10-tetraene (up to 18% yield), 4,5,6-trichloropyrimidine-2-carbonitrile (up to 44% yield) and four minor side products: 2,7-dichlorothiazolo[5,4-d]pyrimidine-5-carbonitrile, 2-(4-chloro-6H-thiazolo[5,4-c][1,2,6]thia-diazin-6-ylidene)malononitrile, 4,8-dichloropyrrolo[2′,1′:2,3]imidazo[4,5-c][1,2,6]thiadiazine-6,7-dicarbonitrile and 4,7-dichloro-[1,2,6]thiadiazino[3,4-b]thiazolo[5,4-e][1,4]diazepin-9(10H)-one. Single crystal X-ray studies support the structures of the minor products. Tentative rationale for the formation of these minor products and the synthesis of 8-bromo-4-chloropyrrolo[2′,1′:2,3]imidazo[4,5-c][1,2,6]thiadiazine-6,7-dicarbonitrile are presented.     

XeNA: An automated ‘open-source’ Xe hyperpolarizer for clinical use

Here we provide a full report on the construction, components, and capabilities of our consortium’s “open-source” large-scale (~ 1 L/h) ¹²⁹Xe hyperpolarizer for clinical, pre-clinical, and materials NMR/MRI (Nikolaou et al., Proc. Natl. Acad. Sci. USA, 110, 14150 (2013)). The ‘hyperpolarizer’ is automated and built mostly of off-the-shelf components; moreover, it is designed to be cost-effective and installed in both research laboratories and clinical settings with materials costing less than $125,000. The device runs in the xenon-rich regime (up to 1800 Torr Xe in 0.5 L) in either stopped-flow or single-batch mode—making cryo-collection of the hyperpolarized gas unnecessary for many applications. In-cell ¹²⁹Xe nuclear spin polarization values of ~ 30%–90% have been measured for Xe loadings of ~ 300–1600 Torr. Typical ¹²⁹Xe polarization build-up and T₁ relaxation time constants were ~ 8.5 min and ~ 1.9 h respectively under our spin-exchange optical pumping conditions; such ratios, combined with near-unity Rb electron spin polarizations enabled by the high resonant laser power (up to ~ 200 W), permit such high P_Xe values to be achieved despite the high in-cell Xe densities. Importantly, most of the polarization is maintained during efficient HP gas transfer to other containers, and ultra-long ¹²⁹Xe relaxation times (up to nearly 6 h) were observed in Tedlar bags following transport to a clinical 3 T scanner for MR spectroscopy and imaging as a prelude to in vivo experiments. The device has received FDA IND approval for a clinical study of chronic obstructive pulmonary disease subjects. The primary focus of this paper is on the technical/engineering development of the polarizer, with the explicit goals of facilitating the adaptation of design features and operative modes into other laboratories, and of spurring the further advancement of HP-gas MR applications in biomedicine.     

A study on the effect of electronic engine speed regulator on agricultural tractor ride vibration behavior

In this study, the effect of electronic speed adjustment on tractor ride vibration levels is examined. With normal pedal operation the engine rotational speed drops with an increasing load. The electronic regulator provides a constant speed mode of operation independent of the load. Vibration levels were measured under different operating conditions and surfaces. As a first series of tests, the tractor was driven on a conglomerate bituminous track at speeds of 20, 25 and 28 km/h. Vibration was measured upon the surface of the operator seat simultaneously in the x, y and z directions. The reference axis system was that defined by the ISO 2631-1 [1]. The weighted r.m.s. acceleration was found to be between 8% and 8.6% higher for the case where operation with electronic speed adjustment had been selected. Secondly, cultivating was chosen as the field task and the vibration was measured while the tractor was traversing a rough farm track at speeds of 6, 7.5 and 9 km/h. In this case, the vibration levels with automatic speed adjustment were between 4.3% and 8.6% lower than when driving with normal foot pedal operation. From the above results, we may infer that electronic speed regulation should not be used in transportation on asphalt country roads. On the contrary, it seems that electronic regulation has an advantage when used in typical field tasks such as cultivating.     

Synthesis of [(4-chloro-5H-1,2,3-dithiazol-5-ylidene)amino]azines

The reactions of 2-, 3- and 4-aminopyridines with 4,5-dichloro-1,2,3-dithiazolium chloride (Appel salt) 4 to give N-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)pyridin-X-amines 1a (X = 2), 1g (X = 3) and 1k (X = 4) were optimized with respect to base, temperature and reaction time. Based on these conditions a total of thirteen [(dithiazolylidene)amino]azines 1a-m were prepared and fully characterized.     

Preparation of 2-Picolylarsonic Acid and its Reductive Cleavage by Ascorbic Acid/Iodine and by Thiophenol

Contrary to dialkylaminoethyl halides, 2-picolyl chloride reacts with alkaline arsenite to give nearly quantitative yields 2-picolylarsonic acid. This acid is decomposed by ascorbic acid in the presence of catalytic amounts of iodine to 2-picoline and arsenious acid, most likely by hydride transfer from the ascorbic acid. Thiophenol decomposes this arsonic acid very quickly to 2-picoline, diphenyl disulfide and triphenyl trithioarsenite. In this case a proton from the thiophenol is transferred to the incipient 2-picolyl carbanion.     

Racemic 2,3,4-Triacyloxybutylarsonic Acids: A New Class of Arsonolipids with Three Acyl Chains

Abstract

A new class of arsonolipids, racemic 2,3,4-triacyloxybutylarsonic acids, having three fatty acyl chains per molecule have been prepared starting from the key compound 2,3,4-trihydroxybutylarsonic acid after investigating various acylating conditions in order to minimize the interference from As(III). Yields as high as 75% were obtained by adding neat acyl chloride dropwise to a cold (0°C) solution of diphenyl 2,3,4-trihydroxybutyldithioarsonite, pyridine, and catalytic amounts of 4-dimethylaminopyridine in dichloromethane. The new arsonolipids are glasses or soft solids, whose spectral properties are discussed.     

Three-step synthesis of ethyl canthinone-3-carboxylates from ethyl 4-bromo-6-methoxy-1,5-naphthyridine-3-carboxylate via a Pd-catalyzed Suzuki-Miyaura coupling and a Cu-catalyzed amidation reaction

Ethyl canthin-6-one-1-carboxylate (1b) and nine analogues 1c-k were prepared from readily prepared ethyl 4-bromo-6-methoxy-1,5-naphthyridine-3-carboxylate (2b) via a three-step non-classical approach that focused on construction of the central pyrrole (ring B) using Pd-catalyzed Suzuki-Miyaura coupling followed by Cu-catalyzed C-N coupling. Furthermore, treatment of the ethyl canthinone-1-carboxylate 1b with NaOH in DCM/MeOH (9:1) gave the canthin-6-one-1-carboxylic acid (6) in high yield. All compounds are fully characterized.