Highlights of C (sp2)–H hydrogen isotope exchange reactions

The highlights of C (sp²)–H hydrogen isotope exchange (HIE) methods developed over the past 10 years are summarized in this review. Major developments include improved Ir(I) catalysts with greater functional group and solvent compatibility and the development of novel base metal catalysts for HIE. In addition, a number of novel Ru-based catalysts have been developed with promising activity. In the area of Pt- and Pd-catalysed exchange, in addition to new advances on heterogeneous Pt- and Pd-catalysed HIE by Sajiki and Shevchenko, a number of groups have reported on homogenous catalysts of Pt and Pd that show an interesting activity and selectivity.     

1-(Triethoxysilyl)buta-1,3-dienes—New Building Blocks for Stereoselective Synthesis of Unsymmetrical (E,E)-1,4-Disubstituted 1,3-dienes

A convenient methodology for the highly stereoselective synthesis of unsymmetrical (1E,3E)-1,4-disubstituted 1,3-dienes based on palladium-catalyzed Hiyama cross-coupling reaction of 1-(triethoxysilyl)-substituted buta-1,3-dienes with aryl iodides is reported.     

Synthesis of a high specific activity methyl sulfone tritium isotopologue of fevipiprant (NVP‐QAW039)

The synthesis of a triple tritiated isotopologue of the CRTh2 antagonist NVP‐QAW039 (fevipiprant) with a specific activity >3 TBq/mmol is described. Key to the high specific activity is the methylation of a bench‐stable dimeric disulfide precursor that is in situ reduced to the corresponding thiol monomer and methylated with [³H₃]MeONos having per se a high specific activity. The high specific activity of the tritiated active pharmaceutical ingredient obtained by a build‐up approach is discussed in the light of the specific activity usually to be expected if hydrogen tritium exchange methods were applied.     

A convenient method for palladium‐catalyzed reductive deuteration of organic substrates using deuterated hypophosphite in D2O

A convenient method for the deuteration of organic substrates using deuterated hypophosphite as the deuterium source was investigated. Transfer deuteration of organic substrates, such as aromatic halides, alkenes, alkynes, epoxides, and O‐benzyl derivatives, in the presence of palladium on carbon in deuterium oxide proceeded efficiently to give the corresponding deuterated products in excellent yields with high deuterium contents.     

Preparation of Palladium-Supported Periodic Mesoporous Organosilicas and their Use as Catalysts in the Suzuki Cross-Coupling Reaction

Three periodic mesoporous materials, i.e., two organosilicas with either ethylene or phenylene bridges and one silica, have been used as supports for Pd nanoparticles. All Pd-supported samples (1.0 wt%) were prepared by the incipient wetness method and subsequently reduced in an H₂ stream at 200 °C. Both hydrogen chemisorption and temperature programmed reduction experiments revealed significant differences depending on the support. Pd²⁺ species were more reducible on the mesoporous organosilicas than on their silica counterpart. Also, remarkable differences on the particle morphology were observed by transmission electron microscopy. All Pd-supported samples were active in the Suzuki cross-coupling reaction between bromobenzene and phenylboronic acid.     

Carrier‐effect on palladium‐catalyzed,nucleophilic 18F‐fluorination of aryl triflates

A recently published palladium‐catalyzed preparation of fluoroarenes starting from caesium fluoride attracted interest as a new alternative for radiofluorination. To test this method, a suitable protocol for the synthesis of 4‐[¹⁸F]fluorotoluene and 1‐[¹⁸F]fluoronaphthalene as model systems has been developed. The possibility to perform the reaction under no‐carrier‐added condition was of special interest. It was found out, however, that the reaction requires the presence of carrier, thus limiting the method to syntheses of radiotracers with low specific activity. Copyright © 2012 John Wiley & Sons, Ltd.     

Contact dermatitis to metals

Metals are in close contact with skin and mucous membranes on a repeated, if not constant, basis. Nickel and mercury, well-recognized causes of contact dermatitis; gold and palladium, recently gaining acceptance as patch test allergens on standard screening trays; and cobalt are reviewed in this article. Sensitization to nickel, the most frequently identified allergen on patch testing, is associated with ear piercing. Contact with this potential allergen is ubiquitous. Mercury may be encountered as organic mercury in thimerosal, used as an antiseptic and a preservative in topical medications and vaccines, and metallic mercury found in dental amalgam and thermometers. Both forms may cause contact dermatitis. Gold, recognized as a frequent sensitizer, has been implicated in some cases of eyelid, patchy diffuse and oral lichenoid dermatitis. Cobalt allergy, found frequently in patients who are nickel allergic, also has been associated with ear piercing. Palladium sensitivity is often associated with nickel allergy. However, the incidence of clinical relevance is yet to be established.