Onium salt derived from

Among a series of trifluoromethyl dibenzoheterocyclic onium salts derived from chalcogens, a small number of tellurium compounds have been prepared. As electrophilic trifluoromethylating agents, the tellurium compounds appeared as the least reactive. With a very reactive carbanion, the unsubstituted dibenzotellurophenium salt (81) gave only 9% of the trifluoromethylated product. With the p-diketone enolate, (81) did not react. However, the 3,7-dinitrotellurophenium salt (82) showed a relative activity similar to that of the unsubstituted selenium compound (47). 1... 

Peptide synthesis. Based on analogy with use of onium salts derived from DMSO, Kenner and co-workers9 developed a useful new method of peptide synthesis. Tosic anhydride10 is allowed to react for 15 min. with excess hexa-methylphosphoric triamide to form the ditosylate (1). The solution is then cooled... 

The recent results reported by Cram are extremely important because his catalysts are chiral crown ethers, and represent one of the first attempts to develop novel structures without the inherent disadvantages of the ammonium salts described above. Such crowns yield products from Michael additions of 3-ketoesters to methyl vinyl ketone with optical purities up to 99%. A series of novel chiral onium salts derived from methionine have also been reported by Colonna and his coworkers. Although so far these have displayed no asymmetric induction in their reactions, they are important as an imaginative new series of catalysts. 

Also of considerable encouragement were the results reported in the Darzens reaction some time ago . Carbonyl compounds when reacted with chloromethyl-p-tolyl sulphone or with chlorophenyl-acetonitrile in the presence of aqueous sodium hydroxide and chiral onium salts derived from [I] [reaction 7 and 8] yielded product epoxides with up to 2.5% enantiomeric excesses. More importantly. 

Though these alkaloids are not truly composed of two identical monomeric units, they are popularly named dimers or dimeric alkaloids. We prefer to avoid this incorrect nomenclature and would like to encourage the use of the more adequate binary terminology. In another consideration of nomenclature, we describe quaternary salts derived from an imine functionality as imonium salts, in accord with the descriptor for other onium salts (ammonium, oxonium, etc.), rather than by the frequently used iminium terminology. This nomenclature was suggested earlier (/). 

Davis recently reported triflimide salts derived from classical Girard s reagents which are hydrazine derived onium salts [29],... 

Spelling of amonium, imonium, and iminium indicates derivation from amine and imine onium salts. 

The most common ligands are those derived from imidazole and benzimidazol (Scheme 54), followed by the (benz)thiazols. The free Wanzlick-Arduengo carbenes can be isolated and employed for the synthesis of the complexes, but often it is more convenient to prepare the carbenes in situ from the dimers or the corresponding onium salts, or to use carbene-transfer reactions.256-259... 

Abstract This chapter focuses on well-defined metal complexes that serve as homogeneous catalysts for the production of polycarbonates from epoxides or oxetanes and carbon dioxide. Emphasis is placed on the use of salen metal complexes, mainly derived from the transition metals chromium and cobalt, in the presence of onium salts as catalysts for the coupling of carbon dioxide with these cyclic ethers. Special considerations are given to the mechanistic pathways involved in these processes for the production of these important polymeric materials. 

Under the same reaction conditions, catalytic activity is greater for cryptands than crown ethers or quaternary onium salts (111, 113). A series of polymer cryptands derived from the vinyl-containing monomer 16 have been discussed and could well find useful application (114). 

Ambient temperature molten salt can be obtained by several methods. One effective way to obtain a room-temperature molten salt is by the introduction of polyether chains to ions. The term polyether/salt hybrid is used in this chapter as a common name for polyether oligomers having anionic or cationic charge(s) on the chain (Figure 22.1). Polyethers, such as poly-(ethylene oxide) (PEO), are known as representative ion conductive polymers [1]. Polyether/salt hybrids have been studied as a kind of room-temperature molten salt apart from the development of onium-type ionic liquids [2]. The preparation of ionic liquids consisting of metal ions has been one of the important goals in this research field. Polyether/salt hybrid derivatives give one such solution for this task. 

All other TSOS are generally obtained from halogen, alcohol or amine derived onium salts. However, purifications of salt mixtures are often tricky and preparation methods often need to be carefully optimized. In some cases, when compatible with other functional group, quatemarisation can be performed at a later stage in the process. 

Apart from ammonium derived hydroxide, few onium salts have been used as supported bases. However, an analog of Hunig s base was prepared and employed as a catalyst in Knoevenagel condensations [68], Increase in the linker length was found critical to observe a good activity, as cation effect on amine basicity can be detrimental for short alkyl chains. Finally, using a biphasic liquid-liquid mixture, no significant decrease in activity has been noticed after five cycles (Fig. 25). 

Due to the attractivity of this method several groups have developed onium salt supported versions of classical reactions. For example, starting from hydroxyl derived imidazolium salts, formation of supported acrylates with acryloyl chloride followed by reaction with diene in refluxing toluene afforded Diels Alder adduct in good yields (>65%). After saponification, products are isolated without further purification [127], Alternatively, starting from carboxylic acid derived imidazolium salts, acyl chloride formation with thionyl chloride in acetonitrile, followed by reaction with 4-aminophenol led to supported N-arylamide. Williamson alkylation using NaOH as a base and subsequent cleavage from the onium salt support under acidic condition (HCI/I I2()/ AcOH) allowed for isolation of various alkoxy substituted anilines with >98% purity... 

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