Aryl Perfluoroalkyl Iodonium Salts

Alkyl and aryl thiols afforded with perfluoroalkyl iodonium salts in the presence of pyridine the corresponding sulphides in good to excellent yields [25], Several sulphides and sulphoxides upon reaction with trifluoroethyl phenyliodonium triflate were converted into 2,2,2-trifluoroethyl sulphonium salts [26]. 

Apart from the above two major general reaction pathways, there are some further possibilities for instance, [bis(trifluoroacetoxy)iodo]benzene reacts as an ambident electrophile and is attacked by hard nucleophiles at its carbonyl carbon, whereas iodylarenes may react similarly from carbon rather than iodine. Alkynyl iodonium salts are actually tetraphilic electrophiles, whereas iodosylbenzene reacts also as a nucleophile from oxygen. Diaryl iodonium salts serve as arylating reagents, mostly homolytically other iodonium salts transfer groups such as perfluoroalkyl, vinyl, alkynyl or cyano to several nucleophiles in various ways. 

Fluoroalkyl(aryl)iodonium salts are the most stable and practically important class of alkyl(aryl)iodonium derivatives. The application of such salts as electrophilic fiuoroalkylating reagents was reviewed in 1996 by Umemoto [1017]. Perfluoroalkyl(phenyl)iodonium trifiates (FITS reagents) 764 are efficient perfluoroalky-lating reagents toward various nucleophiUe substrates, sueh as arenes, carbanions, alkynes, alkenes, carbonyl compounds, amines, phosphines and sulfides [1017]. Scheme 3.300 shows several representative examples of electrophilic perfluoroalkylations using FITS reagents. 

Interestingly, the most basic of the iodonium reagents, aryl trifluoromethyl iodo-nium salts, are still unknown. They cannot be prepared by the methods outlined in Scheme 2.144. The presumed reason for this unexpected fact is the low stability of the carbon-iodine bond of their potential synthetic precursors CF3IF2 or CF3IO, compared with their analogs with two or more carbon atoms in the perfluoroalkyl chain [18]. 

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