Phenyliodonium salts

E-(P-Alkylvinyl)phenyliodonium salts react with tetra-n-butylammonium halides to yield the correspondingly substituted Z-haloethenes (80-100% for chloro-, bromo- and iodo-derivatives) [41], In contrast, in the corresponding reaction with Z-(2-benzenesulphonyl-ethenyl)phenyliodonium salts, nucleophilic substitution occurs with retention of configuration to yield the Z-2-benzenesulphonyl-l-haloethenes [42], The ammonium fluorides fail to yield the fluoroethenes, but produce the ethynes by simple elimination [41]. Where carboxylic acids have low solubility in organic solvents, their conversion into the acid chlorides is frequently difficult. Phase-transfer catalysis not only allows the conversion to be effected rapidly, it also results in high yields of a wide range of acid chlorides [43]. 

The work of Ochiai s group on nucleophilic vinylic substitution of phenyliodonium salts (see previous section) has been extended to examining the behaviour of allenyl (aryl)iodine(III). Ratios of nucleophilic substitution to [3,3]-sigmatropic rearrangement for the collapse of allenyl(aryl)iodine(III), generated from the reactions of aryliodanes... 

The only compounds of this type are some phenyliodonium salts with a carbo-ranyl group, obtained from 9-o-, 9-m- and 2-p-iodocarboranes which were converted into (dichloroiodo) and then into [bis(trifluoroacetoxy)iodo]carboranes these were coupled with benzene in presence of acid [84]. 

Some phenyliodonium salts not belonging to the above types are of special interest because they have been used as reagents, e.g. PhI+CN TfO" [135]. Another interesting iodonium salt not yet fully explored is the a-phenyliodonio-diazo compound which has been obtained from ethyl diazoacetate and (diacetoxyio-do)benzene in presence of Me3SiOTf (Scheme 49) [147]. 

Phenyliodonium Salt-Mediated Reactions Leading to Diaryl Ether... 

Total Synthesis via Phenyliodonium Salt-Mediated Reactions. . . 239... 

Phenyliodonium salt-induced reactions are also applicable to total syntheses of several natural products having biaryl ether moieties and polycyclic nitrogen heterocycles. 

Irradiation of phenyliodonium salts lead to the formation of phenyl radicals. In the presence of C60 these radicals are efficiently trapped under formation of pheny-lated C6o derivatives, mainly the monoadduct. In reaction mixtures of C6o, phenyliodonium salts and spin traps like nitroso-tert-butane ( BuNO) or nitroso-durene (ND) no phenyl adducts with the spin traps could be observed after irradiation. This suggests that C6o is a more efficient scavenger for phenyl radicals than the spin traps [177], Other investigations yielded similar results, e.g., the photolysis of organomercury compounds in the presence of fullerenes leads to fullerene-derived radical adducts. These radical adducts can combine to form dimers that are thermally stable and accumulate in the samples [Eq. (7)] [178],... 

Diphenyliodonium chloride, bromide, and iodide Aldrich, Lancaster Perfluoroalkyl phenyliodonium salts TCI America... 

Because of the multitude and diversity of iodonium salts and zwitterions, some of which are labile or are prepared for specific purposes, their preparative methods are discussed in Chapter 8, for diaryl iodonium salts and related compounds, Chapter 9 for perfluoroalkyl, alkenyl and alkynyl phenyliodonium salts and Chapter 10 for zwitterionic iodonium compounds. In addition, the preparation of some lesser known reagents, including 2-iodosylbenzoic acid, is given in Chapter 12. 

In contrast to (diacetoxyiodo)benzene, [bis(trifluoroacetoxy)iodo]benzene, (BTI) reacts in aqueous solvents with both terminal and non-terminal alkynes affording eventually a-hydroxyketones and 1,2-diketones, respectively. The primary reaction of terminal alkynes leads to the formation of alkynyl phenyliodonium salts, which are not isolable under the experimental conditions but have been prepared by other routes (Section 9.1.3) these are hydrolysed in situ to a-hydroxymethyl ketones, through the intermediacy of their O-tri fluoroacetates, which sometimes may be isolated as by-products. 

The reaction was of general applicability not only internal but also terminal alkynes reacted in the same way, e.g. 1-hexyne was converted into hexanoic acid (58%) and 2-ethynylthiophene to 2-thienylacetic acid (54%). By contrast, heating terminal alkynes in chloroform with HTI afforded alkynyl or alkenyl phenyliodonium salts the former in refluxing methanol rearranged to methyl carboxylates [11],... 

Some bridgehead amines such as 4-iodo-l-cubylamine (58%) and 1-adamantyl-amine (85%) were also obtained in this way [47]. The direct formation of alkylammonium tosylates is advantageous because of the instability of some amines of this type. No special precautions, as with BTI, were needed with HTI which, however, did not work with some cyclic carboxamides also, malonamide did not undergo degradation but tosyloxylation, affording a-tosyloxymalonamide (81%) [48]. The reaction involved the intermediacy of TV-phenyliodonium salts (RCONHI + Ph TsO-), which were actually isolated from carboxamides and [methoxy(tosyloxy)iodo]benzene [49]. 

The phenyliodonium salt of carbostyril on reaction with phenol, in the absence of solvent, was converted into a phenolic derivative [57] ... 

Whereas oxygen nucleophiles gave poor yields of alkenylated products with alkenyl iodonium salts, the reactions with sulphur nucleophiles proceeded more efficiently, leading to unsaturated sulphides and sulphones. Thus, 4-t-butylcyclohexenyl phenyliodonium salts afforded with sodium thiophenoxide 4-t-butylcyclohexenyl phenyl sulphide (81%) [3] and with sodium phenylsulphinate the corresponding sulphone (29%) in the presence of 18-crown-6, the yield of the latter rose to 80% [45]. jS-Phenylsulphonylalkenyl iodonium salts with sodium phenylsulphinate at 0°C, without any catalyst, afforded Z-l,2-bis(phenylsulphonyl)alkenes, in high yield with retention of the stereochemistry [45] ... 

Phenyliodonium Salts with an Aliphatic Moiety Preparative Methods. Reactivity of Perfluoroalkyl Phenyliodonium Salts. Reactivity of Other Iodonium Salts. 

The reaction of the 3-phenyliodonium salt of quinolin-2,4-diol (28) with various nucleophilic reagents led to the ligand coupling products in good yields. (Scheme 5.3)... 

In the case of unsyimnetrical diaryliodonium salts (the anisyl, tolyl or nitrophenyl derivatives of phenyliodonium salts - or some thienyl aiyliodonium salts ), the product composition is always in favour of the ligand coupling product involving the less electron-rich arene group. A good yield of 3-methoxyindole (60%) was obtained in the reaction of phenyl 3-indolyliodonium chloride with methanol in the presence of boron trifluoride-etherate. ... 

Like perfluoroalkylation, electrophilic a,a-dihydroperfluoroalkylation can be efficiently performed by the use of the appropriate (a,a-dihydroperfluoroalkyl)phenyliodonium salts. A wide range of nucleophiles were alkylated under mild conditions. Most of the reactions can occur by a ligand coupling taking place on an intermediate trisubstituted iodane(UI) compound. This is the case of the reactions with carbanions, amines, alkoxides, phenoxides, thiolates and carboxylic acid ammonium salts. Dialkylation of aniline was also obtained by using two molar equivalents of the iodonium reagent.219,220 (Table 5.11)... 

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