Iodine intermediates

The iodine radical combines to form 12, which undergoes further chemistry with I. The result of complex reactions with other iodine intermediates provides the net capture of an iodine radical with the aryl radical to give product. 

The oxidation of carbonyl compounds can be achieved with hypervalent iodine reagents quite easily. A general feature of these reactions is the electrophilic attack of the hypervalent iodine reagent at the a-carbon atom of a carbonyl group and a review on this chemistry has been published recently [6]. This leads to hypervalent iodine intermediates of type 55. These phenyliodinated intermediates are quite unstable and a variety of subsequent reactions are possible. Intermediates 55, Scheme 24, can be considered as umpoled substrates regarding the reactivity of the a-position of the initial carbonyl compounds. Major processes are the substitution by a nucleophile (see Sect. 3.5.1 Functionalization in the a-Position) or the introduction of a carbon-carbon double bond (see Sect. 3.5.2 Introduction of an a,/ -Unsaturation). 

The products 58 of this reaction are of high interest as they can be used in a variety of subsequent reactions, Scheme 26. They can be used in next condensation reactions [120,121], which sometimes can be carried out as one-pot procedures [122]. Some examples are shown in Scheme 27. The combination of a-tosylation and reaction with amidines generates different substituted lH-imi-dazoles 60 [123]. Also polymer bound sulfonic acids can be used to trap the hypervalent iodine intermediates and to transfer subsequent steps to solid-phase synthesis [124]. Products of type 61 can be reacted with a variety of different bisnucleophiles to generate polycyclic compounds 62. 

The observations on these exchange reactions are in accord with the properties of the intermediates X2OH" postulated for halogen hydrolysis (section 6.1.7). Note that spectroscopic detection of the iodine intermediate has been claimed " . 

A related system involving also tricoordinate iodine intermediates is the reaction of trimethylsilyl phenylacetylene with aryl or alkyliodine difluorides which gave coupling products. Although no yields were reported, the relative ratios indicated that pentafluorophenyliodine difluoride led to the diyne as the main product [(93) (94) = 3.25] whereas perfluoropropyliodine difluoride led to the preferential formation of l-perfluoropropyl-2-phenylacetylene, (94) R = C3F7.209... 

The mechanism for this reaction was discussed in Section 13.5. For simplicity, we wiU ignore the formation of an iodine intermediate in calculating the equilibrium concentrations here. 

The reactions of the /3-halogenovinyliodonium salts 24a,b with halide ions are quite slow, but proceed at 60°C to give a substitution product, (Z)-l,2-dihaloalkene 25, with complete retention of configuration (Scheme 22)." No inverted products were detected. As shown in Fig. 8 the rate of the reaction changes with halide concentration in the same way as for the /3-elimination. That is, the reaction must occur as an intramolecular process of the A -haloiodane intermediate as does the j8-elimination. Another characteristic of the reaction is the formation of the retained iodoalkene 26. The results are best accounted for by the ligand coupling mechanism within the hypervalent iodine intermediate The trends have been explained... 

The discussion about the mechanism of excessive iodine supplementation-induced apoptosis remains controversial, there are several viewpoints (1) molecular iodine (intermediate products of oxidation) induces apoptosis (Golstein and Dumont, 1996) (2) reactive oxygen species (ROS) induce apoptosis (Vitale et al., 2000) (3) Fas—FasL induce apoptosis (Tamura et al, 1998 Feldkamp et al., 1999) (4) inhibition of Bcl-2 expression and an increase in Bax expression induce apoptosis (Yang et al., 2000) and (5) blocking the cell cycle of GO/Gl and G2/M induces apoptosis (Smerdely et al, 1993). 

TPO is a hemoprotein enzyme tvith binding sites for both iodine and tyrosine. In model systems, TPO has no catalytic activity in the absence of H2O2. TPO degrades H2O2 in a catalase-like reaction releasing O2. Several iodination intermediates were postulated for this reaction, for instance TPO-bound iodinium (U) andTPO-bound hypoiodite (I ). 

Reactions of4-hydroxy-2-cyclobutenones 364 with (diacetoxyiodo)benzene in 1,2-dichioroethane at reflux afford 5-acetoxy-2(5//)-furanones 365 as rearranged products (Scheme 3.146) [466], The formation of these products is explained by ring cleavage in the hypervalent iodine intermediate 366 foiiowed by recycliza-tion of the resulting acyl cation 367 with the carbonyl oxygen (Scheme 3.146). In a similar procedure,... 

Treatment of alkyliodides with peracids in the presence of water results in oxidatively assisted hydrolysis and the formation of alcohols [661]. This reaction can be used as a synthetic method for the mild hydrolysis of iodides for example, iodide 642 undergoes facile stereoselective hydrolysis to the protected amino alcohol 643 under neutral conditions upon exposure to ten equivalents of buffered peroxytrifluoroacetic acid (Scheme 3.252) [670]. The oxidatively assisted hydrolysis of iodide 642 results in a complete inversion of configuration, which is consistent with the 5n2 mechanism of substimtion in the hypervalent iodine intermediate [670]. 

This apparently simple reaction comprises a complex homogeneous catalytic oscillatory process involving numerous iodine intermediates [4,5,7-9,25,27,29,30,32-92]. The global reaction (D) is the result of the reduction (R) of iodate to iodine and the oxidation (O) of iodine to iodate by the following complex reaction scheme ... 

The cyclic periodate ester breaks down spontaneously, as shown below, creating a pair of carbonyl groups and a pentavalent, pentacoordinate iodine intermediate ... 

The iodine intermediate, which may be viewed as a hydrated form of iodic acid, should then eliminate water to yield iodate (103 ). A water-catalyzed pathway is shown below ... 

In 2008, Kim and Chang reported on the catalytic aziridination of styrenes and other olefins by 2-pyridylsulfonamide and PhROAc), using copper complexes [86]. These reactions do not require preformed (arylsulfonylimino)iodobenzenes PhlNS02Ar. During investigations of the mechanism, a copper PhINS02Ar complex was detected by ESI-MS as a major species (Scheme 21). A chelated nitrenoid complex derived from an unusual hypervalent iodine intermediate (Scheme 22) was proposed, based on Hammett plot analysis, kinetics and computational studies. 

Meanwhile in the reactions with milder oxidation agents, e.g. Hg(II) or Cu(II) salts or iodine, intermediate oxidation states of the clusters are obtained. 

Padwa and coworkers realized the synthesis of 2,4-disubstituted pyrroles using rearrangements of 2-fiiranyl carbamates via 5-methoxy-3-pyrrolin-2-one intermediates. 2-Furanyl carbamate 593 was treated with iodine and sodium bicarbonate followed by methyl iodide and silver oxide to give the N-substituted 5-methoxy-3-pyrrolin-2-one 595 via the iodinated intermediate 594 (Scheme 173 20090L1233). Padwa employed this method to synthesize 5-methoxypyrrol-2-ones, which were then treated with alkyl hthiates to give tricycHc products (2009T6720). 

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