Iodine III Compounds

Radical reactions of Hoffmann-Loffler-Freytag type with participation of iodine(III) compounds leading to five-member N-heterocycles 97YGK90. 

Since the completion of the manuscript the following work on the synthesis and isolation of new Amaryllicaceae alkaloids (cf. following page) was reported. Large scale syntheses [180,181] of ( )-narwedine (291) and (-)-galanthamine (295) have been reported. Rita and co-workers have described [182] the use of hypervalent iodine(III) compounds to achieve die total syntheses of ( )-sanguinine (535 R2=Me), ( )-galanthamine (295), ( )-narwedine (291) and ( )-lycoramine (300). 

The purpose of present review is to summarize the application of different classes of iodine(III) compounds in carbon-carbon bond forming reactions. The first two sections of the review (Sects. 2 and 3) discuss the oxidative transformations induced by [bis(acyloxy)iodo] arenes, while Sects. 4 through 9 summarize the reactions of iodonium salts and ylides. A number of previous reviews and books on the chemistry of polyvalent iodine discuss the C-C bond forming reactions [1 -10]. Most notable is the 1990 review by Moriarty and Vaid devoted to carbon-carbon bond formation via hypervalent iodine oxidation [1]. In particular, this review covers earlier literature on cationic carbocyclizations, allyla-tion of aromatic compounds, coupling of /1-dicarbonyl compounds, and some other reactions of hypervalent iodine reagents. In the present review the emphasis is placed on the post 1990s literature. 

Alkenyl(phenyl)iodine(III) compounds can also serve as starting materials in rearrangements. Allenyl(aryl)iodine(III) compounds of type 86 can be synthesized from (diacetoxyiodo) derivatives 85 and propargylsilanes [145]. It depends on the leaving group ability of the aromatic substituent on iodine in 86 as to whether the reaction proceeds via nucleophilic substitution to compounds of type 87 or by an iodonio-Claisen rearrangement to compounds 88, Scheme 37 [146,147]. The easy access to propynyl compounds 87 has been shown [148] and solvent effects in these reactions have been investigated as well [149,150]. 

Review. Moriarty and Koser3 have reviewed this hypervalent iodine(III) compound. It is particularly useful for vie, ciy-ditosyloxylation of alkenes, a-tosylation of ketones, and conversion of primary amides to amines. 

Since A3-iodanes figure prominently in the synthesis of alkynyliodonium salts, a brief description of this class of iodine(III) compounds is presented here. 

Several iodine nitrates in the oxidation state +III are known I(0N02)3 and CF3l(0N02)2- The other halogens do not form binary nitrates in the oxidation state +III. Iodine (III) nitrates are available by substitution of iodine(III)compounds... 

The iodine(iii) compound has also been reported by Seppelt he obtained it by the action of ClOTeFs on ICI3. The product is stable to 180°C but very readily hydrolysed. The same worker has demonstrated that Br(OSeF6)3 possesses appreciable acceptor properties (its F n.m.r. spectrum is indicative of rapid ligand exchange) and has prepared Rb+Br(OSeF5). ... 

Silva and Lopes analyzed solutions of iodobenzene dicarboxylates in acetonitrile, acetic acid, aqueous methanol and anhydrous methanol by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS) [196]. The major species found in the solutions of PhI(OAc)2 in acetonitrile, acetic acid and aqueous methanol were [PhI(OAc)2Na]+, [PhI(OAc)2K]+, [Phl]+, [PhIOAc]+, [PhIOH]+, [PhI02Ac]+, [PhI02H]+ and the dimer [Ph2l202Ac]+. On the other hand, the anhydrous methanol solutions showed [PhIOMe]+ as the most abundant species. In contrast to the data obtained for PhI(OAc)2, the ESI-MS spectral data of PhI(02CCF3)2 in acetonitrile suggests that the main species in solutions is iodosylbenzene [196]. A similar ESI-MS and ESI-MS/MS study of solutions of [hydroxy(tosyloxy)iodo]benzene has been performed under different conditions and, based on these data, mechanisms were proposed for the disproportionation of the iodine(III) compounds into iodine(V) and iodine(I) species [197]. 

The known classes of iodine(III) compounds without carbon ligands are represented by the iodine(III) halides and by the derivatives of unstable iodine(III) oxide, I2O3, of types OIOR or I(OR)3. Table 2.1 summarizes the known inorganic iodine(III) compounds. 

Organic iodine(III) dichlorides, RICI2, are usually prepared by direct chlorination of organic iodides, or, less commonly, by ligand exchange in other iodine(III) compounds. Table 2.3 summarizes the preparation methods for organic iodine(III) dichlorides. 

Organic iodosyl compounds usually have a polymeric structure, (RIO) , with a typical, for X -iodanes, T-shaped geometry at the iodine atom no structural evidence supporting the existence of an 1=0 double bond has been reported. Most known iodosyl compounds have low thermal stability and some are explosive upon heating. Iodosyl compounds can be prepared by direct oxidation of organic iodides, or, more commonly, by basic hydrolysis of other iodine(III) compounds. Table 2.4 summarizes the preparation methods for organic iodosyl compounds. 

Hypervalent iodine(III) compounds, such as [bis(trifluoroacetoxy)iodo]benzene, (diacetoxyiodo)benzene and [hydroxy(tosyloxy)iodo]benzene, are commonly used as reagents in various cationic cyclizations, rearrangements and fragmentations. Numerous examples of such reactions have been reported in the literature and summarized in the reviews dedicated to synthetic applications of hypervalent iodine compounds [4,7,10,11, 180, 191, 387]. 

Hypervalent iodine(III) compounds have found wide application for the oxidation of organic derivatives of nitrogen, sulfur, selenium, tellurium and other elements. Reactions of X -iodanes with organonitrogen compounds leading to the electron-deficient nitrenium intermediates and followed by cyclizations and rearrangements (e.g., Hofmann rearrangement) are discussed in Section 3.1.13. Several other examples of oxidations at a nitrogen center are shown below in Schemes 3.168-3.170. 

Addition of two nitrogen moieties to an alkene was initially reported within the historic diazidonation reaction. In 1986, Moriarty reported such a diazidonation using PhIO as the terminal oxidant in combination with NaNa and in AcOH as solvent, which allowed for facile diazidonation of several alkenes [58]. Unfoitu-nately, functional group tolerance was a major problem and, as the consequence of the underlying radical mechanism for the double bond oxidation, the corresponding diazide products were obtained as diastereomeric mixtures. More defined conditions to generate the hypervalent iodine(III) compound PhI(N3)2 were used by Magnus, which provided an advanced diazidonation protocol [59-62]. 

In stepwise reactions, an iodoarene is first oxidized to an iodine(III) compotmd under acidic conditions. After isolation, the iodine(III) compound is treated with an arene or an arylstannane, aryl boronic acid, or arylsilane to reach Ar2lX [4]. A subsequent anion exchange is sometimes required to obtain a diaryliodonium salt that can be easily isolated and applied in arylations without interference from the... 

Aldimines 17 of 2-aminophenol are oxidatively cyclized to 2-substituted benzoxazoles mediated by the hypervalent iodine(III) compound PhI(OAc)2 in CH3OH [288] ... 

Wirth and coworkers prepared iodoxolones 66, 68, 70, and 71 by the oxidation of (Z)-3-iodo acrylic acid derivatives 65, 67, and 69 using peracetic acid or other common oxidants (Scheme 5 2009OL3578). Structures of products 66 and 68 were established by X-ray analysis (2009OL3578). Bond angles and distances within the five-membered iodoxolone system are similar to the respective X-ray structural parameters of 1-hydroxybenziodoxole derivatives (see Section 3.2.2.2 1964NAT512, 2007ACE6529). lodoxolones 66, 68, 70, and 71 have stability and reactivity similar to the noncyclic hypervalent iodine(III) compounds (2009OL3578). 

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