Arenes diacetoxyiodo benzene

Most known iodonium salts of this category have one phenyl and one aryl group. Various hypervalent iodine precursors can be used as effective electrophiles, notably the combination of (diacetoxyiodo)benzene with triflic acid. The reagent is formed in situ and is suitable for a range of activated to weakly deactivated arenes. The reactions proceed at room temperature and in some cases, e.g. with anisole, only the p-isomer was produced. Strongly deactivated arenes such as nitrobenzene did not react. 

Various unsymmetrically substituted diaryliodonium triflates 269 can be synthesized by the reaction of iodosylbenzene [380] or (diacetoxyiodo)arenes [381] with arenes in trifluoromethanesulfonic acid (Scheme 2.76). This simple procedure affords diaryliodonium triflates in relatively high yields, but it is limited to aromatic substrates that are not sensitive to strong acids. In a milder, more selective variation of this procedure (diacetoxyiodo)benzene is reacted with arylboronic acids in the presence of triflic acid at -30 °C to afford aryl(phenyl)iodonium triflates in 74-97% yields [377]. 

Bis(acyloxy)iodo]arenes are useful for the oxidation of organic derivatives of bismuth and antimony [543,544], Triarylbismuthanes 452 react with (diacetoxyiodo)benzene in dichloromethane under mild, neutral conditions to afford pentavalent triarylbismuth diacetates 453, which can be isolated in good yields (Scheme 3.179) [543], Triarylstibines 454 react with PhI(OAc)2 under similar conditions to afford triarylan-timony(V) diacetates 455 [544],... 

Several useful synthetic methodologies are based on the generation of the oxygen-centered radicals from carboxylic acids and the (diacetoxyiodo)benzene-iodine system [613-617]. In particular, a direct conversion of 2-substituted benzoic acids 566 into lactones 567 via oxidative cyclization induced by [bis(acyloxy)iodo]arene/iodine has been reported (Scheme 3.224) [613,614]. 

Various oxidations with [bis(acyloxy)iodo]arenes are also effectively catalyzed by transition metal salts and complexes [726]. (Diacetoxyiodo)benzene is occasionally used instead of iodosylbenzene as the terminal oxidant in biomimetic oxygenations catalyzed by metalloporphyrins and other transition metal complexes [727-729]. Primary and secondary alcohols can be selectively oxidized to the corresponding carbonyl compounds by PhI(OAc)2 in the presence of transition metal catalysts, such as RuCls [730-732], Ru(Pybox)(Pydic) complex [733], polymer-micelle incarcerated ruthenium catalysts [734], chiral-Mn(salen)-complexes [735,736], Mn(TPP)CN/Im catalytic system [737] and (salen)Cr(III) complexes [738]. The epox-idation of alkenes, such as stilbenes, indene and 1-methylcyclohexene, using (diacetoxyiodo)benzene in the presence of chiral binaphthyl ruthenium(III) catalysts (5 mol%) has also been reported however, the enantioselectivity of this reaction was low (4% ee) [739]. 

The reactivity pattern of recyclable hypervalent iodine reagents 65-67,69-71,73,74 and 76 is similar to the common iodobenzene-based reagents [34], For example, the recyclable (diacetoxyiodo)arenes 65,69,73 and 76 can be used instead of (diacetoxyiodo)benzene in the KBr or TEMPO-catalyzed oxidations of alcohols [74-78], while [hydroxy(tosyloxy)iodo]arenes 67, 71 and 74 are excellent reagents for tosyloxylation of ketones (Scheme 5.28) [76]. 

Charette and coworkers have developed tetraarylphosphonium (TAP)-supported (diacetoxyiodo)benzene 109 (Figure 5.5), which can be used as a recyclable reagent or a catalyst for the a-acetoxylation of ketones [101]. Similarly to the imidazolium-supported [bis(acyloxy)iodo]arene 99, the reduced form of the TAP-supported reagent 109 can be recovered from the reaction mixture by simple filtration after treatment with ether. 

Methyl ester of serine rac-1 under treatment with (diacetoxyiodo) benzene (BAIB) and iodine gives radical 2, which is oxidized to give acyliminium ion 3. This intermediate is then trapped with acetate to yield N,0-acetal 4. The acyliminium ion 3 can regenerate from the acetal and react with vinyl arenes to produce the intermediate 5. In the final step, an intramolecular cyclization furnishes the 6-aryl-5,6-dihydro-4H-l,3-oxazine 6, with the ds isomer rac-6a as the major product (Scheme 5.3) [8]. In a similar domino process, aminosugars provide substituted oxazines, which are analogs of C-nudeosides [8]. 

Arene Amination. Alternative methods for the A-arylation of N-H-containing heterocycles that proceed directly with arenes (i.e., where aryl halides are not required) have emerged in the literature. In a recently reported procedure, a succinimide derivative was iV-arylated using palladium acetate as the catalyst, tri-ferf-butylphosphine as the ligand, and (diacetoxyiodo)benzene as a stoichiometric oxidant. This reaction allows the formation of ster-ically controlled products with monosubstituted arenes, yielding mainly meta- and / ara-arylated products and di- and trisubsti-tuted arenes, mostly providing the products of arylation at the meta-position (eq 15). ... 

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