Double Hypervalent iodine

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). 

Such additions of nucleophiles to non-activated double bonds mediated by hypervalent iodine compounds are also possible in other cases (Section 3.5). This umpolung of reactivity is due to the formation of an adduct with hypervalent iodine which renders this intermediate highly electrophilic. In this way 6-propionylflavo-nols gave 1,2-dimethoxy-adducts in methanol-perchloric acid [10] ... 

Reactions of alkenes with hypervalent iodine compounds lead mostly to vicinally functionalised alkanes. This is the case with PhI(OAc)2, PhIO, PhI(OH)OTs, PhI(OTf)0(TfO)IPh and other related reagents.230,231,233,239-247 poj. example, treatment of alkenes with PhI(OH)OTs, (HTIB), affords vie bis(tosyloxy)alkanes with a syn stereospecificity.239,241 n generally admitted that this reaction proceeds by the electrophilic attack of the hypervalent iodine species on the ethylenic double bond to afford a carbonium ion intermediate (140). This intermediate undergoes two consecutive Sn2 substitution reactions to eventually give the final products. (Scheme 5.17)... 

The aminohalogenation of electron-deficient olefins with NCS can be promoted by hypervalent iodine reagents. First, the NXS may react with TSNH2 to generate TsNHCl, which can be oxidized by PhI(OAc)2 to form I-N bond. The chloro anion can dissociate and the generated nitrenium intermediate can immediately react with the double bond of olefins to form an aziridinium ion. A series of substrates are tolerable under the reaction conditions and are aminochlorinated or brominated in good yields with high diastereoselectivities (eq 42). ... 

Hypervalent iodine species were demonstrated to have a pronounced catalytic effect on the metalloporphyrin-mediated oxygenations of aromatic hydrocarbons [93]. In particular, the oxidation of anthracene (114) to anthraquinone (115) with Oxone readily occurs at room temperature in aqueous acetonitrile in the presence of 5-20 mol% of iodobenzene and 5 mol% of a water-soluble iron(llI)-porphyrin complex (116) (Scheme 4.57) [93]. 2-ferf-Butylanthracene and phenanthrene also can be oxygenated under similar conditions in the presence of 50 mol% of iodobenzene. The oxidation of styrene in the presence of 20 mol% of iodobenzene leads to a mixture of products of epoxidation and cleavage of the double bond. Partially hydrogenated aromatic hydrocarbons (e.g., 9,10-dihydroanthracene, 1,2,3,4-tetrahydronaphthalene... 

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]. 

Aziridines are key structural motifs present in natural products such as mitomycins and azinomycins and versatile building blocks which can undergo various useful transformations. Hypervalent iodine-mediated intramolecular aziridinations of allylic carbamates and reaction of A-tosyliminophenyliodinane (Phi = NTs) with double bonds have been reported to be efficient and practical routes to access these three-membered rings. Allylic carbamates 71 undergo enantioselective aziridine formation on oxidation with chiral binaphthyl hypervalent iodine compound 72 (Scheme 28) [86]. 

Fries, J.L., Jeffrey, C.S., and Sorensen, E.J. (2009) A hypervalent iodine-induced double annulation enables a concise synthesis of the pentacydic core structure of the cortistatins. Oig. Lett., 11, 5394-5397. 

The reactions of selenocarbonyl compounds with electrophiles are also well-established procedures. Alkylations or acylations of the selenium atom of selenoamides409 or selenoureas410 are known. Selenonium salts are formed initially they can then be converted into diselenides, selenazoles, or cyclic selenides depending on their structure. Reactions of selenocarbonyls with bromine and iodine have also been widely exploited. Selenocarbonates, sele-nothiocarbonates,411-415 and selenoureas416-418 can be employed, the reaction of 209 with 1 equiv. bromine led to the hypervalent 10-Se-3 complex 210, whereas an excess of bromine gave rise to a cleavage of the carbon-selenium double bond and formation of product 211 (Scheme 64). 

The condensation of two molecules of primary selenoamides proceeds with bromine under extrusion of selenium to give selenadiazoles [93]. The reaction of selenocarbonates, selenothiocarbonates [94], and selenourea [95] with bromine and iodine has been widely tested. The products depend on the amount of halogen used. For example, in the reaction of N-methylthiazoline-2(3H)-selone, the use of one equivalent of bromine gives hypervalent lO-Se-3 complexes 44, whereas two equivalents of bromine cleave the carbon selenium double bond to give product 45. A similar hypervalent compound is formed from 4-imidazolin-2-selone,but the iodination of bis(imidazolin-2-selone)methane gives iodinated product 46. The availability of some of halogen adducts has been tested as a conducting material. 

---