Hypervalent iodine reagents, direct

Under certain conditions, amides can add directly to alkenes to form N-alkylated amides. 3-Pentenamide was cyclized to 5-methyl-2-pyrrolidinone by treatment with trifluorosulfonic acid. Acylbydrazine derivatives also cyclized in the presence of hypervalent iodine reagents to give lactams. When a carbamate was treated with Bu3SnH, and AIBN, addition to an alkene led to a bicyclic lactam. 

Olefins can directly be functionalized to cyclic sulfates using a hypervalent iodine reagent (86TL3971, 86ZOR450) [Eq. (12)]. 

The direct chlorination of iodoarenes 9 and 11 has been used for the preparation of 4,4 -bis(dichloroiodo)biphenyl (10) and 3-(dichloroiodo)benzoic acid (12) (Scheme 2.4), which are convenient recyclable hypervalent iodine reagents (Section 5.3) [66]. 

Iodine in combination with [bis(acyloxy)iodo]arenes is a classical reagent combination for the oxidative iodination of aromatic and heteroaromatic compounds [99], A typical iodination procedure involves the treatment of electron-rich arenes with the PhI(OAc)2-iodine system in a mixture of acetic acid and acetic anhydride in the presence of catalytic amounts of concentrated sulfuric acid at room temperature for 15 min [100,101]. A solvent-free, solid state oxidative halogenation of arenes using PhI(OAc)2 as the oxidant has been reported [102]. Alkanes can be directly iodinated by the reaction with the PhI(OAc)2-iodine system in the presence of f-butanol under photochemical or thermal conditions [103]. Several other iodine(in) oxidants, including recyclable hypervalent iodine reagents (Chapter 5), have been used as reagents for oxidative iodination of arenes [104-107]. For example, a mixture of iodine and [bis(trifluoroacetoxy)iodo]benzene in acetonitrile or methanol iodinates the aromatic ring of methoxy substituted alkyl aryl ketones to afford the products of electrophilic mono-iodination in 68-86% yield [107]. 

A simple method for the preparation of a-azido ketones and esters 500 in good yields by direct azidation of carbonyl derivatives 499 at the a-carbon using 4,4 -bis-(dichloroiodo)biphenyl and sodium azide has been reported (Scheme 3.198) [575]. The hypervalent iodine reagent, 4,4 -bis-(dichloroiodo)biphenyl, can be easily recycled from the reaction mixture. 

Hypervalent aryl iodine reagents have also been used as the electrophile in direct ary-lation reactions. In these examples, the strongly oxidizing hypervalent iodine reagents are proposed to react with the intermediate Pd(II) species to generate a Pd(IV) intermediate. Subsequent reductive elimination of biaryl from this Pd(IV) intermediate is then believed to regenerate the active Pd(II) species (Equation 19.141). ... 

Although the majority of direct arylations have been catalyzed by palladium, rhodium, and ruthenium, some additional studies have also focused on direct arylations catalyzed by first-row metals, such as iron and copper. For example, an iron-catalyzed direct arylation reaction between arylzinc reagents and 2-arylpyridine derivatives has been reported (Equation 19.146). Several direct couplings of heteroarenes with aryl halides (Equation 19.147) or hypervalent iodine reagents ° catalyzed by copper halides have also been reported. 

Waser and et al. developed a C2-selective direct alkynylation of indoles (174, 66% yield).The reaction, which runs under air at room temperature, relies on a palladium catalyst and hypervalent iodine reagent, triisopro-pylsilylethynyl-l,2-benziodoxol-3(lFJ)-one. The indole ring may be... 

Similar direct arylations have been accomplished using hypervalent iodine reagents and the Herrmann-Beller catalyst 4 (Scheme 24.11) [ 15]. This method is applicable toward the phenylation of electron-neutral and electron-rich arene substrates and provides the products in modest to good yields. Increasing steric hindrance on the arene moiety leads to decreased product yields. An isomeric mixture of products is obtained, and the selectivity for phenylation of xylenes is similar to the transformations in Scheme 24.9. 

Progress in this field was accomplished through the development of new hypervalent iodine reagents. Because of the enhanced solubility of the reported 2-methoxyphenyliminoiodane motif 42 from Nemykin and Zhdankin [32], this reagent allowed for the development of various direct amination reactions of silyl enol ethers 112 to products 113 in good yields and within short reaction times (Scheme 25). The general reaction conditions call for the activation with a... 

In addition, the reaction between hypervalent iodine reagents such as iodosyl-benzene or its diacetate derivative with molecular iodine has been employed frequently in aliphatic amination reactions. These processes start from an initial formation of an alkyl hypoiodite derivative, which can promote subsequent radical amination pathways. An excellent use of this concept is the Suarez methodology for the generation of diversified aminated carbohydrate structures [80-86]. Although the hypervalent iodine reagent is not directly involved in the amination reaction, the efficiency of the method deserves mentioning within the present chapter. It was recently extended to catalytic transformations [87],... 

Niedermann KM (2012) Direct trifluoromethylation of organonitrogen compounds with hypervalent iodine reagents. Dissertation ETH no. 20465, ETH Zurich. doi 10.3929/ethz-a-007567196... 

Niedermann K, Friih N, Senn R, Czamiecki B, Verel R, Togni A (2012) Direct electrophilic N-trifluoromethylation of azoles by a hypervalent iodine reagent. Angew Chem Int Ed 51 6511-6515. doi 10.1002/anie.201201572... 

Stereoselective carbon-carbon bond formations with hypervalent iodine reagents are also prominently described in the literature. Direct asynunetric a-arylation reactions are not easy to perform. Ochiai et al. synthesized chiral diaryliodonium salts such as [l,l -binaphthalen]-2-yl(phenyl)iodonium tetrafluoroborate derivatives 21 via a BFs-catalyzed tin-X -iodane exchange reaction and developed the direct asymmetric a-phenylation of enolate anions derived from cyclic p-ketoesters (Scheme 7) [37]. A beautiful example of direct asymmetric a-arylation of cyclohexanones in the course of a natural product synthesis was presented through the desymmetrization of 4-substituted cyclohexanones using Simpkin s base, followed by coupling with diaryliodonium salts [38]. Other binaphthyl iodonium salts related to 21 have also been reported [39]. 

The direct palladium-catalyzed C3-alkynylation of free indoles with bromoacety-lenes was first described by Gu and Wang in 2009. The C2-selective alkynylation of indole proved to be especially challenging, and this was not realized until Waser et al. described a mild protocol using TIPS-protected hypervalent iodine reagent 101 and a palladium(II) catalyst (Scheme 10.34). Under optimized conditions, a variety of 7V-alkylated indoles 100 could undergo the alkynylation reaction via a palladium(II)/palladium(IV) mechanism to afford products 102-106 in moderate to good yields. It is unknown whether the C2-palladated intermediate is formed as result of a CMD mechanism, or via a pathway of electrophilic palladation at C3 followed by metal migration to C2. 

N.C. Jadhav, P.B. Jagadhane, H.V. Patile, V.N. Telvekar, Three-component direct synthesis of substituted p)frroles from easily accessible chemical moieties using hypervalent iodine reagent. Tetrahedron Lett. 54 (2013) 3019-3021. 

Considerable interest has been expressed in the development of direct methods for the synthesis of a-hydroxy ketones using nontoxic hypervalent iodine reagents and which involve the foUowing methods reaction of a ketone with iodobenzene diacetate in the presence of potassium hydroxide in methanol and then hydrolysis of the dimethylacetals oxidation of the enol sUyl ether of acetophenone using the s) tem iodosobenzene/boron trifluoride efherate/water in methylene chloride at—40°C and reaction of ketones with [fcis(trifluoroacetoxy)]iodobenzene and trifluoroacetic acid in acetonitrile-water under acidic conditions. "... 

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