Hypervalent iodine: a powerful electrophile for asymmetric α-functionalization of carbonyl compounds.

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REVIEW

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Hypervalent iodine: a powerful electrophile for asymmetric α-functionalization of carbonyl compounds Dao-Qing Dong,a Shuang-Hong Hao,a Zu-Li Wang*a and Chao Chen*b Environmentally friendly hypervalent iodine reagents are unusually effective promoters of asymmetric

Received 12th February 2014, Accepted 21st April 2014

α-functionalization of carbonyl compounds. By using hypervalent iodine reagents, various substituents

DOI: 10.1039/c4ob00318g

can be introduced into the α-position of carbonyl compounds. In the present review, we briefly survey the asymmetric α-functionalization of carbonyl compound reactions catalyzed by these hypervalent

www.rsc.org/obc

iodine reagents.

1.

Introduction

Hypervalent iodine reagents have received considerable attention in recent years. They are efficient alternatives to the toxic heavy-metal-based oxidants and expensive organometallic catalysts in many organic transformations. Low toxicity, a favourable safety profile, ease of handling, and an environmentally benign nature make them particularly attractive for metal-free

a

College of Chemistry and Pharmaceutical Sciences, Qingdao Agricultural University, Qingdao 266109, People’s Republic of China. E-mail: [email protected]; Fax: (+86)-532-8608-0213; Tel: (+86)-532-8608-0213 b Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, People’s Republic of China. E-mail: [email protected]; Tel: (+86)-10-6277-3684

Dao-Qing Dong was born in Shandong province. She received her B.S. from Qingdao Agricultural University in 2006 and M.S. from Hangzhou Normal University. Her research interests include organic synthesis and C–H bonds activation.

Dao-Qing Dong

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reactions.1 Many different reactions including alkene dioxygenation,2 α-functionalization of carbonyl compounds,3 oxidative dearomatization of phenols4 and so on have been performed in the presence of hypervalent iodine as electrophiles or oxidants. Several comprehensive reviews5 and books6 have been published on the topic of hypervalent iodine chemistry. Among these hypervalent iodine-participated reactions, hypervalent iodine-catalyzed asymmetric α-functionalization of carbonyl compounds has become a powerful tool for the synthesis of chiral α-functionalized carbonyl compounds. Because chiral α-functionalized carbonyl compounds are versatile building blocks and pivotal intermediates in organic synthesis, more and more attention has been paid to asymmetric α-functionalization of carbonyl compounds induced by hypervalent iodine species. While there have been many papers

Shuang-Hong Hao was born in Shaanxi province (China). He graduated with a master’s degree (2000) and Ph.D. degree (2005) in chemistry of pesticides from Northwest Agriculture and Forestry University of Science and Technology. He worked as a research professor (2011–2012) in organic chemistry at Kansas State University in the group of Prof. Duy H. Hua. He is currently Associate Professor at Qingdao Shuang-Hong Hao Agricultural University. His research interests include the design and synthesis of new compounds with pharmaceutical and pesticidal activity.

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reporting these reactions, this would be the first review especially on asymmetric α-functionalization of carbonyl compounds using hypervalent iodine species. The challenges and opportunities for these reactions will be discussed with the willingness to promote the development of hypervalent iodine chemistry.

2. Achiral hypervalent iodineparticipated asymmetric α-functionalization of carbonyl compounds in combination with chiral organocatalysts 2.1.

α-Hydroxylation

Optically active α-hydroxy carbonyl moieties are commonly found in lots of important natural products and bioactive molecules.7 The methods for their enantioselective synthesis have received more and more attention in recent years.8 In 2005, Córdova and co-workers9 realized the direct organocatalytic asymmetric α-oxidation of ketones with moderate ee values. In the presence of iodosobenzene as an oxidant and L-proline as a catalyst, several ketones can be oxidized to the desired products, but the yields of this reaction were not very high (Scheme 1). The stereochemical outcome of the reaction may come from re-facial attack on the catalytically generated enamine by the oxygen of PhIO, which is subsequently protonated by the acid moiety of L-proline to furnish the α-hydroxylated ketone (Scheme 2). 2.2.

Aziridination

The aziridine moiety represents one of the most valuable three-membered ring systems in organic synthesis.10 The highly regio- and stereoselective transformations of the aziridine derivatives constitute a powerful approach toward the

Zu-Li Wang

Zu-Li Wang was born in Shandong province (China). After he graduated with a master’s degree in organic chemistry from Huaibei Normal University, he obtained his Ph.D. degree (2012) in organic chemistry from Tsinghua University under the supervision of Prof. Mei-Xiang Wang. He is currently Associate Professor at Qingdao Agricultural University. His research interests include C–H, C–O bonds activation and asymmetric catalysis.


Scheme 1 Organocatalytic asymmetric α-oxidations of ketones with iodosobenzene.

Scheme 2

Proposed state.

preparation of a large variety of functionalized nitrogen-containing target compounds.11 In the presence of [N-( p-toluenesulfonyl)imino]phenyliodinane (PhIvNTs) as a nitrene source, the highly enantioselective aziridination of chalcones catalysed by chiral 1,8-bisoxazolinylanthracene (AnBOX) and CuOTf was described by Xu and co-workers.12 The chalcones with electron-donating substituents show higher enantioselectivities than those with electron-withdrawing substituents. The coordination of copper in the catalyst and the oxygen atom of the carbonyl group in chalcones seems to play an important role in the high enantioselectivity of the asymmetric aziridination (Scheme 3).

Associate Prof. Dr Chen graduated from the Department of Chemistry in Tsinghua University with a B.S. degree in 2001. Then he began to pursue his Ph.D. in organic chemistry there. In 2006, he obtained his Ph.D and then went to the Organic Chemistry Institute, Muenster University (Germany). He worked there as a postdoc researcher funded by “Alexander von Humboldt Foundation”. In May 2011, he Chao Chen joined the faculty of the Department of Chemistry in Tsinghua University as an associate professor. Now his research is mainly focused on polyvalent iodine and borane chemistry in organic synthesis.

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Scheme 3

Scheme 4


Asymmetric aziridination of chalcones.

Organocatalytic epoxidations with iodosobenzene.

Scheme 6

Proposed mechanism.

Asymmetric aziridination of chalcones.

In 2005, the same research group disclosed another example13 of aziridination of chalcones. Under the catalysis of CuOTf and cyclohexane-linked bis-oxazolines (cHBOXes), the products were obtained with up to >99% ee. Unlike 1,8-anthracene-linked bis-oxazolines (AnBOXes), here the enantioselectivity is not substituent-dependent with respect to chalcones in this system (Scheme 4). 2.3.

Scheme 5

Epoxidation

The enantioselective catalytic oxidation of olefins is one of the most powerful transformations in organic synthesis.14 There has been an ever-increasing demand for highly efficient and predictable access to enantioenriched oxiranes. Using hypervalent iodine reagents as oxidants, MacMillan et al. reported the asymmetric epoxidation15 of α,β-unsaturated aldehydes with an imidazolidinone catalyst. NMR studies (15N) revealed that the slow, in situ production of monomeric iodosobenzene (PhIvO) from NsNIPh is essential to alleviating losses in catalytic efficiency. It is important to note that the functionalities that are often susceptible to oxidation such as electrondeficient amines, electron-rich olefins and so on were well compatible in this system (Scheme 5). A mechanism of this reaction15 was proposed: firstly, a chiral amine reacts with 5 to produce iminium 2, and then a nucleophilic oxygen that is incorporated into a suitable leaving group could add with selectivity to an iminium 2; subsequently, enamine 3 formation occurs followed by intramolecular trapping of the pendant electrophilic oxygen with concomitant expulsion of the oxygen tethered leaving group, and 4 is formed. Finally, the desired products and the catalyst 1 are produced by hydrolysis of 4 (Scheme 6).

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2.4.

α-Alkynylation

The chemistry of acetylenes has been extensively used in organic synthesis.16 In 2010, Waser and co-workers developed the asymmetric ethynylation of ketoesters17 in the presence of hypervalent iodine reagents. Using the phase transfer catalyst, only moderate asymmetric induction was achieved, leaving large room to be explored (Scheme 7). This method gave access to quaternary centers with four different carbon substi-

Scheme 7

Asymmetric alkynylation of ketoester.


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Scheme 8

Review

Possible mechanisms for the ethynylation reaction.

tuents which are a synthetically challenging class of compounds in organic chemistry. The reaction may proceed through a 1,2-hydride-shift mechanism after the investigation of the C13-labeled experiment: firstly, conjugate addition of ketoesters to the alkyne occurred to produce 3 and then an elimination and 1,2-hydride shift occurred to form the final products 5 (Scheme 8). 2.5.

α-Chlorination

Togni et al. showed for the first time that the highly reactive hypervalent dichloroiodine compound can be employed in a catalytic asymmetric chlorination18 of β-ketoesters. Chlorinated products with up to 71% ee were obtained using the [Ti(TADDOLato)] complex as a chiral catalyst. The enantioselectivity of the reaction shows a remarkable temperature dependence, and the maximum selectivity was obtained at 50 °C (Scheme 9). 2.6.

α-Arylation

The catalytic asymmetric α-arylation of carbonyl compounds is of high interest, because it provides efficient access to optically active α-aryl compounds which are regarded as essential motifs in many biologically active natural products and pharmaceutically active compounds.19 In 2011, MacMillan and co-workers disclosed the enantioselective α-arylation of aldehydes which was performed using diaryliodonium salts and a combination of copper and organic catalysts.20a This transformation can be applied to the rapid synthesis of (S)-ketoprofen, a well-established and commer-

Scheme 9

Catalytic asymmetric chlorination of β-ketoesters.


Scheme 10

Enantioselective α-arylation of aldehyde.

cially successful medicinal agent (Scheme 10). A proposed mechanism of this reaction was proposed by MacMillan et al. and is shown in Scheme 11. The π-Cu complex 4 is formed between the coordination of the highly electrophilic Cu(III) aryl system 3 (from oxidative addition of Cu(I) to the C–I bond of the diaryliodonium triflate system) and the activated chiral enamine 2 (condensation of amine catalyst 1 with the aldehyde substrate). Subsequently, the rapid bond isomerization leads to the η1-iminium 5 organocopper, which upon reductive elimination should release the optically enriched α-aryl iminium 6 and the Cu(I)Br catalyst. The organocatalyst partner 1 along

Scheme 11

Hypothesis for the α-arylation of aldehydes.

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Scheme 12 Enantioselective α-arylation of carbonyls via Cu(I)-bisoxazoline catalysis.

with the desired α-aryl aldehyde product finally formed by hydrolysis of iminium 6. Besides aldehyde, lactones and acyl oxazolidones can also be arylated using a combination of diaryliodonium salts and copper catalysis by the same group (Scheme 12).20b Chiral copper(III) species may be incorporated in the catalytic cycle. This method provides a valuable synthon for the production of medicinal agents. Gaunt and co-workers found that copper(II)-bisoxazoline complexes and diaryliodonium salts20c were also effective for the catalytic enantioselective α-arylation of N-acyloxazolidinones (Scheme 13). But the mechanism of this reaction was not clear. The authors thought that copper(III)-mediated aryl transfer was more likely for this reaction. In 2005, a direct asymmetric α-arylation of cyclohexanones was disclosed by Aggarwal and co-workers.20d Simpkin’s base was used to desymmetrize 4-substituted cyclohexanones and then a coupling reaction with diaryliodonium salts occurred to afford 2-aryl ketones with high enantioselectivities (Scheme 14). This approach can be used for the synthesis of (+)-epibatidine. Feng and co-workers found that chiral Lewis acid catalysts of N,N′-dioxide-Sc(OTf )3 complex performed well in the reaction of N-unprotected 3-substituted oxindoles with diaryliodonium triflates under mild reaction conditions. The arylated products with quaternary carbon centers were afforded in high

Scheme 13

Enantioselective α-arylation of N-acyloxazolidinones.

Scheme 14

Enantioselective α-arylation of cyclohexanones.

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Scheme 15

α-Arylation of N-unprotected 3-substituted oxindoles.

enantioselectivity and reactivity (up to 99% ee and 99% yield). An antiproliferative agent could be synthesized using this method (Scheme 15).21 2.7.

α-Alkylation

In 2008, Gaunt and co-workers22 reported the intramolecular α-alkylation of aldehyde using an oxidative dearomatization strategy. A range of highly functionalized polycyclic molecules with excellent selectivities were formed in this reaction. The process of this reaction involves oxidative dearomatization of substituted phenols followed by asymmetric intramolecular Michael addition catalysed by a desymmetrizing secondary amine (Scheme 16).

Scheme 16

Catalytic asymmetric α-alkylation of aldehyde.


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Scheme 17 aldehyde.

Non-oxygen

nucleophiles

Review

used

for

α-alkylation

of

In addition, non-oxygen nucleophiles could also participate in this reaction. For example, –CN and –F acted as a nucleophile to form the desired products (Scheme 17). This reaction that can directly transform an aromatic motif into the non-racemic structure would provide a powerful strategy for the rapid chemical synthesis of complex molecules. 2.8.

α-Trifluoromethylation and trifluoromethylthiolation

The incorporation of fluorine into organic molecules often triggers significant changes in the physical, chemical, and biological properties of the molecules.23 As a result, developing methodologies to introduce fluoroalkyl groups into organic compounds has become one of the hottest topics in organic transformations.24 In 2010, the enantioselective α-trifluoromethylation of aldehydes was reported by MacMillan and coworkers (Scheme 18).25 By using commercially available, bench-stable reagents and catalysts, a wide range of functional groups such as aryl rings, ethers, esters, carbamates, and imides were well tolerated in this reaction. The mechanism of this reaction is described in Scheme 19. The reaction between electrophilic iodonium salt 2 (generated from 1 through Lewis

Scheme 18

Catalytic enantioselective α-trifluoromethylation.


Scheme 19

Proposed mechanism for direct α-trifluoromethylation.

acid-catalyzed bond cleavage) and chiral enamine 4 (generated from the condensation of amine catalyst 3 with an aldehyde substrate) would result in λ3-iodane species 5. Then λ3-iodane species 5 undergoes reductive elimination with stereoretentive alkyl transfer to form the iminium ion 6. Finally the hydrolysis of the iminium ion 6 would liberate the imidazolidinone catalyst 3 along with the desired α-CF3 products. Besides aldehyde, chiral imide enolates26 can also undergo diastereoselective α-trifluoromethylation with a hypervalent iodine-CF3 reagent to afford the desired products with up to 91% yield. But the ee value of this reaction was not very high. The resulting isolated products could be further transformed into valuable products without racemization (Scheme 20). Recently, Gade and co-workers27 demonstrated an efficient method for enantioselective trifluoromethylation of cyclic β-ketoesters using commercially available reagents via the merging of Cu–boxmi catalysis. Both five- and six-membered ring β-ketoesters can be converted to the corresponding products in high yields with up to 99% ee under mild conditions. Furthermore, the products can be transformed diastereoselectively to α-CF3 β-hydroxyesters with two adjacent quaternary stereocenters via a Grignard reaction (Scheme 21). The first highly enantioselective trifluoromethylthiolation of β-ketoesters28 catalyzed by a chiral Lewis base or a phasetransfer catalyst was presented by Shen et al. This reaction con-

Scheme 20 reagent.

α-Trifluoromethylation with a hypervalent iodine-CF3

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Scheme 21

Scheme 22


Enantioselective trifluoromethylation of β-ketoesters.

Enantioselective azidation of β-keto esters.

Scheme 24

Enantioselective vinylation.

Asymmetric trifluoromethylthiolation of β-ketoesters.

stitutes a practical and broadly applicable approach toward chiral building blocks with quaternary stereocenters that bear an SCF3 group (Scheme 22). 2.9.

Scheme 23

Azidation

Using a readily available and stable azidoiodinane as an N3transfer reagent, Gade and co-workers29 demonstrated the first Fe-catalyzed enantioselective azidation of β-keto esters and oxindoles. By the combination of an iron(II) chlorido complex and silver carboxylate, cyclic β-keto esters were converted to the corresponding products in high yields with up to 93% ee. In addition, using the catalyst prepared from iron(II) propionate and the ligand in situ, 3-substituted 3-azidooxindoles with high enantioselectivities (up to 94%) can be obtained (Scheme 23).

direct route to the enantioselective construction of enolizable α-formyl vinylic stereocenters without racemization or olefin transposition (Scheme 24).

3. Chiral hypervalent iodineparticipated asymmetric α-functionalization of carbonyl compounds 3.1.

2.10. Vinylation Synergistic catalysis, wherein two catalysts and two catalytic cycles work in concert to create a single new bond, has emerged as a powerful mechanistic approach to asymmetric reaction engineering.30 MacMillan and co-workers realized the enantioselective α-trifluoromethylation25 and α-arylation20a of aldehydes via the synergistic combination of copper catalysis, organocatalysis, and iodonium salts. In 2012, they described the enantioselective α-vinylation of aldehydes using vinyl iodonium triflate salts via the synergistic combination of copper and chiral amine catalysis.31 These mild catalytic conditions provide a

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α-Arylation

Chiral diaryliodonium salts, 1,1′-binaphthyl-2-yl( phenyl)iodonium tetrafluoroborates and their derivatives were first synthesized32 by Ochiai and co-workers. When they were subjected to the asymmetric α-phenylation of enolate anions derived from cyclic β-ketoesters, the desired products with moderate ee values were obtained. Unlike MacMillan’s work,20a,b the asymmetric α-arylation reaction can be realized using only a chiral hypervalent iodine reagent, and an amine or an ammonium catalyst was not needed (Scheme 25). In 2013, Wirth and co-workers described the first stereoselective rearrangement of aryl substituted alkenes with high enantioselectivities mediated by chiral lactic acid-based iodine(III)


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Scheme 25

Review

Asymmetric phenylation of the β-keto ester.

Scheme 27

Scheme 26

Enantioselective oxidative cycloetherification.

Stereoselective rearrangement of aryl substituted alkenes.

reagents. A wide range of carbonyl compounds were arylated efficiently with high stereoselectivity in this system (Scheme 26).33 3.2.

α-Oxidation

In the presence of in situ-generated chiral quaternary ammonium (hypo)iodite salts as catalysts, an enantioselective oxidative cycloetherification of ketophenols to 2-acyl-2,3-dihydrobenzofuran derivatives was realized by Ishihara and coworkers with hydrogen peroxide as an environmentally benign oxidant.34 Notably, tetrabutylammoniumbromide or chloride was not effective for this reaction. The substituents at the 3,3′positions of the binaphthyl moiety were crucial for the enantioselectivity and the chemical yield. Ammonium cations bearing bulky and electron-deficient substituents {Ar = 3,5[3,5-(CF3)2C6H3]C6H3} at the 3,3′-positions gave the best results (Scheme 27A). Mechanism studies implied that chiral quaternary ammonium hypoiodite ([R4N]+[IO]−) or iodite ([R4N]+[IO2]−), which should be generated in situ from ammonium iodide (R4NI) and a co-oxidant, was involved in the catalytic cycle (Scheme 27B). In the same year, a series of enantiomerically pure iodoarenes35 were synthesized by Wirth et al. Then they were employed for the lactonization of 5-oxo-5-phenylpentanoic acid with m-CPBA as a stoichiometric oxidant. However, the


Scheme 28 Iodoarenes propiophenone.

as

catalysts

in

the

α-oxytosylation

of

yield and ee value of this reaction were not very high. p-TsOH·H2O was necessary for this reaction due to the fact that a ligand exchange at the hypervalent iodine species was needed to form an active catalyst (Scheme 28). These compounds can also be used as catalysts in the α-oxytosylation of propiophenone. In 2012, Moran and co-workers disclosed the enantioselective oxidative cyclization36 of 5-oxo-5-phenylpentanoic acid to 5-benzoyldihydrofuran-2(3H)-one in the presence of

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Scheme 29 Enantioselective oxidative cyclization of 5-oxo-5-phenylpentanoic acid. Scheme 32

chiral aryl iodides as catalysts. The highest enantioselectivity of 51% ee was obtained. This is the highest selectivity recorded to date for this reaction (Scheme 29). 3.3.

α-tosyloxylation

In 1997, asymmetric oxytosylation of ketones in the α-position was realized by Wirth and co-workers37 with chiral hypervalent iodine compounds. Despite trying several chiral hypervalent iodine reagents, the yield and enantioselectivity were still not satisfactory (Scheme 30). The next year, the same group synthesized other chiral hypervalent iodine compounds and subjected them to the reaction of α-oxytosylation38 of ketones (Scheme 31). But the ee value of this reaction still needs to be improved.

Scheme 30

Asymmetric oxytosylations of ketones.

Scheme 31

α-Oxytosylation of propiophenone.

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Asymmetric α-oxytosylation of propiophenone.

In 2001, a series of ortho-substituted chiral hypervalent iodine reagents were synthesized by Wirth and co-workers.39 The evaluation of these new compounds as stereoselective electrophilic reagents towards ketones was attempted and enantioselectivities up to 40% were achieved (Scheme 32). All of the examples mentioned above suffered from the drawback that chiral hypervalent iodine reagents must be present in stoichiometric quantities. In 2007, Wirth et al.40 disclosed the first α-oxytosylation of ketones catalysed by a catalytic amount of enantioenriched iodoarenes using m-CPBA as a stoichiometric oxidant (Scheme 33). Two mechanisms were proposed for this reaction. After the formation of the iodane 2, the reaction between 2 and the enol tautomer (unknown geometry) of propiophenone occurred to give 3 (Path A). Then the desired products were produced from the SN2 reaction of 3 with tosylate. Alternatively, 4 was produced through Path B, and then SN2 reaction occurred to yield the final products (Scheme 34). Subsequently, Wirth and co-workers reported other examples of α-oxytosylation of ketones, but the enantioselectivities are still not very high.41,42 In 2011, a series of spirobiindane scaffold-based chiral iodoarenes43 were synthesized. The evaluation of these new chiral iodoarenes as catalysts in the enantioselective α-tosyloxylation of ketones was performed using m-CPBA as a stoichiometric oxidant, and the desired products with up to 58% enantiomeric excess were obtained. The acidity of TsOH may

Scheme 33

Enantioselective oxytosylation of ketones.


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Review

Scheme 36 Scheme 34

α-Oxytosylation of propiophenone.

Possible mechanisms for the α-oxytosylation.

Several other chiral aryl iodides were prepared36 from the corresponding acid chlorides through either esterification or amidation reactions by Moran and co-workers. When they were assessed as catalysts in the α-oxytosylation of propiophenone, the desired products with up to 18% ee were obtained (Scheme 36). Legault et al. found that a drastic enhancement44 in catalytic activity was observed by the introduction of steric hindrance ortho to the iodine atom of the catalysts used for the α-tosyloxylation of ketones. Also structural analysis and density functional theory calculations were conducted to improve this acceleration effect. These results expanded the applicability of the hypervalent twist concept initially proposed by Goddard in iodine(V) chemistry and demonstrated that the Lewis bases

Scheme 35 Enantioselective α-tosyloxylation of ketones catalyzed by spirobiindane chiral iodoarenes.

lead to a slight racemization of the products (Scheme 35A). Koser-type iodane generated in situ from chiral iodoarene may be incorporated in the catalytic cycle (Scheme 35B).


Scheme 37

Catalytic enantioselective α-tosyloxylation of ketones.

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that would result in inactive catalysts were compatible with this system. Subsequently, Legault and co-workers synthesized a series of iodooxazoline catalysts45 to promote α-tosyloxylation of ketone derivatives. Computational chemistry was used to rationalize the stereoinduction process (Scheme 37A). Upon oxidation, the iodane center can be coordinated by the oxazoline. This was the best level of activity and selectivity recorded to date for this transformation (Scheme 37B).

4.

Conclusion

This review summarized the hypervalent iodine-participated α-functionalization of carbonyl compounds. Significant advances have been achieved in these transformations. The development and use of chiral hypervalent iodine reagents show great potential in organic synthesis. Although great progress has been achieved, some challenges still need to be addressed in order to accelerate the development of these reactions. Examples with high enantioselectivities are still rare, and the reaction conditions need to be optimized to meet the demands of high yields and enantioselectivities; many more types of chiral hypervalent iodine reagents and hypervalent iodine-participated asymmetric reactions need to be developed; mechanistic understanding of these reactions also deserves our attention. We are confident that this review will result in more investigations in the future to meet some of these challenges.

Acknowledgements Financial support from the Research Fund of QingDao Agricultural University’s High-Level Person [631303], the Scientific Research Foundation of Shandong Province Outstanding Young Scientist Award [BS2013YY024], the National Natural Science Foundation of China (21102080) and the Tsinghua University Initiative Scientific Research Program (2011Z02150) is gratefully acknowledged. We thank Qi-Qiang Wang, Xue-Yan Zhang and Wen-Hui Zhao for helpful discussions and for polishing the language.

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Asymmetric Synthesis with Hypervalent Iodine Reagents.

Advances in Synthetic Applications of Hypervalent Iodine Compounds.

Hypervalent iodine-mediated selective oxidative functionalization of (thio)chromones with alkanes.

Hypobromous acid, a powerful endogenous electrophile: Experimental and theoretical studies.

Electrophilic alkynylation of ketones using hypervalent iodine.

Chiral hypervalent iodine reagents: synthesis and reactivity.

Thioamination of Alkenes with Hypervalent Iodine Reagents.

Isostrychnine synthesis mediated by hypervalent iodine reagent.

The I=X (X=O,N,C) double bond in hypervalent iodine compounds: is it real?

Structurally Defined Molecular Hypervalent Iodine Catalysts for Intermolecular Enantioselective Reactions.

Cyclic Hypervalent Iodine Reagents for Atom-Transfer Reactions: Beyond Trifluoromethylation.

Facile oxidative rearrangements using hypervalent iodine reagents.

Reactivity of hypervalent iron with biological compounds.

Mild hypervalent iodine mediated oxidative nitration of N-aryl sulfonamides.

Hypervalent iodine reagent mediated reaction of [60]fullerene with amines.

iridium(I)-catalyzed asymmetric hydrogenation of cyclic α-alkylidene carbonyl compounds.

Lithium binaphtholate-catalyzed asymmetric addition of lithium acetylides to carbonyl compounds.

Addition of CF3 across unsaturated moieties: a powerful functionalization tool.

Synthesis of Scyphostatin Analogues through Hypervalent Iodine-mediated Phenol Dearomatization.

Halogen bonding in hypervalent iodine and bromine derivatives: halonium salts.

Electrophilic trifluoromethylation by use of hypervalent iodine reagents.

Electrophilic trifluoromethylthiolation of carbonyl compounds.

Oxidative Heterocycle Formation Using Hypervalent Iodine(III) Reagents.

Enantioselective Oxidative Rearrangements with Chiral Hypervalent Iodine Reagents.