Efficient oxidative ipso-fluorination of para-substituted phenols using pyridinium polyhydrogen fluoride in combination with hypervalent iodine(III) reagents

Diacetoxyiodobenzene (PIDA) and bis(trifluoroacetoxy)iodobenzene (PIFA) in the presence of pyridinium polyhydrogen fluoride (PPHF) are effective for the fluorination of para-substituted phenols to give a variety of 4-fluorocyclohexa-2,5-dienones in a good yield. (R,S)-1,1′-Bi-5,6,7,8-tetrahydro-2-naphthol (and its monoacetate) yields atropoisomeric fluorocyclohexadienones. The 4-substituted carbamate open-chain phenols were readily converted to fluorohydroindolenone and fluorohydroquinolenone derivatives by intramolecular conjugate addition.     

2-Iodoxybenzenesulfamides: new pseudobenziodoxole-based hypervalent iodine reagents

Amides of 2-iodoxybenzenesulfonic acid were prepared by the dioxirane oxidation of the corresponding 2-iodobenzenesulfamides and isolated as stable, microcrystalline products. These new representatives of the pseudocyclic hypervalent iodine compounds can selectively oxidize benzylic alcohols to aldehydes.     

Mechanistic aspects of alkene oxidation using chiral hypervalent iodine reagents

Recent progress in the area of hypervalent iodine-induced enantioselective oxidation is reviewed with emphasis from a mechanistic point of view. Chiral lactate and lactamide sidechains in hypervalent iodine reagents induce herical chirality around the iodine reaction site, which provides a chiral environment suitable for enantioselective transformations. The stereochemical outcomes of alkene oxidation are also compiled and used for systematically understanding the reaction mechanism of oxidative double bond difunctionalization.     

Electrophilic trifluoromethylation of arenes and N-heteroarenes using hypervalent iodine reagents

The reaction of hypervalent iodine trifluoromethylating reagents with a variety of arenes and N-heteroarenes gives access to the corresponding trifluoromethylated compounds. In comparative studies, 1-trifluoromethyl-1,3-dihydro-3,3-dimethyl-1,2-benziodoxole (2) proved to be the superior to 1-trifluoromethyl-1,2-benziodoxol-3-(¹H)-one (1) for the direct aromatic trifluoromethylation. Depending on the individual substrates, additives such as zinc bis(trifluoromethylsulfonyl)imide or tris(trimethylsilyl)silyl chloride proved helpful in promoting the reactions. In the case of nitrogen heterocycles a pronounced tendency for the incorporation of the trifluoromethyl group at the position adjacent to nitrogen was observed.     

An efficient route to 4-aryloxycoumarins via one-pot reactions of 4-hydroxycoumarins with hypervalent iodine reagents

Highly efficient reactions of 4-hydroxycoumarin with hypervalent iodine reagents under mild conditions are described, which give rise to 4-aryloxycoumarins in good to excellent yields.     

Direct C-H substitution reaction of anilides using hypervalent iodine and their regioselective issues

The direct C-H substitution reactions of anilides using hypervalent iodine proceeded to afford azide, chloro, bromo, and fluoro derivatives, and their regioselectivity were described. In the specific reaction conditions, the unique regioisomers were obtained.     

Efficient generation and trapping of acylbenzynes from hypervalent iodine compounds

[5-Acyl-2-(trimethylsilyl)phenyl]iodonium triflates were prepared for the generation of benzynes bearing ketone function. Treatment of the iodonium triflates with Bu₄NF in CH₂Cl₂ in the presence of furan at room temperature gave 6-acyl-1,4-epoxy-1,4-dihydronaphthalenes in high yields. The mild conditions and the tolerance of the ketone function on benzyne generation are attributable to the advantage of hypervalent iodine compounds.     

Oxidative rearrangement of alkenes using in situ generated hypervalent iodine(III)

A novel protocol for the oxidative rearrangement of alkenes using in situ generated hypervalent iodine(III) was developed. This approach uses inexpensive, readily available, and stable chemicals (PhI, mCPBA, and TsOH) giving rearrangement products in yields comparable to those obtained using the more expensive commercially available [hydroxy(tosyloxy)iodo]benzene [HTIB or Koser’s reagent]. Additionally, an alternative protocol for the synthesis of 1-methyl-2-tetralone through the one-step epoxidation/rearrangement of 4-methyl-1,2-dihydronaphthalene using mCPBA and TsOH was developed.     

Oxidation of 4-arylphenol trimethylsilyl ethers to p-arylquinols using hypervalent iodine(III) reagents

An efficient synthesis of p-arylquinols by the oxidation of 4-arylphenol trimethylsilyl ethers with phenyliodine(III) diacetate (PIDA) is reported. This protocol greatly improved the yield of p-quinol by minimizing oligomer side products compared to the oxidation of free phenol with hypervalent iodine(III) reagents. The innocuity of phenyliodine(III) diacetate associated with the mild conditions make the method highly competitive over metal-mediated oxidation reactions. The proposed reaction mechanism is discussed and compared to the generally accepted mechanism of 4-substituted phenols to explain the yield improvement.     

A novel and direct synthesis of chroman derivatives using a hypervalent iodine(III) reagent

The direct aromatic carbon-oxygen bond-formation reaction was described and the novel and simple synthetic method for chroman derivatives involving aromatic cation radical intermediates was developed using the hypervalent iodine(III) reagent, phenyliodine(III) bis(trifluoroacetate) (PIFA).     

Synthesis and reactivity of carbazole-containing hypervalent iodine(III) reagents

A range of bench-stable carbazole-containing hypervalent iodine(Ⅲ) reagents were synthesized by I-N bond formation in good yields.This kind of benziodoxolone reagents was used for a C-N coupling reaction to introduce a carbazole group to aromatic heterocycle compounds.     

Electrogenerated hypervalent iodine compounds as mediators in organic synthesis

1. Download : Download high-res image (130KB)
2. Download : Download full-size image

     

Recent progress in the electrochemistry of hypervalent iodine compounds

Hypervalent iodine compounds constitute a well-established and broadly used reagent family in organic synthesis. As they are usually either used in stoichiometric quantities or generated in situ from an aryl iodide precursor using a terminal oxidant, the associated waste and separation problems pose major challenges en route to sustainable and scalable processes. In this regard, the use of inexpensive electric current as a traceless oxidant for the in-situ generation of hypervalent iodine has emerged as a promising alternative. This review summarizes the advances over the past 2 years, including improved electrolysis protocols, new synthetic applications, and concepts for enhancing the sustainability of the reactions.     

Synthesis,characterization, and initial reaction study of two new bicyclic hypervalent iodine(III) reagents

The synthesis of two new bicyclic hypervalent iodine(III) reagents 5 and 6 is described along with their corresponding X-ray crystal structures for the first time. A detailed comparison in the bond lengths and bond angles of reported bicyclic hypervalent iodine(III) reagents is also presented. Furthermore, an initial study shows that these two hypervalent iodine(III) reagents could promote the dipeptide coupling reaction.     

Nucleophilic attack of intramolecular hydroxyl groups on electron-rich aromatics using hypervalent iodine(III) oxidation

The hypervalent iodine(III) reagent, phenyliodine bis(trifluoroacetate) (PIFA)-mediated oxidative nucleophilic substitution of electron-rich aromatics involving aromatic cation radical intermediates was utilized in the direct aromatic carbon-oxygen bond formation reaction, and a novel and simple synthetic method for chroman derivatives was developed. As an extension of this methodology, a facile access to spirodienone derivatives was also achieved.     

An unprecedented 7-membered ring enamide cyclization through hypervalent iodine phenolic oxidation

An unprecedented 7-membered ring cyclization of an enamide to a phenol through hypervalent iodine phenolic oxidation was discovered. In the process a molecule of solvent is incorporated on the cycle forming an unusual and stable hemi-aminal ether.     

New hypervalent iodine reagents for electrophilic trifluoromethylation and their precursors: synthesis, structure, and reactivity

Several new five- and a six-membered heterocyclic monochloroiodanes, including two cationic species, were synthesized. Three of which were used for the preparation of corresponding trifluoromethylation reagents. These compounds were characterized by X-ray crystallography for a comparative structural study. A reactivity study on the trifluoromethylation of para-toluenesulfonic acid has been conducted in order to compare initial rates. Compounds having a longer I-O bond display a higher reactivity.     

Enantiodifferentiating tetrahydrofuranylation of but-3-enyl carboxylates using optically active hypervalent iodine(III) reagents via a 1,3-dioxan-2-yl cation intermediate

Optically active methyl 2-[2-(diacetoxyiodo)phenoxy]propanoate and its derivative were prepared and used for oxygenation of but-3-enyl carboxylates leading to tetrahydrofuran-3-yl carboxylates as an enantiomerically enriched form.     

Electrophilic (phenylsulfonyl)difluoromethylation of thiols with a hypervalent iodine(III)-CF2SO2Ph reagent

A hypervalent iodine(III)-CF₂SO₂Ph compound (3) has been successfully prepared with selective nucleophilic reaction using PhSO₂CF₂SiMe₃ reagent, and this previously unkown compound 3 was found to act as a new electrophilic (phenylsulfonyl)difluoromethylation reagent for a variety of S-nucleophiles under very mild reaction conditions.