Published papers

Molecular oxygen serves as a useful oxidant for the glycol scission of 1,2-diols and the Hofmann rearrangement of primary amides using pentamethyliodobenzene as a catalyst. The use of isobutyraldehyde and Lewis basic nitriles under O2 enabled the iodine(i)/(iii) catalytic cycle, where in situ-generated peracid acts as a terminal oxidant.

Pyrolysis of bis(perfluoroalkanesulfonyl)bromonium ylides in various olefins results in highly stereospecific formation of cyclopropanes via unimolecular decomposition. Product analysis, kinetic study, substituent effects, and theoretical study revealed the generation of singlet bis(perfluoroalkanesulfonyl)carbenes stabilized by intramolecular coordination of sulfonyl oxygen.

Because of its hyper-leaving ability, as well as its strong oxidizing ability, diaryl(triflato)-λ3-iodane transfers one of the aryl groups to iodoarenes simply upon gentle heating (>85 °C) in nonpolar solvents. We have performed an in-depth mechanistic study of this unusual aryl transfer reaction. A combination of experimental (product analysis, kinetic study, and substituent effects) and density functional theoretical approaches revealed that the reaction proceeds through a concerted bimolecular transition state, in which ipso-carbon binds loosely to both iodine centers. We also evaluated electronic effects on the thermodynamic stability of diaryl-λ3-iodanes.

A simple method for direct metal-free C-H amination of unactivated hydrocarbons using easy-handling diacetoxy-λ3-bromane and triflylamide or sulfamate esters was developed. The high 2°/3° regioselectivities and deuterium isotope effects suggest a concerted organonitrenoid transition state, analogous to C-H amination with N-triflylimino-λ3-bromane. This journal is

Hypervalent N-triflylimino-λ3-bromane undergoes direct and regioselective α-C-H amination of ethers at room temperature under transition metal-free conditions. Kinetic results, substituent and deuterium isotope effects suggest an asynchronous concerted organonitrenoid transition state with some hydride transfer character, analogous to that for alkane C-H insertions. © 2012 Royal Society of Chemistry.

The iodoform reaction has long been used as a qualitative test for acetyl and/or ethanol units in organic molecules. However, its synthetic applications are quite limited. Here, we describe a tuned iodoform reaction for oxidative demethylation reaction with I2 and t-BuOK in t-BuOH, in which in situ-generated t-BuOI serves as the chemoselective iodinating agent. This system enables one-step conversion of levulinic acid to succinic acid, a major four-carbon chemical feedstock. This oxidative demethylation is also applicable to other compounds containing an acetyl group/ethanol unit, affording the corresponding carboxylic acids in a selective manner.

Oxidation of primary aliphatic aldehydes with p- trifluoromethylphenyl(difluoro)-λ 3-bromane in dichloromethane at 0 °C afforded acid fluorides selectively in good yields, while that of aromatic aldehydes in chloroform at room temperature produced aryl difluoromethyl ethers. A larger migratory aptitude of aryl groups compared to primary alkyl groups during a 1,2-shift from carbon to an electron-deficient oxygen atom in bromane(III) Criegee-type intermediates will result in these differences in the reaction courses. © 2011 American Chemical Society.

We have designed a series of hydroxy(aryl)-(3)-iodane-[18]crown-6 complexes, prepared from the corresponding iodosylbenzene derivatives and superacids in the presence of [18]crown-6, and have investigated their reactivities in aqueous media. These activated iodosylbenzene monomers are all non-hygroscopic shelf-storable reagents, but they maintain high oxidizing ability in water. The complexes are effective for the oxidation of phenols, sulfides, olefins, silyl enol ethers, and alkyl(trifluoro)borates under mild conditions. Furthermore, hydroxy-(3)-iodane-[18]crown-6 complexes serve as efficient progenitors for the synthesis of diaryl-, vinyl-, and alkynyl-(3)-iodanes in water. Other less polar organic solvents, such as methanol, acetonitrile, and dichloromethane, are also usable in some cases.

Reduction of cis-N-triflylaziridines with 10 equiv of Red-Al in toluene at-40 to 0 °C selectively afforded corresponding deprotected parent aziridines in good to high yields. N,N-Dialkyltriflylamides were also successfully cleaved under similar reaction conditions. © 2012 American Chemical Society.

We have developed an efficient Rh-catalyzed (perfluoroalkyl)olefination reaction of acetanilides, which provides a versatile synthetic entry to a range of perfluoroalkylated compounds.

Bench-top-storable (Z)-enethiol reagents: gold (Z)-1-decenylthiolates were synthesized stereoselectively in high yields. They are stable upon storage at room temperature without protection from light, and react smoothly with various alkyl halides, α,β-unsaturated ketones, and electron-deficient aryl halides with excellent stereoselectivity.

Cross-coupling is a fundamental reaction in the synthesis of functional molecules, and has been widely applied, for example, to phenols, anilines, alcohols, amines and their derivatives. Here we report the Ni-catalysed Stille cross-coupling reaction of quaternary ammonium salts via C-N bond cleavage. Aryl/alkyl-trimethylammonium salts [Ar/R-NMe3](+) react smoothly with arylstannanes in 1: 1 molar ratio in the presence of a catalytic amount of commercially available Ni(cod)(2) and imidazole ligand together with 3.0 equivalents of CsF, affording the corresponding biaryl with broad functional group compatibility. The reaction pathway, including C-N bond cleavage step, is proposed based on the experimental and computational findings, as well as isolation and single-crystal X-ray diffraction analysis of Ni-containing intermediates. This reaction should be widely applicable for transformation of amines/quaternary ammonium salts into multi-aromatics.

In this review, we show that intermolecular hypervalent I(III)…O interactions play an essential role in the complexation of organo-λ3-iodanes with crown ethers. In addition to the well-known driving force for the complexation of crown ethers, ion-dipole interaction, and hydrogen bonding interaction, our result provides a new class of interaction in supramolecular chemistry of crown ethers. Both solid state structure analysis and solution chemistry indicate that diaryl-, 1-alkenyl(phenyl)-, 1-alkynyl(phenyl)-, and hydroxy(phenyl)-λ3-iodanes form stable complexes with 18-crown-6 through hypervalent I(III)…O interactions. The complexation not only increases the stability of these hypervalent λ3-iodanes but also holds its high reactivity toward nucleophiles. The complex of hydroxy(phenyl)-λ3-iodanes with 18-crown-6 serve as versatile oxidizing agents, especially in water.

Aliphatic phenylchloronium ylide with bis(trifluoromethylsulfonyl)methylidene group was synthesized. Thermal transylidation of 4-(trifluoromethyl)phenylbromonium his (trifluoromethylsulfonyl)methylide in chlorobenzene as a solvent at 130 degrees C afforded phenylchloronium bis(trifluoromethylsulfonyl)methylide in a moderate yield. Phenylbromonium and phenyliodonium ylides were also prepared by the thermal transylidation to bromo- and iodobenzenes. The reaction probably involves initial thermal generation of bissulfonylcarbene (Tf2C:), followed by nucleophilic attack of a halobenzene toward the electron-deficient carbene center. Solid-state structures of these aliphatic phenylhalonium ylides were lanalyzed and compared with each other. (C) 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:325-330, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20683

Ligand exchange of p-CF3C6H4BrF2 with acetoxy groups using AcOH and Ac2O affords (diacetoxybromo)benzene in a high yield, which undergoes azirldination of alkenes In the presence of TfNH2 and sulfamate esters in one pot under mild conditions. The azirldination with TfNH2 proceeds stereospecifically with retention of stereochemistry of olefins at room temperature using limiting amounts of olefins under transition-metal-free conditions. The one-pot aziridination procedure using sulfamate esters can be applied to the Intramolecular versions.

Hypervalent organo-λ3-iodanes have attracted great interest in organic synthesis; however, the chemistry of hypervalent organo-λ3-bromanes remains largely unexplored, mainly because of synthetic difficulties. Iodobenzene is readily oxidized by common oxidants such as peracids under mild conditions, whereas bromobenzene is inert. Since the ionization potential of bromobenzene (8.98 eV) is higher than that of iodobenzene (8.69 eV), hypervalent-λ3-bromane would show much higher reactivity. We overcame this problem by using difluoro(aryl)-λ3-bromane (Frohn's reagent), which serves as a pivotal progenitor of various λ3-bromanes including imino-λ3-bromane, cyclopent-1-enyl-λ3-bromane, (E)-β-alkylvinyl-λ3-bromane, and diacetoxy-λ3-bromane. These reagents possess highly unusual reactivity based on the enormously enhanced nucleofugality of the aryl-λ3-bromanyl group.

Fluorescent thiol-organosilica nanoparticles with 100 nm diameter (F-thiol-OS-100) were applied for time-lapse fluorescence imaging. The evaluation of F-thiol-OS-100 for quantitative analysis demonstrated great advantages as compared with quantum dots and organic fluorescent dye. Time-lapse fluorescence imaging of mouse peritoneal macrophages using F-thiol-OS-100 clearly demonstrated cellular uptake, and single cell analysis showed various patterns of uptake kinetics that could be quantitatively evaluated. We also performed quantitative analysis of endosomal uptake and movements in single cells. A correlation between morphologic findings and endosomal uptake and movement over time was also observed and analyzed quantitatively. The F-thiol-OS-100 showed high potential as a new fluorescence marker for time-lapse fluorescence imaging and quantitative single cell functional analysis for nanomedicine development. From the Clinical Editor: In this study the authors report on 100 nm thiol-organosilica nanoparticles as time-lapse flurescent markers. F-thiol-OS-100 proved to be superior to quantum dots and organic flurescent dyes, and enabled quantitative single cell functional analysis. © 2013 Elsevier Inc.

We report the first transition metal-free and trans-selective alkynylboration reaction of alkynes. This unprecedented carboboration reaction is enabled by pseudo-intramolecular activation of alkynylboronates using propargylic alcohols. The carboboration affords 4-alkynyl-1,2-oxaborol-2(5H)-ols, which are not only versatile building blocks but also exhibit strong violet-blue fluorescence emission.

Novel conditions for the transformation of gem-dibromomethylenes to ketones are described. gem-Dibromo compounds were treated with acetic anhydride and triethylamine in dichloromethane/water at room temperature under an air atmosphere to give the corresponding ketones in moderate yields. A radical mechanism is proposed based on experimental results.

We report herein, for the first time, the stereoselective synthesis of simple (E)-β-alkylvinyl(aryl)-λ3-bromanes via a boron-λ3-bromane exchange reaction and their unique bimolecular nucleophilic substitutions at the vinylic ipso carbon atom under mild conditions. Interestingly, even weakly nucleophilic anions such as conjugate bases of superacids (HBF4, TfOH, Tf2CH 2, Tf3CH, Tf2NH, etc.) function as nucleophiles toward the vinyl-λ3-bromanes. For instance, the vinylic SN2 reaction of (E)-vinyl-λ3-bromanes with potassium bis(triflyl)methanide stereoselectively produced (Z)-vinyloxy oxosulfonium ylides with exclusive inversion of configuration via oxygen attack, while that with potassium bis(triflyl)imide afforded predominantly (Z)-vinyloxysulfoximines. In marked contrast, (E)-β-alkylvinyl- λ3-iodanes do not undergo the vinylic SN2 reaction with these conjugate bases of superacids. The differences between the nucleofugalities of aryl-λ3-iodanyl and aryl- λ3-bromanyl groups (the latter being greater) probably play a pivotal role in these unique reactions. © 2011 American Chemical Society.