Benchtop-Stable Hypervalent Bromine(III) Compounds: Versatile Strategy and Platform for Air- and Moisture-Stable λ3-Bromanes.

We present the first synthesis of air/moisture-stable λ3-bromanes (9 and 10) by using a cyclic 1,2-benzbromoxol-3-one (BBX) strategy. X-ray crystallography and NMR and IR spectroscopy of N-triflylimino-λ3-bromane (12) revealed that the bromine(III) center is effectively stabilized by intramolecular R-Br-O hypervalent bonding. This strategy enables the synthesis of a variety of air-, moisture-, and benchtop-stable Br-hydroxy, -acetoxy, -alkynyl, -aryl, and bis[(trifluoromethyl)sulfonyl]methylide λ3-bromane derivatives.

A versatile iodo(III)etherification of terminal ethynylsilanes using BF3-OiPr2 and alkyl benzyl ethers.

A series of (E)-α-silyl-ß-alkoxyvinyl-λ3-iodanes was synthesized from iodosylbenzene, BF3-ether complexes, and terminal ethynylsilanes. The combined use of BF3-OiPr2 and benzyl ethers of primary alcohols (ROBn) allows the chemoselective transfer of primary alkoxy groups (RO) onto the ß-position of the terminal ethynylsilanes.

Room-temperature chemical synthesis of C2.

Diatomic carbon (C2) is historically an elusive chemical species. It has long been believed that the generation of C2 requires extremely high physical energy, such as an electric carbon arc or multiple photon excitation, and so it has been the general consensus that the inherent nature of C2 in the ground state is experimentally inaccessible. Here, we present the chemical synthesis of C2 from a hypervalent alkynyl-λ3-iodane in a flask at room temperature or below, providing experimental evidence to support theoretical predictions that C2 has a singlet biradical character with a quadruple bond, thus settling a long-standing controversy between experimental and theoretical chemists, and that C2 serves as a molecular element in the bottom-up chemical synthesis of nanocarbons such as graphite, carbon nanotubes, and C60.

Mechanistic Study on Aryl-Exchange Reaction of Diaryl-λ3-iodane with Aryl Iodide.

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.

Mechanistic Studies on the Generation and Properties of Superelectrophilic Singlet Carbenes from Bis(perfluoroalkanesulfonyl)bromonium Ylides.

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.

Stereoselective synthesis and reaction of gold(I) (Z)-enethiolates.

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,ß-unsaturated ketones, and electron-deficient aryl halides with excellent stereoselectivity.

Metal-free C-H amination of unactivated hydrocarbons with sulfonylimino-λ(3)-bromanes generated in situ from (diacetoxybromo)benzene.

A simple method for direct metal-free C-H amination of unactivated hydrocarbons using easy-handling diacetoxy-λ(3)-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-λ(3)-bromane.

Reactivity of hydroxy- and aquo(hydroxy)-λ3-iodane-crown ether complexes.

We have designed a series of hydroxy(aryl)-λ(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-λ(3)-iodane-[18]crown-6 complexes serve as efficient progenitors for the synthesis of diaryl-, vinyl-, and alkynyl-λ(3)-iodanes in water. Other less polar organic solvents, such as methanol, acetonitrile, and dichloromethane, are also usable in some cases.

Time-lapse fluorescence imaging and quantitative single cell and endosomal analysis of peritoneal macrophages using fluorescent organosilica nanoparticles.

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.

Metal-free α-CH amination of ethers with hypervalent sulfonylimino-λ3-bromane that acts as an active nitrenoid.

Hypervalent N-triflylimino-λ(3)-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.

A catalytic version of hypervalent aryl-λ3-iodane-induced Hofmann rearrangement of primary carboxamides: iodobenzene as an organocatalyst and m-chloroperbenzoic acid as a terminal oxidant.

The first catalytic version of hypervalent aryl-λ(3)-iodane-induced Hofmann rearrangement of primary carboxamides, which probably involves in situ generation of a tetracoordinated bis(aqua)(hydroxy)phenyl-λ(3)-iodane complex as an active oxidant from a catalytic amount of iodobenzene by the reaction with m-chloroperbenzoic acid in the presence of HBF(4) in dichloromethane-water under mild conditions, was developed.

Synthesis and structure of hypervalent diacetoxybromobenzene and aziridination of olefins with imino-λ3-bromane generated in situ under metal-free conditions.

Ligand exchange of p-CF(3)C(6)H(4)BrF(2) with acetoxy groups using AcOH and Ac(2)O affords (diacetoxybromo)benzene in a high yield, which undergoes aziridination of alkenes in the presence of TfNH(2) and sulfamate esters in one pot under mild conditions. The aziridination with TfNH(2) 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.

Oxidation of primary aliphatic and aromatic aldehydes with difluoro(aryl)-λ3-bromane.

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.

Highly regioselective amination of unactivated alkanes by hypervalent sulfonylimino-λ³-bromane.

Amination of alkanes has generally required metal catalysts and/or high temperatures. Here we report that simple exposure of a broad range of alkanes to N-triflylimino-λ(3)-bromane 1 at ambient temperature results in C-H insertion of the nitrogen functionality to afford triflyl-substituted amines in moderate to high yields. Marked selectivity for tertiary over secondary C-H bonds was observed; primary (methyl) C-H bonds were inert. Addition of hexafluoroisopropanol to inhibit decomposition of 1 dramatically improved the C-H amination efficiencies. Second-order kinetics, activation parameters (negative activation entropy), deuterium isotope effects, and theoretical calculations suggest a concerted asynchronous bimolecular transition state for the metal-free C-H amination event.

Hypervalent phenyl-λ3-iodane-mediated para-selective aromatic fluorination of 3-phenylpropyl ethers.

Exposure of 3-phenylpropyl ethers to an activated iodosylbenzene monomer·18-crown-6 complex [PhI(OH)BF(4)·18C6] in the presence of BF(3)-Et(2)O and water results in the para-selective monofluorination of benzene ring via neighboring alkoxy group participation and directly affords 3-(4-fluorophenyl)propyl ethers regioselectively in good yields.

Weakly nucleophilic conjugate bases of superacids as powerful nucleophiles in vinylic bimolecular nucleophilic substitutions of simple ß-alkylvinyl(aryl)-λ3-bromanes.

We report herein, for the first time, the stereoselective synthesis of simple (E)-ß-alkylvinyl(aryl)-λ(3)-bromanes via a boron-λ(3)-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 (HBF(4), TfOH, Tf(2)CH(2), Tf(3)CH, Tf(2)NH, etc.) function as nucleophiles toward the vinyl-λ(3)-bromanes. For instance, the vinylic S(N)2 reaction of (E)-vinyl-λ(3)-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)-ß-alkylvinyl-λ(3)-iodanes do not undergo the vinylic S(N)2 reaction with these conjugate bases of superacids. The differences between the nucleofugalities of aryl-λ(3)-iodanyl and aryl-λ(3)-bromanyl groups (the latter being greater) probably play a pivotal role in these unique reactions.

Imination of sulfides and sulfoxides with sulfonylimino-lambda3-bromane under mild, metal-free conditions.

Exposure of sulfides and sulfoxides to trifluoromethanesulfonylimino(aryl)-lambda(3)-bromane in dichloromethane at 0 degrees C results in a facile transfer of the sulfonylimino group to sulfur atoms and affords N-triflylsulfilimines and -sulfoximines in high yields under transition-metal-free conditions. Imination of (R)-methyl p-tolyl sulfoxide proceeded with predominant retention of configuration at the stereogenic sulfur center. The Hammett plot afforded rho values of -0.58 for para-substituted thioanisoles and -0.49 for their equivalent sulfoxides, which suggests a buildup of positive charge on the sulfur atoms of sulfides and sulfoxides in the transition state. Calculations suggest a bimolecular nucleophilic-substitution mechanism on the negatively charged nitrogen atom of the sulfonylimino-lambda(3)-bromane, which involves the attack of a sulfide from the opposite side to bromine(III).

Hypervalent lambda3-bromane strategy for Baeyer-Villiger oxidation: selective transformation of primary aliphatic and aromatic aldehydes to formates, which is missing in the classical Baeyer-Villiger oxidation.

A conceptually distinct, modern strategy for Baeyer-Villiger oxidation (BVO) was developed. Our novel method involves initial hydration of water to carbonyl compounds, followed by ligand exchange of hypervalent aryl-lambda(3)-bromane on bromane(III) with the resulting hydrate, yielding a new type of activated Criegee intermediate. The intermediate undergoes BV rearrangement and produces an ester via facile reductive elimination of an aryl-lambda(3)-bromanyl group, because of the hypernucleofugality. The novel strategy makes it possible to induce selectively the BV rearrangement of straight chain primary aliphatic as well as aromatic aldehydes, which is missing in the classical BVO: for instance, octanal and benzaldehyde afforded rearranged formate esters with high selectivity (>95%) under our conditions, while the attempted classical BVO produced only carboxylic acids. This firmly establishes the powerful nature of new methodology for BVO.

Hypervalent N-sulfonylimino-lambda(3)-bromane: active nitrenoid species at ambient temperature under metal-free conditions.

The synthesis and reactions of N-triflylimino-lambda(3)-bromane are summarized. The hypervalent iminobromane functions as a highly active nitrenoid species at ambient temperature under transition metal-free conditions, probably because of the increased hypernucleofugality of aryl-lambda(3)-bromanyl groups compared to that of aryl-lambda(3)-iodanyl groups. The imino-lambda(3)-bromane undergoes stereospecific aziridination of olefins and transylidation to aromatic nitrogen heterocycles, trialkylamines and iodobenzenes. Difluoro-lambda(3)-bromane-induced Hofmann rearrangement of primary arylsulfonamides is also discussed.