Rhodium(III)-Catalyzed B(4)-Azo Coupling of -Carboranes with Aryl Diazonium Tetrafluoroborates.

Rh(III)-catalyzed B(4)-azo coupling reactions of -carborane acids with aryl diazonium tetrafluoroborates have been developed, leading to the regioselective formation of B(4)-azo-coupled -carboranes. Moreover, B(4)-azo-coupled -carboranes can be further functionalized by introducing a second azo group, producing B(4)-C(1)-di(arylazo) -carborane. The B(4)-azo group as an efficient directing group enables catalytic C-H amidation reactions, providing a new synthetic route for complex -carborane derivatives.

Selective ring expansion and C-H functionalization of azulenes.

We report a transition metal-catalyzed ring expansion of azulene that can be contrasted with C-H functionalization. This study represents the first example of the successful ring expansion of azulene using Cu(hfacac) (hfacac: hexafluoroacetylacetonate) with a diazo reagent. This result is notable for extending the Buchner reaction, previously limited to benzenoid aromatics, to nonbenzenoid compounds.

Iridium-Catalyzed Regioselective B(4)-Alkenylation and B(3,5)-Dialkenylation of -Carboranes.

Iridium(I)-catalyzed regioselective B(4)-alkenylation has been developed from -carboranyl sulfoxonium ylides and alkynes through B(4)-H activation. The sequential B(4)- and B(6)-alkenylation afforded B(3,5)-dialkenylated -carboranyl sulfoxonium ylides in one pot. Eventually, two alkenyl groups, the same or different, were introduced at positions 3 and 5 of the carborane.

Iridium(III)-Catalyzed Regioselective B(4)-H Amination of -Carboranes with Sufilimines.

Iridium(III)-catalyzed regioselective B(4)-H amination is developed from the reaction of -carborane acids with sulfilimines without any oxidants under mild conditions, which leads to a wide range of B(4)-H aminated -carboranes in good yields with a broad substrate scope. Moreover, the selective B(3,6)-diamination reaction of the -carborane acid was achieved. The present reaction is attractive from a practical point of view because dibenzothiophene is quantitatively recovered and reused.

Iridium(III)-Catalyzed C-H Cyclization of Sulfoximines with Diazo Meldrum's Acids for the Synthesis of Cyclic Sulfoximines.

Iridium(III)-catalyzed C-H cyclization of sulfoximines with diazo Meldrum's acid provided cyclic sulfoximines with a carbonyl group in good to excellent yields. These compounds were easily converted into unsubstituted and arylated sulfoximines. Moreover, the vinyl triflates obtained from the cyclic sulfoximines underwent palladium(II)-catalyzed cross-coupling reactions with a variety of aryl, arylalkynyl, and heteroatom (N and S) nucleophiles, affording a wide range of monosubstituted sulfoximines in high yields.

Regiodivergent metal-catalyzed B(4)- and C(1)-selenylation of -carboranes.

Regiodivergent transition metal-catalyzed B(4)- and C(1)-selenylation reactions of -carboranes have been demonstrated. Namely, Ru(ii)-catalysis selectively generated B(4)-selenylated -carboranes from the reaction of -carborane acids with arylselenyl bromides with the release of carbon dioxide. In contrast, Pd(ii) catalysis provided exclusively C(1)-selenylated -carboranes from the decarboxylative reaction of -carborane acids with diaryl diselenides.

Synthesis of -Carborane-Fused Pyrazoles through Sequential C-N Bond Formation.

Transition-metal-free synthetic method for -carborane-fused pyrazoles as a new scaffold has been developed from the reaction of B(4)-acylmethyl or B(3,5)-diacylmethyl -carborane with 2-azido-1,3-dimethylimidazolinium hexafluorophosphate (ADMP) in the presence of DBU in acetonitrile through sequential diazotization and cyclization reaction in one pot, consequently allowing twofold C-N bond formation under extremely mild conditions and high functional group tolerance.

Iridium(III)-Catalyzed Regioselective B(4)-H Allenylation of -Carboranes by Ball Milling.

We disclose an iridium(III)-catalyzed regioselective B(4)-H allenylation of -carboranes from -carborane acids and propargyl carbonates under ball-milling conditions. This study sheds light on a novel method to accomplish regioselective B(4)-allenylation of -carborane that cannot be realized through conventional solution-based reactions. Control experiments, including solution, neat, microwave, and high-temperature reactions, reveal that the B(4)-H allenylation of -carborane is unique for ball-milling conditions.

Iridium(III)-Catalyzed B(4)-Acylmethylation and B(3,5)-Diacylmethylation from -Carboranes and Sulfoxonium Ylides.

An iridium(III)-catalyzed regioselective acylmethylation of the cage B(4)-H bond in -carborane acids with sulfoxonium ylides is demonstrated through B(4)-H activation in ethanol under very mild conditions, affording a number of B(4)-acylmethylated -carboranes. Additionally, the selective sequential B(4)- and B(6)-acylmethylation reactions finally gave B(3,5)-diacylmethylated -carboranes in one pot.

Rhodium-Catalyzed B(4)-H and B(3)-H Alkylation Reaction of Pyridyl -Carboranes with α-Diazodicarboxylates.

An efficient Rh-catalyzed B(4)-H and B(3)-H alkylation reaction was demonstrated from the reactions of a variety of pyridyl -carboranes with α-diazodicarboxylates with the release of molecular nitrogen, leading to the production of B(4)-H and B(3)-H alkylated -carboranes in good to excellent yields with high selectivity, a wide substrate scope, and good functional group tolerance.

Mechanochemical Iridium(III)-Catalyzed B-Amidation of -Carboranes with Dioxazolones.

Mechanochemistry was successfully applied to the functionalization of carboranes. The mechanochemical iridium(III)-catalyzed regioselective B(3)- and B(4)-amidation of unsubstituted -carboranes with dioxazolones was developed. In addition, the mechanochemical iridium(III)-catalyzed regioselective B(4)-amidation of substituted -carboranes was demonstrated.

Direct and Regioselective Palladium(II)-Catalyzed B(4)-H Monoacyloxylation and B(4,5)-H Diacetoxylation of -Carborane Acids with Phenyliodonium Dicarboxylates.

A direct B(4)-H monoacyloxylation via a Pd-catalyzed regioselective B(4)-H activation of -carborane acids with phenyliodonium dicarboxylates was developed, and a series of B(4)-H monoacyloxylated -carboranes decorated with active groups were synthesized with moderate to good yields as well as excellent selectivity. In addition, a direct B(4,5)-H diacetoxylation from -carborane acids with phenyliodonium diacetate was demonstrated.

Rhodium(III)-Catalyzed Sequential C-H Activation and Cyclization from N-Methoxyarylamides and 3-Diazooxindoles for the Synthesis of Isochromenoindolones.

An efficient synthetic method for structurally various isochromenoindolones has been demonstrated through Rh(III)-catalyzed C-H activation followed by a cyclization reaction of N-methoxyarylamides with 3-diazooxindoles. The sequential reaction involves the streamlined formation of C-C and C-O bonds in one pot. The present method provides a broad range of isochromenoindolones as a new privileged scaffold in moderate to good yields with the release of methoxyamine and molecular nitrogen and has the benefits of a broad substrate scope and good functional group tolerance.

Selective B(5,8,9)-Triarylation Reaction of -Carboranes through Determination of the Order of Introduction of Aryl Groups into B(4)-Acylamino--carboranes.

Palladium-catalyzed iterative cage B-H arylation reaction of a wide range of B(4)-acylamino--carboranes with aryl iodides has been developed, leading to the formation of B(5,8,9)-triarylated B(4)-acylamino--carboranes with excellent regioselectivity. Moreover, B(5,8,9)-triarylated carboranes bearing three different aryl groups were synthesized from B(4)-acylamino--carborane and three different aryl iodides. The order of introduction [B(9) > B(8) > B(5)] of aryl groups into the B(5,8,9)-triarylation reaction was determined for the first time through NMR monitoring and X-ray analyses.

Iridium-Catalyzed Cage B(4)-Amidation Reaction of -Carboranes with Dioxazolones: Selective Synthesis of Amidated -Carboranes and Amidated and Methoxycarbonylated -Carboranes.

Described is the Ir-catalyzed cage B(4)-amidation of -carboranes with dioxazolones by carboxylic acid-assisted B(4)-H bond activation under extremely mild conditions, affording amidated -carboranes and amidated and methoxycarbonylated -carboranes through sequential B(4)-amidation, O-methylation, and B(3)-deboronation in one pot. Carboxylic acid used as a directing group after the cage B(4)-amidation is efficiently trapped by trimethylsilyldiazomethane instead of undergoing decarboxylation. Mechanism studies demonstrated that the O-methylation through trapping of acid occurred first, followed by the B(3)-deboronation.

Iridium(III)-Catalyzed Sequential C(2)-Arylation and Intramolecular C-O Bond Formation from Azulenecarboxylic Acids and Diaryliodonium Salts Access to Azulenofuranones.

Described herein is the iridium-catalyzed sequential C(2)-arylation reaction and intramolecular C-O bond formation from azulenecarboxylic acids and diaryliodonium salts, leading to the formation of 3-arylazulenofuranones. The sequential reaction proceeded smoothly through generation of 2-arylazulene-1-carboxylic acids derived from the iridium-catalyzed regioselective C(2)-arylation reaction without the decarboxylation reaction.

Sequential 1,3-- to - and 1,3-- to -Migration of Sulfonyl Groups through the Synthesis of 1,4-Diazepines from the Aza-[5 + 2] Cycloaddition of Indoloazomethine Ylides.

Described herein is the sequential 1,3-- to - and 1,3-- to -migration of sulfonyl groups through the synthesis of 1,4-diazepines from an operationally simple thermal aza-[5 + 2] cycloaddition reaction of indoloazomethine ylides with dialkyl acetylenedicarboxylates under mild conditions, leading to the formation of -sulfonylated 1,4-diazepines.

Iridium-Catalyzed Cyclative Indenylation and Dienylation through Sequential B(4)-C Bond Formation, Cyclization, and Elimination from -Carboranes and Propargyl Alcohols.

Described herein is the first iridium-catalyzed cyclative indenylation through sequential B(4)-C and intramolecular C-C bond formation from -carboranes and propargyl alcohols, leading to the formation of B(4)-indenylated -carboranes with excellent regioselectivity via direct B-H activation. Moreover, the iridium-catalyzed regioselective 1,3-dienylation has been accessed through sequential B-H activation, dehydration, and decarboxylation, producing B(4)-dienylated -carboranes.

Expansion of Azulenes as Nonbenzenoid Aromatic Compounds for C-H Activation: Rhodium- and Iridium-Catalyzed Oxidative Cyclization of Azulene Carboxylic Acids with Alkynes for the Synthesis of Azulenolactones and Benzoazulenes.

Rhodium-catalyzed oxidative [4 + 2] cyclization reactions through the C-H activation of azulene carboxylic acids as nonbenzenoid aromatic compounds with symmetrical and unsymmetrical alkynes were developed under aerobic conditions, which produced azulenolactone derivatives with a wide substrate scope and excellent functional group tolerance. Interestingly, azulenic acids in reaction with alkynes underwent iridium-catalyzed [2 + 2 + 2] cyclization accompanied by decarboxylation to afford tetra(aryl)-substituted benzoazulene derivatives. The reactivity order for C-H activation reaction is greater toward azulene-6-carboxylic acid, azulene-1-carboxylic acid, and azulene-2-carboxylic acid.

Selective C-C bond formation from rhodium-catalyzed C-H activation reaction of 2-arylpyridines with 3-aryl-2-azirines.

A novel method for the synthesis of acylmethyl-substituted 2-arylpyridine derivatives using 3-aryl-2-azirines was developed by exploring a prototype reaction using DFT-calculations and carrying out targeted experiments guided by the calculated mechanism. 2-Azirine was initially hypothesized to ring-open at the metal center to furnish familiar metal nitrene complexes that may undergo C-N coupling. Computational studies quickly revealed and prototype experimental work confirmed that neither the formation of the expected metal nitrene complexes nor the C-N coupling were viable.

Pyrazinoindole-Based Lewis-Acid/Base Assembly: Intriguing Intramolecular Charge-Transfer Switching through the Dual-Sensing of Fluoride and Acid.

Pyrazinoindole-based Lewis-acid/base assemblies are prepared through the use of regioselective formal [3 + 3] cycloaddition reactions, and their intriguing photophysical properties are described. The assemblies exhibit strong emissions in THF solution, which are attributed to through-space intramolecular charge-transfer (ICT) transitions between the branched Lewis-acid/base moieties. Furthermore, these show ratiometric color-change responses in PL titration experiments, which give rise to new colors through turn-on emissions ascribable to ICT transitions that alternate between the pyrazinoindole units and each triarylboryl or amino moiety, a consequence of the binding of the fluoride or acid.

Synthesis of Diaryl Ketones through Oxidative Cleavage of the C-C Double Bonds in N-Sulfonyl Enamides.

An oxidative cleavage of a C-C double bond is developed from the photochemical [2+2]-cycloaddition of diaryl N-tosyl enamides, aryl heteroaryl N-tosyl enamides, and N-tosyl cyclic enamides with singlet molecular oxygen, followed by a ring-opening reaction mediated by CsCO under air and sunlight without the use of photosesitizer, producing symmetrical and unsymmetrical diaryl, heterodiaryl, and cyclic ketones in good to excellent yields. Moreover, the oxidative cleavage of C-C triple bonds from 1-alkynes is demonstrated for the synthesis of symmetrical and unsymmetrical ketones from the Cu-catalyzed [3+2]-cycloaddition, Rh-catalyzed alkoxyarylation, photooxygenation, and ring-opening reaction in one-pot. Because the synthesis of the symmetrical and unsymmetrical diaryl and/or heterodiaryl ketones bearing an electron-donating group is not easy, the present method is notable.

Regioselective Synthesis of Indolopyrazines through a Sequential Rhodium-Catalyzed Formal [3+3] Cycloaddition and Aromatization Reaction of Diazoindolinimines with Azirines.

A regioselective synthetic method for the preparation of indolopyrazines was demonstrated through a sequential Rh-catalyzed formal [3+3] cycloaddition and aromatization reaction of a wide range of diazoindolinimines with azirines. Because the previously reported synthetic methods afforded mixtures of indolopyrazines, the present method using unsymmetrical azirines has a strong advantage from a regioselectivity viewpoint.

Trichloroethylene and Parkinson's Disease: Risk Assessment.

This study was conducted to investigate the mechanism of action and extent of selective dopaminergic neurodegeneration caused by exposure to trichloroethylene (TCE) leading to the endogenous formation of the neurotoxin 1-trichloromethyl-1,2,3,4-tetrahydro-β-carboline (TaClo) in rodents. Beginning at 3 months of age, male C57BL/6 mice received oral TCE dissolved in vehicle for 8 months. Dopaminergic neuronal loss was assessed by nigral tyrosine hydroxylase (TH) immunoreactivity.