Site-Selective Aerobic C-H Monoacylation of Carbazoles Using Palladium Catalysis.

This manuscript describes the development of a remarkably general palladium-catalyzed monoacylation of carbazoles using toluene derivatives playing the dual role of acyl source and organic solvent. The method uses NHPI as the cocatalyst and oxygen as the sole oxidant. Interestingly, the acylation of monosubstituted N-pyridylcarbazoles takes place regioselectively at the C-8 position. The scope of the method is explored using aldehyde as the acyl source. This highly site-selective acylation proceeds through a radical process.

New classes of carborane-appended 5-thio-D-glucopyranose derivatives.

A series of carborane-appended 5-thio-D-glucopyranose (5-TDGP) derivatives containing one to two 5-TDGP moieties were synthesized via click cycloaddition reaction as well as following the traditional methods. Among the carboranyl-5-TDGP derivatives, the decapitated nido-carboranyl derivative 18 was found to be highly water-soluble and therefore its preliminary biodistribution study was conducted. A comparative biological evaluation of 18 versus its carboranyl-D-glucopyranose analog 19 with human hepatocellular carcinoma cells (SK-Hep1) indicated 5-TDGP to be a better boron carrier than normal D-glucopyranose. The carboranyl-5-TDGP 18 showed a nearly two fold increase in cellular boron accumulation than carboranyl-D-glucopyranose analog 19 over a period of 2 h. The accumulation of both 18 and 19 was found to occur in a temperature dependent manner. The higher accumulation of 18 suggested excellent promise for it to be a candidate for further evaluation as a future BNCT agent.

Enhanced π-conjugation and emission via icosahedral carboranes: synthetic and spectroscopic investigation.

The ability of ortho-, meta- and para-carboranes to enhance the emission intensity has been compared. For this purpose a series of carborane-appended 1,3,5-triphenylbenzene (TB) and 1,3,5- tris(biphenyl-4-yl)benzene (TBB) containing three ortho-, meta- and para-carborane clusters directly attached to the conjugated cores have been synthesized employing Suzuki, Heck, and trimerization reactions. The incorporation of the icosahedral carboranes was associated with a red shift in the UV absorption spectrum of up to 13 nm as well as enhancements of the emission intensities of up to 154%. The presence of ortho-carboranes showed the maximum red shift in the UV spectrum whereas the maximum enhancement of the emission intensity was observed in the presence of meta-carborane clusters. The order of π-conjugation extension is found to be ortho > meta ≈ para. A comparative thermal analysis indicated o-carborane-appended trimers to be the most thermally stable in the series. Proton NMR spectra of reported carborane-appended trimers indicated that ortho- and meta-carborane cages have benzenelike characteristics.

Carboranylpyrroles: a synthetic investigation.

The unusual reactivity of carborane mono- and dialdehydes with pyrroles in the presence of acid catalysts leads to the formation of a new class of carboranyl mono- and dipyrro derivatives.

"Click" synthesis and properties of carborane-appended large dendrimers.

Large dendrimers, noted G(n)-3(n+2)cage, containing 3(n+2) o-carborane cluster cages MeC(2)B(10)H(10) at their peripheries (n = number of generation noted G(n)) have been synthesized by Huisgen-type azide alkyne Cu(I)-catalyzed dipolar "click" cycloaddition reactions (CuAAC) between an o-carborane monomeric cluster containing an ethynyl group and arene-centered azido-terminated dendrimers G(n)-3(n+2)N(3) of generations 0, 1, and 2. Attempts to synthesize higher-generation dendrimers of this family yielded insoluble materials. The carborane dendrimers G(0)-9cage, G(1)-27cage, and G(2)-81cage have been characterized by (1)H, (13)C, (11)B NMR, elemental analysis, matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectroscopy, and size exclusion chromatography (SEC) showing low polydispersities, dynamic light scattering (DLS) showing hydrodynamic diameters of 5.7 nm for the G(1)-27cage and the 12.9 nm for the G(2)-81cage. These dendrimers are extremely robust thermally, with 10% mass loss temperatures of 411 °C for the G(0)-9cage, 371 °C for the G(1)-27cage, and 392 °C for the G(2)-81cage. They all showed a strong absorption in the UV region peaking at 258 nm, whereas emission spectra of low intensities were observed between 280 and 480 nm.

Advances in the metallacarborane chemistry of f-block elements.

The role of carborane clusters in organometallic chemistry is diverse. A number of carborane cage systems such as C(2)B(4), C(2)B(9) and C(2)B(10) clusters have been extensively used for the synthesis of numerous metallacarboranes of s, p, d and f-block elements. An introduction to the chemistry of metallacarboranes is provided with an emphasis on the recent advances on the metallacarboranes of f-block elements.

Synthesis and properties of carborane-appended C(3)-symmetrical extended pi systems.

A series of C(3)-symmetric pi-conjugated compounds containing three to six o-carborane clusters have been synthesized by employing palladium-catalyzed Suzuki coupling reactions and palladium-catalyzed acetylation reactions, followed by silicon tetrachloride mediated trimerization reactions. Carborane-containing extended trimers were found to emit blue light. Incorporation of o-carborane clusters into extended pi-conjugated systems led to 22-70% enhancement of their relative fluorescence quantum yields. Decapitation of o-carborane clusters made these extended trimers water soluble, and their aqueous solutions were also found to be fluorescent, but with a reduced fluorescence intensity. The carborane-appended pi-conjugated compounds are found to be extremely thermally stable, and for some of these compounds only 10% mass loss occurred at temperatures close to 500 degrees C. The DSC thermograms of smaller C(cage)-appended trimers indicate the occurrence of solid-solid phase transitions.

Synthesis of a new class of carborane-containing star-shaped molecules via silicon tetrachloride promoted cyclotrimerization reactions.

Symmetrical star-shaped molecules with carborane clusters on the periphery have been synthesized in good yields via silicon tetrachloride mediated cyclotrimerization reactions of 9-benzyl derivatives of carboranes with acetyl group substitution on the benzene ring. Facile functionalization of these symmetrical core structures with 1-iodoheptane and trivinylchlorosilane produce compounds which could be used as liquid crystalline substances and precursors for synthesis of higher order carbosilane dendrons.

Electrochemical denitrificaton of simulated ground water.

Electrochemical denitrification of ground water was studied with an objective to maximize nitrate transformation to nitrogen gas. Aluminum, graphite, iron and titanium were selected as electrode materials. While aluminum, iron and titanium electrodes showed 70-97% nitrate reduction, with graphite electrode the removal was only 8%. Nitrate was transformed to ammonia with iron and aluminum electrodes but with titanium electrodes nitrogen was apparently the major end product. Iron electrodes exhibited the maximum reducing condition (ORP=-463mV) and titanium showed the minimum (ORP=-206mV). Nitrate reduction with titanium electrodes was retarded in the presence of chloride ions possibly due to formation of hypochlorite ions. The first-order nitrate transformation rate constant with respect to time decreased with decrease in current density. However, when the rate constant was expressed with respect to charge passed (Coulomb/l) it was nearly same under different experimental conditions (current density and pH). The study indicates that the process might be suitable for denitrification of drinking water.