Novel methodologies for the synthesis of functionalized lipophilic carboranes

Novel synthetic protocols for the synthesis of lipophilic carboranes were developed utilizing two C? C bond forming reactions, namely Baylis–Hillman and enynedioate cycloaddition reactions. Some of these carboranes were converted into further functionalized carboranes via nucleophilic allylic isomerization. Copyright © 2009 John Wiley & Sons, Ltd.     

Photoarylation of Iodocarboranes with Unactivated (Hetero)Arenes: Facile Synthesis of 1,2‐[(Hetero)Aryl]n‐o‐Carboranes (n=1,2) and o‐Carborane‐Fused Cyclics

Photoarylation of iodocarboranes with unactivated arenes/heteroarenes at room temperature has been achieved, for the first time, thus leading to the facile synthesis of a large variety of cage carbon mono(hetero)arylated and di(hetero)arylated o‐carboranes. This work represents a clean, efficient, transition‐metal‐free, and cheap synthesis of functionalized carboranes, which has significant advantages over the known methods.     

Carboranes as a Tool to Tune Phosphorescence

Phosphorescent transition‐metal complexes (PTMCs) have attracted great interest because of their excellent properties which may lead to promising applications in optoelectronics. In recent years, carboranes have been demonstrated to be a novel and effective tool to tune phosphorescence of PTMCs. This Concept article deals with the advances of carborane‐functionalized PTMCs for potential optical applications. The discussions are focused on the design strategies and synthetic procedures leading to carborane‐functionalized PTMCs, the influence of carboranes on the optical properties of PTMCs, and the promising optical applications of this interesting class of phosphorescent materials.     

Carborane functionalized pyrroles and porphyrins via the Suzuki cross-coupling reaction

A new route to carboranylated pyrroles and porphyrins is reported which involves the Suzuki coupling of readily available bromo- and boronic acid-pyrroles and bromoporphyrins with functionalized carboranes; the X-ray structures of two targeted products are presented and discussed.     

Photoarylation of Iodocarboranes with Unactivated (Hetero)Arenes: Facile Synthesis of 1,2-[(Hetero)Aryl]n-o-Carboranes (n=1,2) and o-Carborane-Fused Cyclics

Photoarylation of iodocarboranes with unactivated arenes/heteroarenes at room temperature has been achieved, for the first time, thus leading to the facile synthesis of a large variety of cage carbon mono(hetero)arylated and di(hetero)arylated o-carboranes. This work represents a clean, efficient, transition-metal-free, and cheap synthesis of functionalized carboranes, which has significant advantages over the known methods.     

Synthesis of functionalized carboranes as potential anticancer and BNCT agents

Carboranyl aldehydes react with alpha,beta-unsaturated esters, ketones, and nitriles in the presence of DABCO to provide functionalized carboranyl alcohols in good yields. Acetates of these alcohols undergo a facile isomerization with a variety of nucleophiles and afford structurally interesting carboranes. Biological evaluation of these molecules exhibited impressive antiproliferative activity for brain and breast cancer cells.     

Microwave-assisted synthesis of 3,1,2- and 2,1,8-Re(I) and 99mTc(I)-metallocarborane complexes

Microwave heating was used to prepare eta5-rhenium carborane complexes in aqueous reaction media. For carboranes bearing sterically demanding substituents, isomerization of the cage from 3,1,2 to 2,1,8 derivatives occurred concomitantly with complexation. Microwave heating was equally effective at the tracer level using technetium-99m, affording access to a new class of synthons for designing novel molecular imaging agents.     

Regioselective insertion of carborynes into ethereal C-H bond: facile synthesis of α-carboranylated ethers

Carborynes can exist in two resonance forms, bonding form vs biradical form. The biradical form can be readily generated via the elimination of LiI from 1-iodo-n-lithio-1,n-C(2)B(10)H(10) (n = 2, 7) under UV irradiation. They can undergo α-C-H bond insertion with aliphatic ethers, affording α-carboranylated ethers in excellent regioselectivity at room temperature. This serves as a new methodology for the generation of a series of functionalized carboranes bearing alkoxy units.     

Some aspects of the chemical behavior of icosahedral carboranes

Abatract  Important features of the chemical behavior of icosahedral carboranes are considered. The ways of introducing functional groups at the carbon and boron atoms of carboranes by conventional methods of organic chemistry and methods applicable only to carboranes are discussed. The latter methods include transformations of dicarbadodecaborate(14) dianions. Examples of the enantiomeric resolution of optically active carboranes, whose chirality is associated with the molecular asymmetry, are given. The diversity of chemical transformations of carboranes is exemplified by intramolecular nucleophilic rearrangements, cross-coupling reactions, and the formation of chelate metallacycles. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 801–822, April, 2008.     

实时直接分析高分辨质谱技术研究碳硼烷类化合物

该文运用高分辨质谱技术对实时直接分析(Direct analysis in real time,DART)离子化条件下碳硼烷化合物的质谱行为进行了研究,对碳硼烷化合物DART高分辨质谱中所得到的同位素峰簇进行了表征与归属。研究结果表明,选取的碳硼烷化合物在DART负离子条件下均能得到较好的质谱信号,这可能与硼笼结构的“缺电性”有关。含10个B原子的碳硼烷化合物形成的离子同位素峰簇信号中,通常情况下相对丰度最高的同位素峰中含2个10B以及8个11B。将碳硼烷化合物高分辨质谱分析的精确m/z数据信息与图谱中同位素峰轮廓分析相结合,是碳硼烷化合物有效的质谱定性分析与表征策略。     

Reaction of o‐Carboryne with Furans: Facile Synthesis of Carborane‐ Fused Oxanorbornenes and Their Derivatives

o‐Carboryne (1,2‐dehydro‐o‐carborane) is a very useful synthon for the synthesis of a variety of carborane‐functionalized molecules. Diels‐Alder reaction of o‐carboryne with furans gave a series of carborane‐fused oxanorbornenes in moderate to high yields using 1‐OTf‐1,2‐C₂B₁₀H₁₁ as carboryne precursor. The resultant cycloadducts can undergo hydrogenation, cyclic oxidation, bromination, [4 + 2]/[2 + 2] cycloaddition and nucleophilic ring opening reaction to afford a variety of highly functionalized carboranes that may find applications as useful basic units in medicine and materials science.     

Carboxylation reaction of a highly functionalized vinylic anion: a case of unexpected stability and reactivity

Attempts to prepare JNJ 26273364, a highly functionalized pyrazole-based CCK₁ receptor antagonist, using a carboxylation reaction led to a series of unexpected results. This work demonstrated the unique reactivity and stability of the highly functionalized Z-alkene functionality present around the pyrazole.     

New deuterated oligo(ethylene glycol) building blocks and their use in the preparation of surface active lipids possessing labeled hydrophilic tethers

For the introduction of additional analysis protocols of tethered molecules, a method is presented to prepare functionalized, deuterated oligo(ethylene glycols) from ethylene glycol-d4. Partial oligomerization of ethylene glycol-d4 and conversion to ditosylates is accompanied by coupling reactions to prepare doubly benzyl protected oligo(ethylene glycols) with two to five repeating units. The tetramer bearing 16 deuteria was elaborated at both ends to eventually prepare 2,3-di-O-phytanyl-sn-glycerol-1-tetraethylene glycol-d,l-alpha-lipoic acid ester (DPTL), which bears a fully deuterated tetra(ethylene glycol) spacer group. Through linking of functionalized components, an analogue of DPTL possessing an octa(ethylene glycol) spacer group was prepared, both in deuterated and unlabeled form.     

Octacoordinate carbons encaged inside carborane clusters: a density functional theory investigation

This work focuses on the computational design and characterization of a novel series of endohedral carborane clusters containing octacoordinate carbon centers. The structural and bonding features and the thermodynamic and kinetic stabilities are discussed extensively based on density functional theory calculations. These nonclassical carboranes are fascinating in structure not only for the octacoordinate carbon center but also for the surrounding carbon and boron ligands with inverted bonding configuration. These endohedral carboranes are higher in energy than the corresponding exohedral isomers due to the high strain in the system. A new stability rule based on the donor-acceptor model is proposed to predict the stability ordering for these carborane isomers. In addition, some of these octacoordinate carboranes might have relatively high kinetic stabilities, which is rather hopeful for the experimental syntheses.     

Visible-Light-Induced Photoreduction of Carborane Phosphonium Salts: Efficient Synthesis of Carborane-Oxindole-Pharmaceutical Hybrids

Visible-light-induced photoreaction of carboranes is an effective approach to prepare carborane-containing compounds. While several methods involving boron-centered carboranyl radicals have been established, those for carbon-centered carboranyl radicals are underdeveloped, except for the UV-light-promoted photohomolysis. Herein, we describe a simple but effective approach to access carbon-centered carboranyl radicals by photoreduction of carborane phosphonium salts under blue light irradiation without using transition metals and photocatalysts. The utility of the method was demonstrated by successfully preparing a range of carborane-oxindole-pharmaceutical hybrids by radical cascade reactions. Computational and experimental studies suggest that the carbon-centered carboranyl radicals are generated by single-electron transfer of the photoactive charge-transfer complexes between the salts and the additive potassium acetate.     

General Access to Aminobenzyl‐o‐carboranes as a New Class of Carborane Derivatives: Entry to Enantiopure Carborane–Amine Combinations

The convenient synthesis of original aminobenzyl‐o‐carboranes, which represent a new class of nitrogenated carborane derivatives, is described. These novel compounds have been efficiently prepared starting from commercially available aromatic aldehydes and monosubstituted o‐carboranes via carboranyl alcohols and chlorides as intermediates. The key step of this methodology is a selective nucleophilic amination under mild conditions that allows the formation of the expected amines while limiting the partial deboronation of the carborane cluster. This general strategy has been applied to the preparation of a wide variety of aminobenzyl‐o‐carboranes. The extension of this pathway to the synthesis of enantiopure carborane–amine combinations is also described.     

Hypercarbons in polyhedral structures

Though carbon is mostly tetravalent and tetracoordinated, there are several examples where the coordination number exceeds four. Structural varieties that exhibit hypercarbons in polyhedral structures such as polyhedral carboranes, sandwich complexes, encapsulated polyhedral structures and novel planar aromatic systems with atoms embedded in the middle are reviewed here. The structural variety anticipated with hypercoordinate carbon among carboranes is large as there are many modes of condensation that could lead to large number of new patterns. The relative stabilities of positional isomers of polyhedral carboranes, sandwich structures, and endohedral carboranes are briefly described. The mno rule accounts for the variety of structural patterns. Wheel-shaped and planar hypercoordinated molecules are recent theoretical developments in this area.     

New method to prepare peptide-oligonucleotide conjugates through glyoxylic oxime formation

A new method to prepare peptide-oligonucleotide conjugates through chemoselective glyoxylic oxime linkage is reported. A novel phosphoramidite reagent, readily accessible from serine, was prepared and used in automated DNA synthesis to prepare oligonucleotides carrying a glyoxylic aldehyde functionality at the 5' terminus. This was efficiently coupled to a peptide functionalized with an aminooxy group. The method could be of general use to prepare a broad range of oligonucleotide conjugates.     

Structures and Syntheses of Carboranes

Following a discussion of bonding, the structures of the known carboranes of the clovo type and of the incompletely condensed types are described; the recently discovered carboranes with high carbon contents, such as tetracarbahexaborane (“boracarbane”) are also discussed. The preparation of carboranes from polyboranes and the possibility of obtaining organo carboranes from organoboranes are then described. Some rearrangements which take place within the carborane skeleton are also mentioned.     

二十面体碳硼烷的亲电取代定位效应理论研究

利用Ｇａｕｓｓｉａｎ９４从头计算程序在６－３１Ｇ基组下对二十面体碳硼烷Ｃ２Ｂ１０Ｈ１２、ＣＢ１１Ｈ１２＾－及其衍生物ＣＢ１１Ｈ１１Ｂｒ＾－进行了从头计算，结果表明，在亲电取代反应中，杂原子Ｃ具有对、空间定位效应，取代基－Ｂｒ为邻，对位定位基因，与实验事实相符。