Potent estrogen agonists based on carborane as a hydrophobic skeletal structure. A new medicinal application of boron clusters.

Metallacarboranes in the new millennium

The discovery of important roles of C-nitroso compounds in various biological metabolic processes has generated a renewed interest in the general chemical properties of nitrosoalkanes (R–N=O; R =alkyl) and nitrosoarenes (ArNO; Ar =aryl), two important subsets of this general class of compounds. For example, the identification of the nitrosobenzene adduct of hemoglobin as a product of nitrobenzene poisoning1,2 and the realization that some amine-containing drugs may be metabolized to nitroso derivatives3–6 led to an increased desire to study the fundamental biochemical properties of this fascinating class of C-nitroso compounds. To this end, many studies have been reported on the fundamental chemistry of C-nitroso compounds under conditions that either stabilize the C-nitroso functionality or enhance their reactivity toward isomerization or reactivity with substrates.

A major difficulty in C-nitroso chemistry, however, is that the high reactivity of these compounds necessarily imposes constraints upon the methods employed for their preparation, particularly with regard to the yield of the desired product. For example, the ease of oxidation of the desired nitroso compound (if oxidation of a suitable precursor is the chosen synthetic route) to its nitro derivative can significantly reduce the yield of the nitroso product. Similarly, the ease of isomerization of R2C(H)NO compounds to the corresponding oximes R2C=NOH can restrict the choice of solvent for the preparation of primary and secondary nitrosoalkanes. A further consideration to be borne in mind is the possibility of reaction of the C-nitroso compound with the starting material and/or preparative reagents. There is, however, a considerable variety of synthetic routes available for the high-yield preparations of C-nitroso compounds (monomers or dimers; Figure 1), some of which have been in regular use for well over 100 years.




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Figure 1



Some earlier reviews of this area have been published. Book chapters by Sandler and Karo (in 1986)7 and by Williams (in 1988)8 present the most detail to date on the experimental techniques for preparations of C-nitroso compounds. Other useful earlier reviews are those by Touster,9 Boyer,10 Metzger and Meier,11 Seidenfaden,12 and Katritzky et al.13

Given the renewed interest in the study of the biological and environmental consequences of C-nitroso compound formation, it is not surprising that many new and/or improved procedures for the preparations of these compounds have been developed over the last two decades. In this review, we present a comprehensive review of the synthetic procedures for the preparation of C-nitroso compounds and place these procedures in proper historical context. We also include a small number of routes to the production of C-nitroso compounds that may have preparative possibilities or which require improved workup methods. We indicate, when known, whether the method of preparation is applicable to all types of C-nitroso compounds or only to separate classes such as nitrosoarenes, nitrosoalkanes, nitrosohomocycles, or nitrosoheterocycles. Nitrosoalkenes are considered in a separate section. The coordination chemistry of C-nitroso compounds with metals has been reviewed recently.6,14

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Preparations of C-Nitroso Compounds

Cyclic oxonium derivatives of polyhedral boron hydrides are a relatively new class of boron compounds. They have great potential for the modification of various types of organic and bioorganic molecules and the synthesis of compounds that could be used in different fields from the treatment of nuclear wastes to the treatment of cancer. In the present Perspective we would like to present an overview of the results of the preparation and synthetic application of these compounds.

Cyclic oxonium derivatives of polyhedral boron hydrides and their synthetic applications

Hydroboration of olefins. A remakably fast room-temperature addition of diborane to olefins

It was found that mercuric chloride has a specific oxidative effect on the anions of dicarbadodecahydronidoundecaborates in THF or pyridine, which consists in the preferential replacement of hydride hydrogen by the ligand in the 8 position of the anion.

Oxidation of dicarbadodecahydronidoundecaborate anions by mercuric chloride in tetrahydrofuran and pyridine

The molecular structure of p-phospha- and p-arsacarboranes 1,12-XCHB10H10 (X = P, As) by gas phase electron diffraction

The reaction of DMFA or DMSO with 1-phenyl-2-lithia-1,2-dicarba-closo-dodecaborane results in unusual opening of the closo structure, which leads to the formation of the tetramethylammonium and methylpyridinium salts of the 7-phenyl-12-(1′-phenyl-1′,2′-dicarba-closo-dodecaboran-2′-yl)-7, 8-dicarba-nido-dodecaborate anion, whose structure was established by x-ray diffraction analysis.

Molecular structure of the 7-phenyl-12-(1′-phenyl-1′,2′-dicarba-closo-dodecaboran-2′-yl)-7, 8-dicarba-nido-dodecaborate anion-a representative of a new type of dicarba-nido-dodecaborate anion formed as a result of the opening of the closo structure of 1-phenyl-2-lithia-1,2-dicarba-closo-dodecaborane in the presence of HCONMe2 or Me2SO

1.

1-Hydroxy-o-earboranes and 1-hydroxy-m-carboranes were synthesized by the reaction of carboranyllithiums with benzoyl peroxide.




2.

The 1-hydroxycarboranes have considerable acidity. The apparent dissociation constants of the 1-hydroxy-o-carboranes and the 1-hydroxy-m-carboranes were measured in 50% alcohol.




3.

The 1-hydroxy-o-carboranes react with diazomethane to form 1-methoxy-o-carboranes.




4.

1-Acetoxy- and 1-benzoxycarboranes were obtained from the 1-hydroxycarboranes.

Preparation and properties of 1-hydroxycarboranes

1.

A method for obtaining mercapto derivatives of the barenes by the action of sulfur on metal (Li, Na, K) derivatives of the barenes in liquid ammonia has been proposed.




2.

Barene disulfides have been obtained from barene mercapto derivatives.




3.

Hydrogen peroxide in acetic acid readily oxidizes the boron skeleton of B9H11C2RR′ to boric acid.

G. G. Zhigareva

Papers

Oxidation of dicarbadodecahydronidoundecaborate anions by mercuric chloride in tetrahydrofuran and pyridine

The molecular structure of p-phospha- and p-arsacarboranes 1,12-XCHB10H10 (X = P, As) by gas phase electron diffraction

Preparation and properties of 1-hydroxycarboranes

Synthesis and some reactions of mercapto derivatives of barenes