Lanthanide reagents in solid phase synthesis

From solid-supported ytterbium(III) catalysts to linkers cleaved by electron transfer from samarium(II) species, lanthanide reagents are beginning to find widespread application in solid phase organic synthesis. This tutorial review introduces the use of lanthanide(III) Lewis acids and lanthanide(IV) oxidants in solid phase chemistry before concentrating on the growing use of lanthanide(II) reagents in the area.     

Titrimetric determination of thiols: Tetrathionate, iron(III), cystine and hexacyanoferrate(III) as thiol reagents

Four analytical reagents, tetrathionate, iron(III), cystine and hexacyanoferrate(III) have been tested with respect to their specificity for oxidation of thiols to disulphides. Of a number of thiols studied, most have a strong tendency to oxidize beyond the disulphide stage with several of the commonly employed reagents. Tetrathionate, cystine and hexacyanoferrate(III) function in phosphate buffer of pH 7, but iron(III) does not require rigid control of pH, although the solution should be only feebly acidic. The reagents were used in excess and the thiosulphate or cysteine formed in the reaction of thiols with tetrathionate or cystine respectively was determined. The residual iron(III) was measured by adding ascorbic acid or mercaptoacetic acid and titrating with 2,6-dichlorophenolindophenol or iodine monochloride respectively; surplus hexacyanoferrate(III) was back-titrated with ascorbic acid. All four reagents react selectively with thiols even in the presence of several possible interfering substances and afford results that are accurate and precise.     

Remote stereocontrol using functionalized allylmetal reagents

Alk-2-enyl(trialkyl)stannanes with heteroatom substituents at the 4-, 5-, and 6-positions are transmetallated stereoselectively using tin(IV) halides to generate allyltin trihalides, which react with aldehydes to give (3Z)-homoallylic alcohols with efficient 1,5-, 1,6-, and 1,7-stereocontrol. This chemistry has been used to develop new strategies for natural product synthesis. Because of the toxicity of organotin reagents and the problems in removing organotin residues from reaction products, alternative procedures that avoid the use of organotin reagents have been investigated. To date, alk-2-enylgermanium reagents have been shown to deliver effective 1,5- and 1,6-stereocontrol, which is analogous to that observed for the organotin compounds. Organobismuth intermediates, which can be generated from allyl bromides and zinc-bismuth(III)iodide, react with aldehydes with efficient 1,5-stereocontrol which is complementary to that observed with the organo-stannanes or -germanes in that (3E)-homoallylic alcohols are obtained.     

Synthesis,characterization, and initial reaction study of two new bicyclic hypervalent iodine(III) reagents

The synthesis of two new bicyclic hypervalent iodine(III) reagents 5 and 6 is described along with their corresponding X-ray crystal structures for the first time. A detailed comparison in the bond lengths and bond angles of reported bicyclic hypervalent iodine(III) reagents is also presented. Furthermore, an initial study shows that these two hypervalent iodine(III) reagents could promote the dipeptide coupling reaction.     

Synthesis and reactivity of carbazole-containing hypervalent iodine(III) reagents

A range of bench-stable carbazole-containing hypervalent iodine(Ⅲ) reagents were synthesized by I-N bond formation in good yields.This kind of benziodoxolone reagents was used for a C-N coupling reaction to introduce a carbazole group to aromatic heterocycle compounds.     

Selective detection of bismuth(III) and iron(II) ions with certain new reagents

Isoperthiocyanic acid (3-amino-5-thione-1,2,4-dithiazole) (I), tetraethylthiuram monosulphide ("Tetmosol") (II), eosin (III), and mercurochrome (IV) are used as new qualitative reagents for bismuth, III and IV are also used for detection of iron(II). A conc. sulphuric acid solution of I, or an acctone solution of II, when treated with bismuth in presence of potassium iodide, gives a deep red or reddish-orange precipitate, characteristic of bismuth. Bismuth in presence of III or IV gives a heavy and characteristically bright deeppink precipitate on addition of ammonia. With I, 1 mug of bismuth may be detected with a dilution limit of 1:50,000. Sb(III) and As(III) do not interfere in any of these tests. Iodides interfere only when I and II are used as reagents. Pb, Cu(II). and Fe(III) interfere with III and IV. I and II are also proposed as reagents for iodide; nitrites would interfere. III and IV, with iron(II) on addition of ammonia, produce a precipitate with highly intense green fluorescence. No other common cation [including Fe(III)] or anion interferes. The limit of detection is 3 mug ml .     

Unstable reagents in flow analysis

Investigations on the analytical applications of unstable oxidizing and reducing agents in aqueous solutions in flow analysis are reviewed. The generation of these unstable reagents in flow eliminates the disadvantages of their application in batch, i.e., frequent standardization, difficulties with storage and time consumption. The advantages of flow analysis (speed, ease of operation and good precision) remain. Limits of determination of 10^?5?10^?6 mol l^?1 can be achieved in several cases with spectrophotometric or amperometric detection. Uranium(III) and silver(II) are especially promising reagents. Possibilities for future work are discussed.     

Organocerium reagents. Nucleophilic addition to easily enolizable ketones

Organocerium reagents, prepared from organolithiums and anhydrous cerium (III) chloride, react cleanly with easily enolizable ketones to afford the addition products in good to excellent yields.     

A general method for one-step synthesis of monofluoroiodane(III) reagents using silver difluoride

Herein we report a new general method for one-step synthesis of four kinds of fluoroiodane(III) reagents by treating the corresponding aryl iodides with silver difluoride (AgF₂). This is the first method applicable for the synthesis of all four fluoroiodane(III) reagents including p-iodotoluene difluoride (1), fluoro-benziodoxole (2), fluoro-benziodoxolone (3), and fluoro-N-acetylbenziodazole (4). AgF₂ was firstly employed in the direct oxidative fluorination of iodobenzene and thus has shown its outstanding oxidation and fluorine-transfer ability. The use of AgF₂ has improved the synthesis of fluoroiodane(III) reagents by shortening the reaction steps, avoiding the use of hazardous reagents, and simplifying the experimental operations. It was worth noting that we have developed the first one-step direct synthetic method for 3, while 3 can only be synthesized through Cl→F ligand exchange reaction previously.     

New phosphorylating reagents for deoxyribonucleosides and oligonucleotides

New phosphorylating reagents 1 and 2 were prepared in three steps from 4-hydroxybenzaldehyde. They showed good efficiency in the solid phase synthesis of 5′-phosphate monoester nucleosides. End-phosphate DNA sequence synthesis demonstrated the efficiency of the new reagents (1 and 2) according to the general procedure of automated DNA synthesis. The oxidation of P(III) to P(V) and the removal of benzyl protecting groups were achieved in a single step by treatment with a 0.02 M I₂/pyridine/H₂O solution. Due to this one-pot treatment, it is possible to use the phosphorylating reagents (1 and 2) for the synthesis of base-sensitive ODNs. The reagents 1 and 2 are unique among phosphorylating reagents.     

The applications of hypervalent iodine(III) reagents in the constructions of heterocyclic compounds through oxidative coupling reactions

Hypervalent iodine(Ⅲ)reagents have been vastly used in many useful organic transformations.In this review article,we highlight the strategies that used the common hypervalent iodine(Ⅲ)reagents as oxidants to synthesize the heterocyclic compounds,based on the patterns of bond formation during the construction of the heterocyclic backbones.     

Cerium chloride-promoted nucleophilic addition of grignard reagents to ketones an efficient method for the synthesis of tertiary alcohols

In the presence of anhydrous cerium(III) chloride, Grignard reagents react with Ketones to afford addition products in high yields, even though the substrates are susceptible to abnormal reactions with Grignard reagents alone.     

Modification of the alumina surface with polyfunctional organic reagents

The sorption of polyfunctional organic reagents on the surface of alumina was studied. The optimum conditions of modification were found. A sorption mechanism was suggested. Sorption was found to depend on the structure of the modifier reagent. The sorption of iron(III) and cobalt(II) on alumina modified with nitroso-R-salt was studied.     

Addition of organocerium reagents to morpholine amides: synthesis of important pheromone components of Achaea janata

Readily preparable morpholine amides hitch in good yields with organocerium reagents to produce ketones. Even in the presence of substrates and reagents with high steric hindrance, the organometallic compounds prepared from dry cerium(III) chloride and organomagnesium or organolithium compounds at -78 degrees C add cleanly to morpholine amides. The low cost of starting materials makes this new scheme of synthesis very interesting for the preparation of biologically important pheromones.     

Test films for test-determinations on the base of reagents, immobilized in gelatinous gel

Gelatinous solidified layers of the photographic film were used for the immobilization of analytical reagents for detection and determination of reductants and primary aromatic amines. It was shown, that the films with immobilized iron(III)-Dipy or iron(III)-Phen complexes as test films for reductants and films with immobilized aldehydes (vanillin, p-dimethylaminobenzaldehyde) as the test films for primary aromatic amines can be used. The improving of reagents immobilization in the presence of sodium dodecylsulfate micelles was obtained. Metrological characteristics of visual detection and photometric determination using test films were evaluated on the basis of statistical approach and investigation of detection probability distribution in the concentration range of unreliable reaction. The suggested test films for the determination of ascorbic acid, analgin (dipyrone), novocaine and streptocide in drugs were examined successfully.     

Cyclopentadienyl benzamidinato chromium complexes as models for alkyl halide activation by chromium reagents

Cyclopentadienyl complexes of Cr(II) and Cr(III) are stabilized by bis(trimethylsilyl)benzamidinato ligands, allowing the resulting well-defined compounds to serve as models for alkyl halide activation by mid-valent Cr-based reagents.     

Oxidative-substitution reactions of polycyclic aromatic hydrocarbons with iodine(III) sulfonate reagents

Polycyclic aromatic hydrocarbons (PAH) undergo regioselective oxidative-substitution reactions with iodine(III) sulfonate reagents in dichloromethane to give the corresponding aryl sulfonate esters. The use of [hydroxy(tosyloxy)iodo]benzene in conjunction with trimethylsilyl isothiocyanate leads to thiocyanation of the PAH nucleus.     

Highly shifted LIPOCEST agents based on the encapsulation of neutral polynuclear paramagnetic shift reagents

Improved LIPOCEST MRI contrast agents with highly shifted intraliposomal water protons were prepared by entrapping neutral polynuclear Tm(III)-based paramagnetic shift reagents in phospholipidic vesicles.     

Analytical complexation reactions of organic reagents with metal ions in a solidified gelatin gel

Solidified gelatin gel is an original medium for analytical complexation reactions between organic reagents and element ions. The chemical nature of this biopolymer enables the electrostatic immobilization of organic reagents bearing anionic groups, like Arsenazo III, by protonated amino groups of the macromolecule. It was shown that the exhaustive capacity of the matrix towards organic sulfonate reagents differing in the number of sulfonic groups and the geometrical size of molecules was related to the specific properties of matrices and the fractal properties of the gel surface. It was found that the conditions for the reactions of complex formation and decomposition of the reagents immobilized in the gel were identical to those for reactions in aqueous solutions. It was proved that the gel fixed on a transparent triacetylcellulose support could be used as a component of sensing elements of optical sensors and/or test systems. This was demonstrated by the examples of the determination of La(III), Th(IV), U(VI), Ca(II), and SO₄²⁻.     

1,2-Diarylethylenediamines as fluorogenic reagents for catecholamines

Twenty-eight 1,2-diarylethylenediamines were investigated in a search for highly sensitive fluorogenic reagents for catecholamines (norepinephrine, epinephrine and dopamine). They all react with epinephrine used as a model catecholamine under mild conditions (pH 6.5–6.8, 37–50°C) in the presence of potassium hexacyanoferrate (III) to produce fluorescence. Of the compounds tested, 1,2-bis(3,4-dimethoxyphenyl)ethylenediamine, 1,2-bis(4-methoxyphenyl)ethylenediamine and 1,2-bis (4-ethoxyphenyl)ethylenediamine, all in the meso-form, are the most sensitive for all the catecholamines. 1,2-Diphenylethylenediamine, 1,2-bis(4-methoxyphenyl)ethylenediamine and 1,2-bis (4-methylphenyl) ethylenediamine in the dl-form are more sensitive to dopamine than the corresponding compounds in the meso-form. Catecholamines can be determined at concentrations as low as 10–15 pmol ml^?1 by using those compounds as reagents. The reactions of other catechol compounds are reported. Other types of biologically important compounds do not interfere.