Modified aryldifluorophenylsilicates with improved activity and selectivity in nucleophilic fluorination of secondary substrates.

Nucleophilic fluorination of secondary aliphatic substrates, especially of halides, still remains a challenge. Among the available reagents, TBAT belongs to one of the best choices due to its stability, affordable price and low toxicity. With the aim to improve its selectivity, we synthesized three analogues modified in the aryl part of the TBAT reagent with one or two electron donating methoxy groups or with one electron withdrawing trifluoromethyl group.

Quaternary ammonium fluorides and difluorosilicates as nucleophilic fluorination reagents.

TBAT (tetrabutylammonium difluorotriphenylsilicate) is an excellent homogeneous nucleophilic fluorination reagent, but a high excess of the reagent was reported to be essential. We hence optimized the reaction conditions and compared its nucleophilic fluorination reactivity with that of other common commercial nucleophilic fluorination reagents, such as anhydrous TBAF and TASF (tris(dimethylamino)sulfonium difluorotrimethylsilicate). As the substrates, we employed a standard set of primary and secondary octyl substrates under identical conditions.

From cyclic (alkyl)(amino)carbene (CAAC) precursors to fluorinating reagents. Experimental and theoretical study.

Addition of anhydrous HF to the hydrochloride [CAACH][Cl(HCl)] resulted in the formation of salts with high HF content. By stepwise removal of HF , we selectively prepared [CAACH][F(HF)] (3) and [CAACH][F(HF)] (4). We also characterised a salt with [F(HF)] anions within the structure of [CAACH][F(HF)] (5).

Non-Symmetrical Tetrafluoroalkadienes Synthesized by ROCM of 3,3,4,4-Tetrafluorocyclobutene.

As the first known example of ring-opening cross metathesis (ROCM) of polyfluorinated strained cyclobutenes, ROCM of 3,3,4,4-tetrafluorocyclobutene with electronically rich alkenes, catalyzed by Grubbs or Hoveyda-Grubbs 2 generation precatalysts, gave a small library of non-symmetrical isolated dienes bearing a tetrafluoroethylene spacer between the double bonds. 1-Butoxy-3,3,4,4-tetrafluorohexa-1,5-diene thus formed underwent subsequent regioselective cross metathesis (CM) with a series of styrenes, catalyzed by Hoveyda-Grubbs 2 generation precatalyst, leading to non-symmetrically substituted dienes. 6,6-Dibutoxy-3,3,4,4-tetrafluorohex-1-ene, formed by regioselective butoxylation of 1-butoxy-3,3,4,4-tetrafluorohexa-1,5-diene, was dihydroxylated and cyclized to the corresponding 3,3,4,4-tetrafluorohexopyranose.

Synthesis of imidazolium-based pentacoordinated organofluorosilicate and germanate salts.

The syntheses of a new triphenyldifluorogermanate and various pentacoordinated organofluorosilicates are presented. The fluorogermane and fluorosilane compounds were obtained from the corresponding chlorosilanes and chlorogermane by halogen substitution with KF. Subsequent reaction with the imidazolium-based fluoride reagent [IPrH][F] (1,3-bis(2,6-diisopropylphenyl)imidazolium fluoride) led to the formation of [IPrH][PhSiF] (1), [IPrH][PhSiF] (3), [IPrH][EtSiF] (4), [IPrH][PhSiF] (5), [IPrH][EtSiF] (6) and [IPrH][PhGeF] (7).

Electrochemical investigation of structurally varied azinium scaffolds.

Inspired by the successful utilization of aziniums as anolytes in redox-flow batteries, we have designed and prepared a systematically extended series of (di)azinium compounds based on pyrazine, bipyridine, 1,5-naphthyridine, 3,8-phenanthroline, ()-4,4'-diazastilbene and 1,2-bis(pyridin-4-yl)acetylene. It has been revealed that the fundamental electrochemical properties are affected mostly by the water-solubility and chemical stability of the particular redox forms. Based on the systematically evolved azinium structure and gathered electrochemical data, structure-property relationships were thoroughly elucidated.

Mechanism of Alkyl Chloroformate-Mediated Esterification of Carboxylic Acids in Aqueous Media.

The protection of carboxyl groups by esterification has been the most common method in macroscale and microscale chemistries. The esterification is usually conducted under anhydrous conditions; however, in biological chemistry and related fields, the reaction is of major concern in aqueous environments. Immediate esterification of the carboxyl in aqueous alcoholic media driven by an alkyl chloroformate and pyridine has been such a method which has found widespread use in many research and industrial laboratories.

Redox Property Tuning in Bipyridinium Salts.

Bipyridinium salts are currently very popular due to their perspective applications in redox flow batteries. Hence, we designed and prepared a series of bipyridiniums based on 2,2'-, 3,3'-, and 4,4'-bipyridine and 2,2'-bipyrimidine. The straightforward synthesis utilizes commercially or readily available starting compounds and their direct -alkylation, mostly using 1,3-propanesultone.

Ring-closing metathesis of prochiral oxaenediynes to racemic 4-alkenyl-2-alkynyl-3,6-dihydro-2-pyrans.

The prochiral 4-(allyloxy)hepta-1,6-diynes, optionally modified in the positions 1 and 7 with an alkyl or ester group, undergo a chemoselective ring-closing enyne metathesis yielding racemic 4-alkenyl-2-alkynyl-3,6-dihydro-2-pyrans. Among the catalysts tested, Grubbs 1st generation precatalyst in the presence of ethene (Mori conditions) gave superior results compared to the more stable Grubbs or Hoveyda-Grubbs 2nd generation precatalysts. This is probably caused by a suppression of the subsequent side-reactions of the enyne metathesis product with ethene.

Computational study of productive and non-productive cycles in fluoroalkene metathesis.

A detailed DFT study of the mechanism of metathesis of fluoroethene, 1-fluoroethene, 1,1-difluoroethene, cis- and trans-1,2-difluoroethene, tetrafluoroethene and chlorotrifluoroethene catalysed with the Hoveyda-Grubbs 2(nd) generation catalyst was performed. It revealed that a successful metathesis of hydrofluoroethenes is hampered by a high preference for a non-productive catalytic cycle proceeding through a ruthenacyclobutane intermediate bearing fluorines in positions 2 and 4. Moreover, the calculations showed that the cross-metathesis of perfluoro- or perhaloalkenes should be a feasible process and that the metathesis is not very sensitive to stereochemical issues.

Transition metal complexes bearing NHC ligands substituted with secondary polyfluoroalkyl groups.

Using three different approaches, racemic 1-(perfluoroalkyl)ethylamines were synthesized from perfluoroalkyl iodides or perfluoroalkanoic acids, and further transformed to the corresponding N,N'-disubstituted ethane-1,2-diimines and ethane-1,2-diamines as mixtures of diastereoisomers. Their cyclization afforded imidazolium or dihydroimidazolium salts, which led to silver or palladium complexes bearing NHC ligands substituted with secondary polyfluoroalkyl groups. The palladium complexes bearing a throwaway 3-chloropyridine ligand proved to be moderately active in the model Suzuki-Miyaura coupling.

Interaction of ionic liquids ions with natural cyclodextrins.

The interaction of natural α-, β-, and γ-cyclodextrins (CDs) with 14 hydrophobic ionic moieties of ionic liquids (ILs) was systematically examined in dilute aqueous solutions using isothermal titration microcalorimetry (ITC) and NMR spectroscopy. The studied cationic and anionic moieties involved some recently developed heavily fluorinated structures, as well as some others of common use. To isolate the effect of a given ion, the measurements were performed on salts containing the hydrophobic IL ion in question and a complexation-inactive counterion.

Trifluoromethylated (tetrahydropyrrolo) quinazolinones by a new three-component reaction and facile assignment of the regio- and stereoisomers formed by NMR spectroscopy.

A new three-component cyclisation reactions of methyl 3,3,3-trifluoropyruvate, 2-aminobenzylamine and oxo compounds afforded tetrahydropyrroloquinazolinones of the types 4 and 5 as mixtures of regio- and stereoisomers. Whereas standard 1D NMR spectroscopy was used for a facile assignment of the cyclization regioisomers, a combination of homo (proton-proton) and heteronuclear (proton-fluorine) NOE experiments allowed the determination of the relative configuration on stereogenic centres. The structure of some compounds was also confirmed by the X-ray diffraction.

[Selenium deficiency of west Bohemia population].

To estimate status and intake of selenium in inhabitants of the most Western region of the Czech Republic (Cheb region) 241 serum, 404 urine and 30 hair samples from randomly selected persons in the age between 6 and 65 years is performed. Serum and hair samples were analysed by means of instrumental neutron activation analysis (INAA), while Se in urines was detected by means of fluorimetry. Urine iodine was determined in the same group by Sandell-Kolthoff method for the possibility to detect concomitant Se and I deficiency and/or correlations between these two essential trace elements necessary for metabolism of thyroid hormones.

Effect of iodine and selenium upon thyroid function.

Iodine is an essential element with unique role in organism: it is indispensable component of thyroid hormones. After binding with specific nuclear receptor, T3/T4 induce transcription of genetic code via mRNA and regulate proteosynthesis in most tissues. Thyroid hormones regulate rate of metabolic processes and consequently development of organism.

Characterization of selenium status of inhabitants in the region Usti nad Orlici, Czech Republic by INAA of blood serum and hair and fluorimetric analysis of urine.

Selenium is an essential trace element and its insufficient status may cause serious health complications for both individuals and the whole populations. To investigate the selenium status of the subpopulation in northeastern Bohemia represented by the region Ustí nad Orlicí, 253 serum, 469 urine, and 31 hair samples from 470 randomly selected volunteers between 6 and 65 yr of age have been analyzed for selenium concentration. Serum and hair Se were detected by instrumental neutron activation analysis (means: 55 +/- 11 micrograms Se/L sera, 0.

INAA of serum zinc of inhabitants in five regions of the Czech Republic.

To investigate the Zn status of inhabitants of the Czech Republic, 1155 serum and 132 hair samples were analyzed for zinc content. Analyzed material was obtained from randomly selected volunteers of both sexes in the age range 6-65 yr. Subpopulations from five regions were included in the study.

Status of magnesium, selenium and iodine saturation in the population of seven regions in the Czech Republic.

In seven regions of the Czech Republic the magnesiuria and calciuria were determined photometrically using the apparatus Merck Vitalab Eclipse, the selenuria fluorimetrically and the ioduria photometrically after alkaline mineralization in the morning sample of urine (after night fasting) in subjects aged 6-65 years (3,587 probands) selected at random. The lowest magnesiuria was found in children in Klatovy district (5.36 nmol/l +/- 0.

[Selenium and the organism].

Selenium is an essential trace element for animals. It is biologically active as selenocysteine in the active centre of selenoproteins with enzymatic functions. Incorporation of selenocysteine occurs on the basis of genetic expression and selenium is the only trace element under direct genetic control.

[Changes in urinary calcium and magnesium levels during supplementation with iodine and selenium].

The authors examined 31 children aged 10-13 years before and after 5-month administration of 100 micrograms iodine (as iodide 100 Merck) and 57 university students (age 18-23 years) divided into four groups. The control group of 15 students received placebo daily, 20 students took selenium (50 micrograms selenium Merck), 8 students iodine (100 micrograms iodide) and 14 students a combination of equal amounts of both elements. The authors investigated the calciuria, mangesiuria and calcium/creatinine ratio and magnesium/creatinine ratio.

[Status and selenium intake as related to the thyroid gland in the population of Znojmo].

In a group of 360 people aged 6-65 years of both sexes from the Znojmo area the author investigated the selenium status and intake by serum analyses (246 cases), urine analyses (356 cases) and hair analyses (28 analyses in middle-aged men). By correlation analysis the author investigated the relationship of selenium and metabolic and peripheral thyroid parameters. From the low selenium concentration in all investigated materials (42 micrograms Se/l serum, 8.

Correlations between parameters of body selenium status and peripheral thyroid parameters in the low selenium region.

The following were measured in 380 male and female inhabitants of Prague (n the age range 6-65 years):selenium in serum and urine, iodine in urine, thyroid-stimulating hormone, thyroid volume, thyroxine (T4), triiodothyronine (T3), ankle jerk time, pulse rate and body fat. Correlations were calculated to assess the influence of Se upon the thyroid hormone parameters and their peripheral effects in Se-deficient regions both by using the linear correlation analysis and by using the multiple linear correlation analysis and the analysis of variance. Many significant linear correlations were found for whole groups of examined persons, for the individual groups (boys, men, girls and women) as well as for subgroups, according to the age and sex.

Evaluation of selenium supply and status of inhabitants in three selected rural and urban regions of the Czech Republic.

Blood serum selenium of 65 men and hair selenium of 77 men from three regions of the Czech Republic (CR) were analyzed by neutron activation analysis, and 202 samples of urine from the same populations were analyzed for Se by the fluorimetric method to assess selenium status of these regions. Low status (53 micrograms Se/L of serum and 0.29 micrograms Se/g lyophilized hair as means) and very low urine selenium (8.

Levels of some trace elements in serum of Prague inhabitants measured by INAA.

Sera of 240 randomly selected Prague inhabitants of both sexes from ages 6 to 65 yr were analyzed by instrumental neutron activation analysis (INAA) for Fe, Zn, Se, Rb, Cs, and Sc. Significant differences were found between serum Fe and Zn levels of men from Prague and from rural regions of Central Bohemia. Concentration of Se was one of the lowest in Europe and exhibited age-dependent, but not sex-dependent changes.

Selenium and rubidium changes in subjects with pathologically altered thyroid.

Concentrations of selenium and rubidium in groups of subjects with hyperthyroidism, carcinomas, or adenomas and in controls were determined by neutron activation analysis with coirradiated inorganic standards and IAEA reference material. Se was decreased in all pathological groups with the greatest modification in thyroids with carcinomas. Rb was elevated in all pathological groups with the greatest increase in carcinomas as well.