The unique role of fluorine in the design of active ingredients for modern crop protection

Intermolecular aminotrifluoromethylation of alkenes by visible-light-driven photoredox catalysis

Intermolecular aminotrifluoromethylation of alkenes catalyzed by [Ru(bpy)3](2+) under visible light irradiation has been explored. The present photocatalytic protocol achieves highly efficient and regioselective difunctionalization of C═C bonds, leading to a variety of β-trifluoromethylamines. The reaction is applied to "late-stage aminotrifluoromethylation" of steroid and amino acid scaffolds.

Mild copper-mediated fluorination of aryl stannanes and aryl trifluoroborates

This communication describes a mild copper-mediated fluorination of aryl stannanes and aryl trifluoroborates with N-fluoro-2,4,6-trimethylpyridinium triflate. This protocol demonstrates broad substrate scope and functional group tolerance, and does not require the use of any noble metal additives. The reaction is proposed to proceed via an arylcopper(III) fluoride intermediate.

Catalytic hydrotrifluoromethylation of unactivated alkenes

A visible-light-mediated hydrotrifluoromethylation of unactivated alkenes that uses the Umemoto reagent as the CF(3) source and MeOH as the reductant is disclosed. This effective transformation operates at room temperature in the presence of 5 mol % Ru(bpy)(3)Cl(2); the process is characterized by its operational simplicity and functional group tolerance.

An easy access to fluoroalkanes by deoxygenative hydrofluorination of carbonyl compounds via their tosylhydrazones

An efficient and operationally simple synthesis of fluoroalkanes by deoxygenative hydrofluorination of carbonyl compounds via their tosylhydrazone surrogates is reported. The reaction can be carried out in a one-pot procedure directly from carbonyl compounds.

The toxicity of the N-hydroxy and 6-hydroxy metabolites of 3,4-dichloropropionanilide does not depend on calcium release-activated calcium channel inhibition

Each year ~1 billion kg of herbicides are used worldwide to control the unwanted growth of plants. In the United States, over a quarter of a billion kg of herbicides are used, representing 28% of worldwide use. (Kiely, T., Donaldson, D., and Grube, A. [2004]. Pesticide Industry Sales and Usage. 2000 and 2001 Market Estimates. Available at: http://www.epa.gov/pesticides/pestsales/01pestsales/market_estimates2001.pdf. Accessed October 25, 2012.) Propanil (3,4-dichloropropionanilide [DCPA]) is a commonly used herbicide in the United States, with 2-4 million kg applied annually to 2 million acres of crop land. The immunomodulatory effects of DCPA have been well documented, but limited data are available on the effects of its metabolites. (Salazar, K. D., Ustyugova, I. V., Brundage, K. M., Barnett, J. B., and Schafer, R. [2008]. A review of the immunotoxicity of the pesticide 3,4-dichloropropionanalide. J. Toxicol. Environ. Health B Crit. Rev. 11, 630-645.) In mammals, hepatic enzymes metabolize DCPA, resulting in the production of 3,4-dichloroaniline (DCA). Further biotransformation of DCA leads to the production of 6-hydroxy-3,4-dichloroaniline (6OH-DCA) and N-hydroxy-3,4-dichloroaniline (NOH-DCA). We report, for the first time, the immunotoxic effects of DCPA metabolites on T-cell function. Human Jurkat T cells were exposed to varying concentrations of DCPA or its metabolites and assayed for effects on T-cell function. In addition, fluorine analogs of DCPA and DCA were investigated to determine the relative role of chlorine substituents on T-cell immunotoxicity. Here we report that exposure of Jurkat T cells to DCPA and DCA alters IL-2 secretion, nuclear factor of activated T cells (NFAT) activity, and calcium influx. However, exposure to 6OH-DCA and NOH-DCA reduces IL-2 secretion and NFAT activity but has no effect on calcium flux. When both chlorines in DCPA and DCA were substituted with fluorines all effects were abrogated. Our data indicate that metabolites of DCPA have differential effects on T-cell function and the presence of chlorines plays an important role in eliciting these effects.

Gold(I)-catalyzed aminohalogenation of fluorinated N'-aryl-N-propargyl amidines for the synthesis of imidazole derivatives under mild conditions

A procedure for the synthesis of fluorinated imidazole derivatives from propargyl amidines has been developed. Under gold(I) catalysis, propargyl amidines were converted into 5-fluoromethyl imidazoles in the presence of Selectfluor through a cascade cyclization/fluorination process. In contrast, imidazole-5-carbaldehydes were obtained in high yields when N-iodosuccinimide (NIS) was used as the halogenating reagent. The polarity of the solvent and light had significant impact on the formation of the carbaldehydes. These transformations showed excellent functional-group tolerance. An unfluorinated substrate with an electron-withdrawing group also underwent aminohalogenation to give the corresponding product in good yield. Mechanistic investigation revealed the general pathways of these transformations.

Direct conversion of indoles to 3,3-difluoro-2-oxindoles via electrophilic fluorination

3,3-Difluoro-2-oxindoles can be obtained directly from indoles in moderate yields via electrophilic fluorination using N-fluorobenzenesulfonimide as a mild fluorinating reagent. The presence of tert-butyl hydroperoxide during the reaction, together with additional heating after quenching the reaction with triethylamine, is beneficial to the formation of the desired product.

Stereoselective synthesis of conjugated fluoro enynes

Metalation-electrophilic fluorination of TMS- and TIPS-protected 1,3-benzothiazol-2-yl (BT) propargyl sulfones gave corresponding BT fluoropropargyl sulfones, Julia-Kocienski reagents for the synthesis of fluoro enynes. Both reagents reacted with aldehydes under mild DBU- or LHMDS-mediated conditions, giving high yields of conjugated fluoro enynes with E-stereoselectivity. In comparison to DBU-mediated reactions, stereoselectivity was higher in low-temperature LHMDS-mediated reactions. Two ketones were shown to react as well, using LHMDS as base. In situ removal of the TMS group gave terminal conjugated 2-fluoro 1,3-enynes. Synthetic utility of the fluoro enynes was demonstrated by conversion to internal alkynes and to stereoisomeric fluoro dienes via Sonogashira and Heck couplings.

Ready biodegradability of trifluoromethylated phenothiazine drugs, structural elucidation of their aquatic transformation products, and identification of environmental risks studied by LC-MS( n ) and QSAR

The environmental fate of transformation products from organic pollutants such as drugs has become a new research area of increasing interest over the last few years. Whereas in the past mainly parent compounds or their major human metabolites were studied, new questions have arisen what compounds could be formed during incomplete degradation in the aquatic environment and what effects the resulting transformation products might have on nature and mankind. Psychiatric drugs are among the most important prescription drugs worldwide, but so far only little data is provided upon their degradation behavior. This especially accounts for tricyclic antipsychotic drugs of the phenothiazine class. Therefore, the degradation of such drugs was investigated in this study. In this study the aerobic Closed Bottle test (The Organisation for Economic Co-operation and Development (OECD) 301D) was used to assess the ready biodegradability of three trifluoromethylated phenothiazine drugs: fluphenazine, triflupromazine, and trifluoperazine. As it is known from literature that phenothiazine drugs can easily form various photolytic transformation products under light exposure, photochemical transformation was also investigated. Since transformation products are usually not available commercially, the calculation of environmental parameters with the aid of quantitative structure activity relationship (QSAR) software was used for first evaluation of these compounds. According to the OECD test guideline, all trifluoromethylated phenothiazines had to be classified as not readily biodegradable. Chromatographic data revealed the formation of some transformation products. Comparing retention time and mass spectrometric data with the analytical results of the light exposure experiments, we found peaks with the same retention time and mass spectra. So these transformation products were not of bacterial, but photolytic, origin and are formed very quickly even under low light doses. A special chromatographic column and solvent gradient along with multiple stage mass spectrometric fragmentation experiments uncovered the presence of, in total, nine photolytic transformation products and allowed for their structural elucidation. Typical modifications of the molecules were sulfoxidation, exocyclic N-oxidation, and transformation of the trifluoromethyl to a carboxylic moiety. The obtained results of the QSAR calculations show that all transformation products are highly mobile in the aquatic environment and elimination through biotic or abiotic pathways cannot be expected. Transformation products of trifluoromethylated phenothiazine drugs have to be expected in the aquatic environment, yet nothing is known about their toxicological properties. Therefore, further risk assessment upon these drugs and their fate is strongly recommended.

Ring expansion of cyclic β-amino alcohols induced by diethylaminosulfur trifluoride: synthesis of cyclic amines with a tertiary fluorine at C3

As the replacement of a hydrogen atom by a fluorine atom in a compound can have an important impact on its biological properties, the development of methods allowing the introduction of a fluorine atom is of great importance. The scope and limitations of the ring expansion of cyclic 2-hydroxymethyl amines induced by diethylaminosulfur trifluoride (DAST) to produce cyclic β-fluoro amines was studied as well as the enantioselectivity of the process.

Palladium-catalyzed substitution and cross-coupling of benzylic fluorides

Benzylic fluorides are suitable substrates for Pd(0)-catalyzed Tsuji-Trost substitution using carbon, nitrogen, oxygen, and sulfur nucleophiles and for cross-coupling with phenylboronic acid. For the bifunctional substrate 4-chlorobenzyl fluoride, fine-tuning of the reaction conditions allows for the regioselective displacement of either the chlorine or fluorine substituent. The leaving group ability of fluoride vs other groups displaced in substitution is CF(3)CO(2) ≈ p-NO(2)C(6)H(4)CO(2) ≈ OCO(2)CH(3) > F > CH(3)CO(2), a ranking similar to allylic fluorides under Pd catalysis.

Expedient synthesis of α-substituted fluoroethenes

A mild and efficient synthesis of 1-aryl-1-fluoroethenes from benzothiazolyl (aryl)fluoromethyl sulfones and paraformaldehyde, under DBU- or Cs(2)CO(3)-mediated conditions at room temperature, is described. A comparable diethyl fluoro(naphthalen-2-yl)methylphosphonate reagent does not react with paraformaldehyde under these mild conditions. The utility of the methodology for synthesis of terminal α-fluoroalkenes bearing electron-withdrawing functionalities is also shown.