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An electrochemical ‘redox-relay’ system has been developed which allows the generation of C-centered radicals. Intermolecular ‘tin-like’ radical reactions can subsequently be conducted under the most benign of conditions. The yields and efficiency of the processes are competitive and even superior in most cases to comparable conditions with tributyltin hydride. The use of air and electricity as the promotor (instead of a tin or other reagent) combined with the aqueous reaction media make this a clean and ‘green’ alternative to these classic C–C bond forming processes., A ‘green’ and high-yielding electrochemical method for performing tin-free, intermolecular radical reactions (the Giese reaction) has been developed.

4-Iodotetrahydropyran (THP)-containing polymers were synthesized via Prins cyclization of monomers with an aldehyde moiety and a homoallylic alcohol moiety. The progress of polymerization was confirmed by NMR and GPC analysis. The deiodination of the THP in the polymer structure was carried out by reductive hydrogenation using AIBN and tributyltin hydride. Thermogravimetric analysis (TGA) was performed for the THP-containing polymers.

The course of the reaction of 2-propargyl-2-(2-carboethoxyvinyl)cyclohexanone with tributyltin hydride and AIBN either neat or in benzene solution is discussed. The structure of the spirocyclic major product is shown to differ from that previously suggested and plausible reaction pathways are presented to account for the outcome. (C) 2000 Elsevier Science Ltd.

This paper is concerned with the effects of adding tin and/or titanium dopant to sodium aluminium hydride for both dehydrogenation and re-hydrogenation reactions during their reversible storage of molecular hydrogen. Temperature programmed decomposition (TPD) measurements show that the dehydrogenation kinetics of NaAlH4 are significantly enhanced upon doping the material with 2 mol% of tributyltin hydride, Sn(Bu)3H but the tin catalyst dopant is shown to be inferior than titanium. On the other hand, in this preliminary work, a significant synergetic catalytic effect is clearly revealed in material co-doped with both titanium and tin catalysts which shows the highest reversible rates of dehydrogenation and re-hydrogenation (after their hydrogen depletion). The re-hydrogenation rates of depleted Sn/Ti/NaAlH4 evaluated at both 9.5 and 140 bars hydrogen are also found to be favourable compared to the Ti/NaAlH4, which clearly suggest the importance of the catalyst choice. Basing on these results some mechanistic insights for the catalytic reversible dehydrogenation and re-hydrogenation processes of Sn/Ti/NaAlH4 are therefore made. © 2006 Elsevier Ltd. All rights reserved.

Thirteen difluoromethyl-containing pseudopeptides were synthesized by Ugi reaction using the novel building block 2,2-difluoro-2-(phenylthio)acetic acid (2) as one component, followed by removal of the phenylsulfanyl protecting group in the presence of tributyltin hydride and azobisisobutyronitrile.

This article describes two convenient methods for removing the ω-terminal bromine atom of well-defined soluble polymer supports prepared by atom transfer radical polymerization (ATRP). The targeted soluble supports are linear polystyrene chains that contain an acid-labile p-alkoxybenzyl ester linker (i.e. Wang linker) at their α-chain end. These polymers are synthesized by ATRP using a fluorenylmethoxycarbonyl (Fmoc)-protected amino functional ATRP initiator, namely 3-(Fmoc-amino)propyl 2-bromoisobutyrate. After polymerization and before Wang functionalization, the bromine-atom of the ATRP-made soluble supports was removed. Two different debromination approaches were considered. The first one consists in reducing the terminal alkyl bromide in the presence of a trialkyltin hydride. This method can be applied directly in the ATRP medium at the end of the polymerization or can be performed on a purified polymer sample. The latter conditions were found to be more suitable. It was also observed that the use of tributyltin hydride in the absence of additional radical initiator led to the best results. Indeed, well-defined polymer supports with controlled chain-length, molecular weight distribution and fully dehalogenated chain-ends were obtained. The second dehalogenation approach consisted in removing the terminal bromide by nucleophilic substitution with sodium azide. Afterwards, the formed terminal azide group was reacted with 1-pentyne by copper-catalyzed azide-alkyne 1, 3-dipolar Huisgen cycloaddition. This method was also found to be valid for preparing bromine-free polystyrene supports. After ω-chain-end debromination, Fmoc-deprotection was performed on the α-chain-end and the resulting amine function was reacted with 4-(hydroxymethyl)phenoxyacetic acid. Further esterification of the Wang linker is also possible.

Treatment of 1,1,3,3-tetrakis(alkylthio)-2-silapropanes with t-BuLi in THF at -40 °C generated 1,1,3,3-tetrakis(alkylthio)-1,3-dilithio-2-silapropanes which reacted with various bifunctional chlorosilanes to give the corresponding 4- to 7-membered polysilacycloalkanes in moderate to good yields. Furthermore, double alkylation of the dilithiated silanes with bis(halomethyl)diorganosilanes or dihaloalkanes was found to proceed smoothly giving rise to 1,4-disilacyclohexanes or silacycloalkanes in good yields, respectively, in THF and an aprotic polar co-solvent such as hexamethylphosphoric triamide (HMPA) or 1,1,3,3-tetramethylurea (TMU). The sulfenyl groups in the cyclized products were smoothly removed by radical reduction with tributyltin hydride.

Tri(2-furyl)germane is a readily prepared, easy-to-handle, and storable triorganogermane. The three 2-furyl groups confer unique reactivity on it in a variety of reactions. Tri(2-furyl)germane is a promising alternative to tributyltin hydride in radical reaction, especially superior in radical addition to alkenes. The hydrogen of tri(2-furyl)germane is so acidic that generation of the corresponding germyl anion is achieved with the aid of weak bases, such as potassium tert-butoxide and cesium carbonate. The anion participates in nucleophilic addition to aldehydes, 1,4-addition to α,β-unsaturated carbonyl compounds, and coupling reaction with aryl and vinyl halides under palladium catalysis. Palladium-catalyzed hydrogermylation with tri(2-furyl)germane create some novel phenomena. Some chemistry of triphenylgermane will be described.

The preparation of 3-substituted tetrahydropyrazinoisoquinolines using the tributyltin hydride mediated intramolecular radical cyclization of suitably protected 2-substituted 3,4-dihydropyrazines is reported. The compounds are obtained as single enantiomers, as the relative configuration of the new generated stereogenic center is driven by the stereochemistry of the 2-substituted carbon in the starting materials, which is in turn derived from naturally occurring amino acids.

Starting from (+)-3-carene 1 several spirolactones with carane backbone were synthesized. δ-Hydroxy-γ-lactone 5 was obtained by acidic lactonization of a γ,δ-epoxy ester. Iodolactone 8 and bromolactone 9 were products of iodolactonization of γ,δ-unsaturated acid 7 and bromolactonization of γ,δ-unsaturated ester 3 respectively. The halo lactones were subjected to reductive dehalogenation with tributyltin hydride and dehydrohalogenation with DBU. The structures of the lactones obtained were confirmed by X-ray analysis and spectral data.

This manuscript describes the selective synthesis of2, 4-bis(trifluoromethyl)phenylphosphinic acid, (Rf)P(O)(H)OH.Reaction of chlorobis(diethylamino)phosphane with a mixture of 2, 4-(CF3)2C6H3Li and 2, 6-(CF3)2C6H3Li results in the formation of 2, 4-bis(trifluoromethyl)phenylbis(diethylamino)phosphane, (Rf)P(NEt2)2. The following in situ reaction with gaseous HBr leads to the cleavage of the phosphorus nitrogen bonds resulting in the selective formation of the corresponding dibromophosphane (Rf)PBr2.2, 4-Bis(trifluoromethyl)phenylphosphinic acid is available via two different synthetic strategies starting from the dibromophosphane (Rf)PBr2. Reduction of the dibromophosphane with tributyltin hydride affords selectively the phosphane (Rf)PH2. The following oxidation to the phosphinic acid (Rf)P(O)(H)OH, however, only proceeds in moderate yields. A more efficient synthesis is achieved via the hydrolysis of the dibromophosphane (Rf)PBr2 in dichloromethane solution. 2, 4-bis(trifluoromethyl)phenylphosphinic acid, (Rf)P(O)(H)OH, is surprisingly stable towards air and water. The water soluble phosphinic acid reacts sluggishly with a 30?% H2O2 solution, yielding only 23?% of the corresponding phosphonic acid (Rf)P(O)(OH)2 after seven days at ambient temperature.In principle a tautomerization of the phosphinic acid (Rf)P(O)(H)OH to the corresponding phosphonous acid (Rf)P(OH)2 analogously to the phosphane oxide (Rf)2P(O)H and the phosphinous acid (Rf)2POH is conceivable. However, the phosphonous acid could not be detected with spectroscopic methods. The energy difference between the phosphinic acid and the phosphonous acid is calculated by quantum chemical calculations at the B3LYP/6-311+G(2df, p) level of theory to 30.1 kJ.mol1. This high value explains why the phosphonous acid tautomer could not be detected by spectroscopic methods so far.As transition metal complexes featuring phosphonous acid ligands are of significant interest for the application as homogeneous catalysts we studied the coordination chemistry of the related phosphinic acid in more detail. The preligand 2, 4-bis(trifluoromethyl)phenylphosphinic acid reacts smoothly with palladium dichloride in THF to the dinuclear complex [Pd2(mu-Cl)2{[2, 4-(CF3)2C6H3P(OH)O]2H}2], featuring a phosphonous acid phosphonato unit, with a strong hydrogen bridge substantiated by an O center dot center dot center dot O distance of 247.7(3) pm. The dinuclear phosphonous acid palladium complex exhibits a high catalytic activity in the Suzuki cross-coupling. Alternatively, the phosphinic acid can be used as preligand for the in situ formation of a phosphonous acid palladium complex. These compounds combine catalytic activity with a very high stability towards air and water.

Tributyltin hydride in N -methyl-2-pyrrolidinone (NMP)was used for the partial reduction of various functionalized acidchlorides at room temperature. This transition-metal-free procedureallows the synthesis of a range of (hetero)aromatic- and aliphatic al-dehydes in good to excellent yields. Key words: acid chlorides, aldehydes, reduction, tributyltin hy-dride, N -methyl-2-pyrrolidinone, free-metal conditions The partial reduction of acid chlorides to aldehydes seemsto be a simple reaction, yet this type of transformation re-mains a desirable tool. Over the past decades, a variety ofmethods have been developed. Besides the traditional hy-drogenolysis with Pd/BaSO 4 (Rosenmund reduction), 1 many metallic hydrides have been extensively used forsuch transformations, including, lithium or sodium tri- t -butoxyaluminium hydride, 2 sodium borohydride, 3 hyper-valent silicon hydrides, 4 transition-metal borohydrides, 5 anionic transition-metal reductants, 6 and others. 7 Howev-er, such methods have limitations, which include over-reduction, lack of generality, low yield and functionalgroup incompatibility. Alternative methods involve theuse of organosilicon

Radical-based carbonylation reactions of alkyl halides were conducted in a microflow reactor under pressurized carbon monoxide gas. Good to excellent yields of carbonylated products were obtained via radical formylation, carbonylative cyclization and three-component coupling reactions, using tributyltin hydride or TTMSS as a radical mediator.

Regioselectively fluoro-, trifluoromethyl- and trifluoromethoxy-substituted 3-methyleneindolines have been prepared using a four-step procedure involving metalation/bromination of fluorinated Boc-protected anilines, N -propargylation of the resulting o -bromoarylcarbamate and reductive radical cyclization of the product with tributyltin hydride/AIBN. 3-Methyleneindolines, as valuable, versatile intermediates, can be transformed into highly functionalized 3-substituted indoles by ene-type reactions using different enophiles. Thus, fluoro-, trifluoromethyl- and trifluoromethoxy-substituted diethyl 2-hydroxy-2-[(1 H -indol-3-yl)methyl]malonates, ethyl 2-hydroxy-3-(1 H -indol-3-yl)propionates and ethyl 2-hydroxy-3-(1 H -indol-3-yl)-2-trifluormethylpropionates were obtained in 77–86% yield by simply heating the corresponding tert -butyl 3-methyleneindoline-1-carboxylate with an equimolar amount of diethyl ketomalonate, ethyl glyoxalate and ethyl 3,3,3-trifluoropyruvate, respectively, at 100 °C, without solvent, for 0.5–4 h.

This paper describes the screening of 22 extracts from 18 different aquatic environmental samples for androgenic activity, including indirect and interactive effects on androgen receptor (AR)-mediated signal transduction, using the AR-LUX bioassay. Four samples, originating from an industrial wastewater treatment plant (WTP) or the river Meuse, were shown to contain substantial androgenic activity. Moreover, the samples originating from the industrial WTP showed an enhancement of the maximal androgenic response relative to that elicited by the standard androgen methyltrienolone (R1881) in the AR-LUX assay. This indicates the involvement of cellular mechanisms other than receptor-ligand interaction influencing AR-regulated pathways. This also demonstrates the additional value of cell based assays featuring a more complete array of fully functional interacting pathways. Chemical analysis using GC-MS confirmed the presence of a number of androgens and also estrogens in these WTP samples. Subsequently, we showed that estrone and tributyltin hydride (TBT-H) enhance the response to androgens. This indicates that the presence of numerous compounds in addition to androgens in environmental mixtures might very well result in a more profound perturbation of the normal physiology of exposed organisms than estimated based on the androgen levels alone. Therefore, risk assessment of environmental samples should include an evaluation of the presence and the interactive effects of (ant)agonists of carefully selected relevant cellular receptors in order to provide a realistic estimate of the integrated ecotoxicological risk of the compounds present. © 2004 Elsevier B.V. All rights reserved.

This paper describes the screening of 22 extracts from 18 different aquatic environmental samples for androgenic activity, including indirect and interactive effects on androgen receptor (AR)-mediated signal transduction, using the AR-LUX bioassay. Four samples, originating from an industrial wastewater treatment plant (WTP) or the river Meuse, were shown to contain substantial androgenic activity. Moreover, the samples originating from the industrial WTP showed an enhancement of the maximal androgenic response relative to that elicited by the standard androgen methyltrienolone (R1881) in the AR-LUX assay. This indicates the involvement of cellular mechanisms other than receptor-ligand interaction influencing AR-regulated pathways. This also demonstrates the additional value of cell based assays featuring a more complete array of fully functional interacting pathways. Chemical analysis using GC-MS confirmed the presence of a number of androgens and also estrogens in these WTP samples. Subsequently, we showed that estrone and tributyltin hydride (TBT-H) enhance the response to androgens. This indicates that the presence of numerous compounds in addition to androgens in environmental mixtures might very well result in a more profound perturbation of the normal physiology of exposed organisms than estimated based on the androgen levels alone. Therefore, risk assessment of environmental samples should include an evaluation of the presence and the interactive effects of (ant)agonists of carefully selected relevant cellular receptors in order to provide a realistic estimate of the integrated ecotoxicological risk of the compounds present. (C) 2004 Elsevier B.V. All rights reserved.

Thermal reaction of various alpha-azido esters with Bu(3)SnH in refluxing benzene results in smooth production of 3-(tributylstannyl)-1-triazene adducts affording cyclized 1,2,3-triazol-4-ones in preference to reduced amines and thence provides a new useful method for the preparation of these triazole derivatives. In the presence of AIBN the occurrence of triazene products still remains important or even exclusive and, consequently, generation of the expected stannylaminyl radicals is seriously limited. With 2-azidomalonates and alpha-azido-beta-keto esters stannyltriazenes can similarly occur in the absence of the radical initiator, but in the latter cases the ensuing triazenes undergo preferential cyclization onto the ketone moiety to give reactive hydroxytriazolines. Contrary to alpha-azido esters, in the presence of AIBN alpha-azido-beta-keto esters as well as azidomalonates give rise only to the usual stannylaminyl radicals. A possible explanation for the different behavior of the mono- and dicarbonyl azides in the presence of AIBN is put forward.

The radical reaction of tributyltin hydride with azidoalkylmalononitriles bearing variously substituted alkenyl groups gives rise to pyrrolopyrroles and pyrrolopyridines through tandem cyclization reaction of initial stannylaminyl radicals onto either nitrile group followed by cyclization of ensuing aminoiminyl radicals onto the alkenylic moiety