- Orthogonal Stability and Reactivity of Aryl Germanes Enables Rapid and Selective (Multi)Halogenations
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While halogenation is of key importance in synthesis and radioimaging, the currently available repertoire is largely designed to introduce a single halogen per molecule. This report makes the selective introduction of several different halogens accessible. Showcased here is the privileged stability of nontoxic aryl germanes under harsh fluorination conditions (that allow selective fluorination in their presence), while displaying superior reactivity and functional-group tolerance in electrophilic iodinations and brominations, outcompeting silanes or boronic esters under rapid and additive-free conditions. Mechanistic experiments and computational studies suggest a concerted electrophilic aromatic substitution as the underlying mechanism.
- Deckers, Kristina,Fricke, Christoph,Schoenebeck, Franziska
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supporting information
p. 18717 - 18722
(2020/08/25)
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- Multimetallic Ni- and Pd-Catalyzed Cross-Electrophile Coupling to Form Highly Substituted 1,3-Dienes
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The synthesis of highly substituted 1,3-dienes from the coupling of vinyl bromides with vinyl triflates is reported for the first time. The coupling is catalyzed by a combination of (5,5′-bis(trifluoromethyl)-2,2′-bipyridine)NiBr2 and (1,3-bis(diphenylphosphino)propane)PdCl2 in the presence of a zinc reductant. This method affords tetra- and penta-substituted 1,3-dienes that would otherwise be difficult to access and tolerates electron-rich and -poor substituents, heterocycles, an aryl bromide, and a pinacol boronate ester. Mechanistically, the reaction appears to proceed by an unusual zinc-mediated transfer of a vinyl group between the nickel and palladium centers.
- Olivares, Astrid M.,Weix, Daniel J.
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supporting information
p. 2446 - 2449
(2018/02/28)
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- Sterics vs electronics: Revisiting the catalytic regioselective hydrodebromination of 2,3,5-tribromothiophene
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The application of sterically hindered palladium catalysts to the regioselective hydrodebromination of 2,3,5-tribromothiophene has been studied in detail, including the effects of catalyst choice, solvent, reaction time, and temperature, as well as the method of NaBH4 addition and the role of chelating additives to effect NaBH4 solubility. Ultimately it was determined that the background reaction between NaBH4 and bromothiophenes is too facile to allow both total conversion and high selectivity. Optimized conditions finally allowed a selectivity of ca. 16:1 with overall conversion of 100%. However, complications of overdebromination under these conditions still limit the yield of the desired 2,3-dibromothiophene to 65%.
- Konkol, Kristine L.,Rasmussen, Seth C.
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supporting information
p. 3234 - 3239
(2016/10/09)
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- Synthesis of poly(thiophene-alt-pyrrole) from a difunctionalized thienylpyrrole by Kumada polycondensation
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A difunctional thienylpyrrole monomer with a bromide on the thienyl moiety and a magnesium halide on the pyrrole moiety was prepared via chemo-selective magnesium-iodine exchange. Based on this monomer, a π-conjugated alternating poly(thiophene-alt-pyrrole) PTP was synthesized via nickel and palladium catalyzed Kumada polycondensation. The optical and thermal properties of this polymer have been investigated and suggested a wide band gap polymer, with a very low Tg for such polymers.
- He, Lu-Ying,Urrego-Riveros, Sara,Gates, Paul J.,N?ther, Christian,Brinkmann, Maren,Abetz, Volker,Staubitz, Anne
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supporting information
p. 5399 - 5406
(2015/07/15)
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- Enatioselective Chalcogeno-Baylis-Hillman reaction of arylaldehydes with MVK and acrylates catalyzed by chiral thiepin-TiCl4 complex
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In a rational chiral molecular design of chalcogenides, optically active thiepin with C2-symmetric chirality was synthesized from commercially available thiophene. Then enatioselective Chalcogeno-Baylis-Hillman reactions of arylaldehydes with methyl vinyl ketone (MVK) and acrylates were investigated in the presence of thiepin-Lewis acid complex. Finally, up to 64% ee was achieved in the presence of 0.2 equiv. of (S)-thiepin at 20°C. Enatioselective Chalcogeno-Baylis-Hillman reactions between benzaldehydes and acrylates were investigated in the presence of chiral thiepin-Lewis acid complex. Finally, up to 64% ee was achieved in the presence of 0.2 equiv. of (S)-thiepin at 20°C. Copyright
- Yin, Yan,Sun, Guofeng,Zhang, Heng,Zhou, Hong,Wu, Fanhong
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p. 365 - 369
(2014/05/20)
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- Dual selectivity: Electrophile and nucleophile selective cross-coupling reactions on a single aromatic substrate
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The development of a high yielding, both nucleophile and electrophile selective cross-coupling reaction with aromatic rings is presented. The reaction is general with respect to functional groups. Furthermore, the products still contain a boronic ester and a bromide. These two functional groups allow them to be easy-to-prepare, highly complex starting materials for further reactions, avoiding protecting group transformations.
- Heinrich, Annika C. J.,Thiedemann, Birk,Gates, Paul J.,Staubitz, Anne
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supporting information
p. 4666 - 4669
(2013/10/08)
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- Design, synthesis, and fungicidal activity of novel analogues of pyrrolnitrin
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A series of novel analogues of pyrrolnitrin containing a thiophene moiety were designed and synthesized by a facile method, and their structures were characterized by 1H nuclear magnetic resonance (NMR) and high-resolution mass spectrometry. The isomers IV-h and V-h were isolated, and their structures were identified by 2D NMR, including heteronuclear multiple-quantum coherence (HMQC), heteronuclear multiple-bond correlation (HMBC), and nuclear Overhauser effect spectrometry (NOESY) spectra. Their fungicidal activities against five fungi were evaluated, and the results indicated that some of the title compounds showed excellent fungicidal activities in vitro against Alternaria solani, Gibberella zeae, Physalospora piricola, Fusarium omysporum, and Cercospora arachidicola at the dosage of 50 μg mL-1. Some compounds shown moderate activity at low dosage. Compound V-h could be considered as a leading structure for further design of agricultural fungicides.
- Wang, Ming-Zhong,Xu, Han,Feng, Qi,Wang, L.I.-Zhong,Wang, S.U.-Hua,Li, Zheng-Ming
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experimental part
p. 7912 - 7918
(2010/09/03)
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- Silver-catalyzed protodecarboxylation of heteroaromatic carboxylic acids
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[Chemical Equation Presented] A simple and highly efficient protodecarboxylation procedure for a variety of heteroaromatic carboxylic acids catalyzed by Ag2CO3 and AcOH in DMSO is described. This methodology can also perform the selective monoprotodecarboxylation of several aromatic dicarboxylic acids.
- Lu, Pengfel,Sanchez, Carolina,Cornella, Josep,Larrosa, Igor
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supporting information; experimental part
p. 5710 - 5713
(2010/02/28)
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- Process for isomerization of 2-halothiophene to 3-halothiophene
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An improved process and catalyst system for the isomerization of halothiophenes. More particularly, an improved process for the isomerization of 2-halothiopehenes to 3-halothiophenes by reacting a 2-halothiophene with a catalyst and in the presence of a base. The addition of a base additive to the acidic zeolite catalyst allows the desired isomerization reaction to take place while suppressing side-reactions that result in the decomposition of thiophene rings. The catalyst lifetime is thus increased and the amount of catalyst needed for the reaction is reduced, lowering cost.
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Page/Page column 3; 4
(2008/06/13)
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- New regiosymmetrical dioxopyrrolo- and dihydropyrrolo-functionalized polythiophenes
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(Chemical Equation Presented) We present the synthesis of two N-alkylated poly(dioxopyrrolothiophene)s and two N-alkylated poly(dihydropyrrolothiophene)s with potential application in the field of conducting polymers. The polymers are synthesized from the corresponding 2,5-dibromothiophenes by an Ullmann-type polymerization and a Stille-type polymerization, respectively. The two N-alkylated poly(dihydropyrrolothiophene)s are the first examples of amino-functionalized polythiophenes built from regiosymmetrical thiophene monomers.
- Nielsen, Christian B.,Bjornholm, Thomas
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p. 3381 - 3384
(2007/10/03)
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- Synthesis of 2,3-Substituted Thienylboronic Acids and Esters
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A noncryogenic protocol for the synthesis of 2-substituted 3-thienylboronic acids and esters as well as 3-substituted 2-thienylboronic acids and esters has been developed. Electrophiles were introduced regiospecifically in the 2-position of 2,3-dibromothiophene and in the 3-position of 2-bromo-3-iodothiophene by halogen-magnesium exchange followed by quenching with electrophiles. Palladium-catalyzed borylation of the 2,3-substituted halothiophenes with pinacolborane and P(t-Bu)3 as ligand for Pd produced 9 and 10. The borylation protocol was tolerated by a range of functional groups; however, strongly electron-withdrawing substituents decreased the stability of the thienylboronic acids and esters.
- Christophersen, Claus,Begtrup, Mikael,Ebdrup, Soren,Petersen, Henning,Vedso, Per
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p. 9513 - 9516
(2007/10/03)
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- Chromium and tungsten carbene complexes of thieno[3,2-b]thiophene
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Dinuclear carbene complexes with 3,6-dimethylthieno[3,2-b] thienylene (T′T′) and thieno[3,2-b]thienylene (TT) spacers were prepared using the classical Fischer method. Their reactivity in solution towards oxygen, as well as their structural features were investigated. Chromium and tungsten carbene complexes were synthesized via dilithiation of the thienothiophene, followed by the addition of the appropriate metal carbonyl complex and subsequent alkylation with triethyloxonium tetrafluoroborate. Monocarbene [M{C(OEt)T′T′H}-(CO)5], (M = Cr, 1; W, 4), biscarbene [(CO)5M{C-(OEt) T′T′C(OEt)}M(CO)5], (M = Cr, 2; W, 5), and the products [M{C(OEt)T′T′C(O)OEt} (CO)5], (M = Cr, 3; W, 6), where a metal moiety of 2 and 5 has been replaced by an ester functionality, were isolated. The reaction product afforded in the reaction of Cr(CO)6 with lithiated thieno[3,2-b]thiophene, [Cr{C(OEt)TTC(O)Bu}(CO)5], 7, did not resemble any of the products isolated in the similar reaction of Cr(CO)6 with lithiated 3,6-dimethylthieno [3,2-b]thiophene.
- Landman, Marile,Goerls, Helmar,Lotz, Simon
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p. 233 - 238
(2007/10/03)
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- Zirconocene catalyzed dehalogenation of aromatic halides by alkylmagnesium reagents
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When aromatic halides were treated with alkylmagnesium reagents (which have β-hydrogens) and a catalytic amount of zirconocene dichloride, dehalogenation proceeded smoothly in high yields. The stoichiometric dehalogenation using dialkylzir-conocenes also proceeded with high selectivities.
- Hara, Ryuichiro,Sun, Wen-Hua,Nishihara, Yasushi,Takahashi, Tamotsu
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p. 1251 - 1252
(2007/10/03)
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- Electrochemical reduction of mono- and dihalothiophenes at carbon cathodes in dimethylformamide. First example of an electrolytically induced halogen dance
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Cyclic voltammetry and controlled-potential electrolysis have been employed to probe the electrochemical reduction of a number of mono- and dihalothiophenes at carbon cathodes in dimethylformamide containing tetramethylammonium perchlorate. Reduction of 2
- Mubarak, Mohammad S.,Peters, Dennis G.
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p. 8074 - 8078
(2007/10/03)
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- Regioselective Debromination of 2,3,5-Tribromothiophene: A Facile Synthesis of Isomerically Pure 2,3- and 2,4-Dibromothiophene
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The regioselective preparative debromination of 2,3,5-tribromothiophene to isomerically pure 2,3- and 2,4-dibromothiophene was effected by the use of sodium borohydride in the presence and absence of transition metal catalyst using predetermined optimum conditions from GC trials.
- Xie, Yang,Ng, Siu-Choon,Hor, T. S. Andy,Chan, Hardy S. O.
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p. 150 - 151
(2007/10/03)
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- ELECTROPHILIC TRICHLOROMETHYLATION OF SOME HALOGENATED THIOPHENES
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The electrophilic trichloromethylation of 3-chloro-, 3-bromo-, and 3,4-dibromothiophene was studied. It is shown that reaction is directed towards position 2, accompanied by frequent formation of the corresponding substituted di-(2-thienyl)dichloromethane. Trichloromethylation of β-bromothiophenes is complicated by exchange of chlorine for bromine under the reaction conditions.
- Gromova, G. P.,Belen'kii, L. I.,Krayushkin, M. M.
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p. 889 - 891
(2007/10/02)
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- A Large-Scale Procedure for the Preparation of 3-Bromothiophene from 2-Bromothiophene and Sodamide in Liquid Ammonia
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3-Bromothiophene can be prepared on a scale of several moles by treatment of 2-bromothiophene with an excess of sodamide in liquid ammonia and subsequent quenching of the reaction mixture with solid ammonium chloride.
- Brandsma, L.,Jong, R.L.P. de
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p. 1697 - 1700
(2007/10/02)
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- Selective Debromination of Thiophene Derivatives by Electrochemical Reduction
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The debromination of polybrominated derivatives is achieved by electrochemical reduction with good yields and high selectivity.
- Dapperheld, S.,Feldhues, M.,Litterer, H.,Sistig, F.,Wegener, P.
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p. 403 - 405
(2007/10/02)
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- Process for preparing thiophene derivatives
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A process for the preparation of a thiophene derivative which is substituted at the beta-position by a bromine atom, which comprises reacting the corresponding beta-unsubstituted thiophene with an aromatic compound which is substituted with a bromine atom, in the presence of an alkali metal amide and a catalyst which is capable of forming a complex with the cation of the alkali metal amide.
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- Process for preparing thiophene derivatives
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A process for the preparation of a thiophene derivative which is substituted at the beta-position by a bromine atom, which comprises reacting the corresponding beta-unsubstituted thiophene with an aromatic compound which is substituted with a bromine atom, in the presence of an alkali metal amide and a catalyst which is capable of forming a complex with the cation of the alkali metal amide.
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- Photochemical Synthesis of Phenyl-2-thienyl Derivatives
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The irradiation (in benzene solution) of 5-bromo- and 5-iodo-thiophene-2-carbaldehyde or the corresponding methyl ketones furnishes the corresponding 5-phenyl derivatives.The same reactivity for other halogenothiophenes is reported: 3,5-dibromothiophene-2-carbaldehyde furnishes the 3-bromo-5-phenyl-2-thienyl derivative while the corresponding di-iodo compound yields 3,5-diphenylthiophene-2-carbaldehyde.In contrast, 5-acetyl-2,3-di-iodothiophene furnishes only the photosubstitution pruduct at C-5.Generally the iodine-containing compounds are more reactive and more stable under the reaction conditions than ones bearing bromine, in agreement with previous reports on the corresponding furan photochemistry.
- Antonioletti, Roberto,Auria, Maurizio D',Onofrio, Franco D',Piancatelli, Giovanni,Scettri, Arrigo
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p. 1755 - 1758
(2007/10/02)
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- The electroreduction of halogenated thiophenes
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Electroreduction of polyhalothiophenes results in the preferential reduction of the α-halogen atoms.Preparative electrochemical reduction of these compounds at controlled potential can be used to synthesize 2,3,4-trihalo, 3,4-dihalo, and 3-halothiophenes.Experimental conditions were developed under which these reductions could be done selectively, giving good yields of the desired products.Electroreduction of tetrabromothiophene can also lead to the formation of a polybromodithyenyl mercury compound.
- Gedye, Richard Neville,Sadana, Yoginder Nath,Leger, Raymond
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p. 2669 - 2672
(2007/10/02)
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- Electrophilic Aromatic Substitution. Part 31. Partial Rate Factors for Detritiation of Thienothiophen and Thienothiophen: Weak Hydrogen Bonding to Sulphur in Trifluoroacetic Acid
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Thienothiophen (I) and thienothiophen (II), specifically labelled with tritium in each position have been prepared, and their rates of protiodetritiation measured along with that for thiophen in either pure trifluoroacetic acid, or mixtures of trifluoroacetic acid and acetic acid, all at 70 deg C.The dependence of exchange rate coefficients upon acid composition indicates that the ring sulphur is hydrogen bonded, and to an extent which depends upon the number of sulphur atoms in the heterocycle.Partial rate factors for detritiation of the non-hydrogen-bonded compounds are calculated as follows (position and compound in parentheses): 7.18E8 ; 6.83E8 ; 9.75E7 (2-thiophen); 7.59E5 ; 5.54E5 ; 7.84E4 (3-thiophen), the corresponding ?+-values being -1.012, -1.010, -0.913, -0.672, -0.656, and -0.560.The results, taken along with those for acylation and chlorination show that (II) is more polarisable than (I), so that these compounds, like all other ?-excessive heterocycles previously examined, are unsuitable for rigorous application of the Extended Selectivity Relationship.Annelation of thiophen by thiophen produces a comparable change in reactivities of the α- and β-positions in contrast to annelation by benzene, where the high resonance energy of benzene plays a crucial role in raising the reactivity of the β-position, relative to that of the α-position.
- Archer, William J.,Roger, Taylor
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p. 295 - 300
(2007/10/02)
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- Preparation of a 3-thienylmalonic acid and the corresponding diesters
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Preparation of a 3-thienylmalonic acid or a diester thereof comprising reacting in a polar solvent in the presence of a copper (I) halide a thiophene compound of formula: STR1 wherein X=I or Br, R1 =H or a C1-4 alkyl group, R2 =H or a C1-2 alkyl group and R3 =H or a C1-2 alkyl group, with the proviso that R2 and R3 cannot be an alkyl group simultaneously, with a mono-deprotonated methylene compound of formula: STR2 wherein a cation is present and Z'=Z" is CN or COOR in which R is a C1-4 alkyl group, or Z'=CN and Z"=COOR' in which R' is a C1-2 alkyl group, followed by hydrolysis by methods known per se to get the corresponding free acid.
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- PROTIODESILYLATION OF SUBSTITUTED 2-TRIMETHYLSILYLTHIOPHENS
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First-order rate constats at 50 deg C have been determined for cleavage of the thiophen compounds XC4H2SSiMe3-2 in mixtures of (a) MeOH (5 vol.) with aqueous HClO4 (2 vol.) and (b) CH3CO2H (4 vol.) with aqueous H2SO4 (3 vol.) Relative rates krel, in the first medium are (X =) 5-OMe, 7 200; 5-Me, 36; H, 1.00; 5-Cl, 1.08E-1; 5-Br, 9.0E-2; 3-Br, 5.0E-2; 4-Br, 4.9E-3, and in the second medium 5-Me, 36; H, 1.00; 5-Cl, 1.28E-1; 5-Br, 9.8E-2; 3-Br, 5.5E-2; 4-Br, 6.5E-3; 5-NO2, 9.1E-7; 3-NO2, 7.1E-7.Except for the nitro-compounds, the two sets of log krel values show excellent linear correlations with values for the corresponding XC6H4SiMe3 compounds, with 3-, 4-, and 5-X in the thiophen ring being taken as equivalent to o-, m-, and p-X groups, respectively, in the benzene ring, the effects of substituents being a litle larger in the thiophen than the benzene system; 3- and 5-O2NC4H2SSiMe3 are less reactive than would be expected from the correlations.Again with the exception of the data for the nitro-compound, the krel values for the 4- and 5- substituted thiophens show very good correlation with ?m+ and ?p+ constants.
- Seconi, Giancarlo,Eaborn, Colin
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p. 931 - 934
(2007/10/02)
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- THE RATES OF BASE CLEAVAGE OF SUBSTITUTED 2-THIENYLTRIMETHYLSILANES. AB INITIO CALCULATIONS OF THE ACIDITIES OF MONOSUBSTITUTED THIOPHENS
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Rates of cleavage in NaOMe-MeOH at 50 deg C have been determined for the mono-substituted 2-trimethylsilylthiophens X*C4H2S*SiMe3-2 with X = H, 3-NO2, 3-Br, 4-Br-, and 5-NO2, -CN, -COPh, -Me, -OMe and -NMe2, and for one disubstituted compound, 4,5-Br2*C4HS*SiMe3-2.For several compounds the rate and product isotope effects have also been determined.The energies involved in the process X*C4H3S X*C4H2S- for deprotonation at the 2-position have been calculated by an ab initio method (STO-3G), and the results used in analysis of the substituent effects in the cleavage of the XC4H2S*SiMe3-2 compounds.The results are consistent with the view the aryl anions separate in the rate-determining step of the cleavage.The isotope effects are all close to unity, whereas by comparison with results for XC6H4CH2SiMe3 and related species of similar reactivity, values in the region of 10 would be expected for the 3- and 5-NO2 compounds if the product isotope effect for a carbanion R depended only in the pKa of RH.The difference between the thienyl- and benzyl-type anions is attributed to the absence of conjugative delocalization of the charge in the former. Approximate pKa values are derived for the 2-positions of the X*C4H3S compounds.
- Seconi, Giancarlo,Eaborn, Colin,Stamper, John G.
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p. 153 - 168
(2007/10/02)
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