- Cope Rearrangement in the Thiophene Series
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The inability to observe Cope rearrangement at elevated temperature for diethyl α-allylphenylmalonate does not extend to the analogous systems resulting from replacement of the benzene ring by 2- and 3-thiophene nuclei.Thermal rearrangement of diethyl α-allyl-2-thienylmalonate (5) at 250-260 deg C for 12 h produces the expected Cope rearrangement product diethyl (3-allyl-2-thienyl)malonate (6) (49percent) accompanied by ethyl 6-carboethoxy-5,6-dihydro-4H-5-cyclopentathiopheneacetate (7) (28percent).The structural verification of 6 was obtained by degradation to 3-allyl-2-methylthiophene which was compared with an authentic sample obtained by synthesis.The structure of 7 was based on analogy.Similar results were observed with the 3-substituted analogues of 5, both diethyl (2-allyl-3-thienyl)malonate (14) and ethyl 4-carboethoxy-5,6-dihydro-4H-5-cyclopentathiopheneacetate (15) being formed.In this case the structure of 14 was verified by synthesis.Speculative mechanistic considerations are offered regarding the mode of transformation of 6 to 7 and 14 to 15.That the methine proton of the malonate substituent in 6 and 14 is involved in this transformation is seen by the inability of the appropriate methyl-substituted derivative of 6 to undergo thermal cyclization.
- MacDowell, Denis W. H.,Purpura, Joseph M.
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Read Online
- Synthesis, X-ray crystallographic analysis, and theoretical structure analysis of tetrathienylethenes designed for photo- and electrochromism
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As part of an effort to develop a new chromic system that responds to both photoexcitation and electron transfer, tetrakis(2-methylthien-3-yl)ethene (3a) and its tetrakismethylthio derivative (3b) were synthesized. The results of X-ray crystallographic and theoretical analyses of these substances suggest that (1) conformers of 3 with an antiparallel arrangement of two vicinal thienyl groups will undergo photocyclization, and (2) the most stable conformer of 3 having an anti-double parallel conformation will not. These predictions were preliminarily confirmed by the results of photochemical and cyclic voltammetry studies.
- Ikeda, Hiroshi,Sakai, Azusa,Namai, Hayato,Kawabe, Akinori,Mizuno, Kazuhiko
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Read Online
- Remarkably Efficient Iridium Catalysts for Directed C(sp2)-H and C(sp3)-H Borylation of Diverse Classes of Substrates
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Here we describe the discovery of a new class of C-H borylation catalysts and their use for regioselective C-H borylation of aromatic, heteroaromatic, and aliphatic systems. The new catalysts have Ir-C(thienyl) or Ir-C(furyl) anionic ligands instead of the diamine-type neutral chelating ligands used in the standard C-H borylation conditions. It is reported that the employment of these newly discovered catalysts show excellent reactivity and ortho-selectivity for diverse classes of aromatic substrates with high isolated yields. Moreover, the catalysts proved to be efficient for a wide number of aliphatic substrates for selective C(sp3)-H bond borylations. Heterocyclic molecules are selectively borylated using the inherently elevated reactivity of the C-H bonds. A number of late-stage C-H functionalization have been described using the same catalysts. Furthermore, we show that one of the catalysts could be used even in open air for the C(sp2)-H and C(sp3)-H borylations enabling the method more general. Preliminary mechanistic studies suggest that the active catalytic intermediate is the Ir(bis)boryl complex, and the attached ligand acts as bidentate ligand. Collectively, this study underlines the discovery of new class of C-H borylation catalysts that should find wide application in the context of C-H functionalization chemistry.
- Chattopadhyay, Buddhadeb,Hassan, Mirja Md Mahamudul,Hoque, Md Emdadul
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supporting information
p. 5022 - 5037
(2021/05/04)
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- Mild-Base-Promoted Arylation of (Hetero)Arenes with Anilines
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Transition metal-free radical arylation of heteroarenes is achieved at room temperature by simply adding aqueous sodium carbonate to a solution of the corresponding heteroarene and arenediazonium salt, which can even be formed in situ. Such an easy, inexpensive and mild methodology has been optimized and applied to the expeditious modification of interesting molecular cores like naphthylimide or bisthienylcyclopentenes.
- Monzón, Diego M.,Santos, Tanausú,Pinacho-Crisóstomo,Martín, Víctor S.,Carrillo, Romen
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p. 325 - 333
(2018/01/15)
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- Practical preparation of ethyl 2-methylthiophene-3-carboxylate
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A safe and efficient process for the preparation of ethyl 2-methylthiophene-3-carboxylate (5) was devised. This process provides several advantages over the precedents, involving operational simplicity, avoidance of the use of strong bases such as n-butyllithium and application of noncryogenic conditions, and enabled to prepare 5 in 52% overall yield from commercially available 2-methylthiophene on a multikilogram scale.
- Kogami, Masakazu,Watanabe, Nobuhide
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experimental part
p. 797 - 798
(2011/07/29)
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- PROCESS FOR THE PRODUCTION OF INTERMADIATES FOR THE PREPARATION OF TRICYCLIC BENZIMIDAZOLES
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The invention relates to a process for the synthesis of compounds of the formula 1-a and compounds of the formula 1-b. The compounds of the formula 1-a and the compounds of the formula 1-b, in which the substituents R1, R2, R3, and Ar have the meanings indicated in the description, are valuable intermediates for the preparation of pharmaceutically active compounds.
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Page/Page column 99
(2010/11/25)
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- Polycyclic fused heteroring compounds metal complexes and polymerization process
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Metal complexes comprising a polycyclic, heteroatom containing fused ring compound comprising at least a cyclopentadienyl ring having fused thereto a 5-membered polyatomic ring containing one or more ring atoms selected from groups 15 or 16 of the Periodic Table of the Elements and lacking substituents forming 6-membered, aromatic fused rings; polymerization catalysts; and olefin polymerization processes using the same are disclosed.
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- Bistable photoswitching in the film of fluorescent photochromic polymer: Enhanced fluorescence emission and its high contrast switching
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The synthesis of aggregation-induced enhanced emission (AIEE)-based fluoroscent photochromic polymer, poly(DCS-BTE), whose strong fluorescence in the neat polymer film could photoswitched, was discussed. Polymeric film consisting of DCS in PMMA matrix were fabricated by spin-coating. Molecular planarization and J-type aggregation were observed in the DCS molecules gated by the specific intermolecular interactions in the solid state. The results show that the erasable fluorescence photoimaging on the spin-coated poly(DCS-BTE) film is successfully demonstrated.
- Lim, Seon-Jeong,An, Byeong-Kwan,Park, Soo Young
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p. 6236 - 6239
(2008/02/02)
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- Photoswitchable organic nanoparticles and a polymer film employing multifunctional molecules with enhanced fluorescence emission and bistable photochromism
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Get turned on: Fluorescent photochromic organic nanoparticles (FPONs) of 1 (see picture) show a strongly enhanced fluorescence emission with increasing concentration and bistable photochromism. High-contrast on/off fluorescence switching has been successfully implemented in size-tuned FPONs of 1 and also in a photo-rewritable polymer film highly loaded with 1. (Chemical equation presented).
- Lim, Seon-Jeong,An, Byeong-Kwan,Sang, Don Jung,Chung, Myung-Ae,Soo, Young Park
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p. 6346 - 6350
(2007/10/03)
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- Metallocene compounds, process for their preparation and their use in catalytic systems for the polymerization of olefins
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A class of metallocene compounds is disclosed having general formula (I) wherein Y is a moiety of formula (II) wherein A, B, and D, same or different from each other, are selected from an element of the groups 14 to 16 of the Periodic Table of the Elements (new IUPAC version), with the exclusion of nitrogen and oxygen; R1, R2, R3, R4and R5are hydrogen or hydrocarbon groups, Z is selected from a moiety of formula (II) as described above and from a moiety of formula (III) wherein R6, R7, R8and R9, are hydrogen or hydrocarbon groups; L is a divalent bridging group; M is an atom of a transition metal selected from those belonging to group 3, 4, 5, 6 or to the lanthanide or actinide groups in the Periodic Table of the Elements (new IUPAC version), X, same or different, is hydrogen, a halogen, a R10, OR10, OSO2CF3, OCOR10, SR10, NR102or PR102group, wherein the substituents R10are hydrogen or alkyl groups; p is an integer of from 1 to 3, being equal to the oxidation state of the metal M minus 2. The above metallocenes are particularly useful in the polymerization of propylene.
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- Metallocene compounds, process for their preparation and their use in catalytic systems for the polymerization of olefins
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A class of metallocene compounds is disclosed having the general formula (I): wherein Y is a moiety of formula (II) wherein A, B and D, same or different from each other, are selected from an element of the groups 14 to 16 of the Periodic Table of the Elements (new IUPAC version), with the exclusion of nitrogen and oxygen; R1, R2, R3, R4and R5are hydrogen or hydrocarbon groups, Z is selected from a moiety of formula (II) as described above and from a moiety of formula (III): wherein R6, R7, R8and R9, are hydrogen or hydrocarbon groups; L is a divalent bridging group; M is an atom of a transition metal selected from those belonging to group 3, 4, 5, 6 or to the lanthanide or actinide groups in the Periodic Table of the Elements (new IUPAC version), X, same or different, is hydrogen, a halogen, a R10, OR10, OSO2CF3, OCOR10, SR10, NR102or PR102group, wherein the substituents R10are hydrogen or alkyl groups; p is an integer of from 0 to 3, being equal to the oxidation state of the metal M minus 2. The above metallocenes are particular useful in the polymerization of propylene.
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- Chiral ansa metallocenes with Cp ring-fused to thiophenes and pyrroles: Syntheses, crystal structures, and isotactic polypropylene catalysts
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Syntheses, crystal structures, and polymerization data for new isospecific metallocenes (heterocenes) having cyclopentenyl ligands b-fused to substituted thiophenes (Tp) and pyrroles (Pyr) are reported. The C2and C1-symmetric heterocenes are dimethylsilyl bridged, have methyl groups adjacent to the bridgehead carbon atoms, and have aryl substituents protruding in the front. rac-Me2Si(2,5-Me2-3-Ph-6-Cp [b]Tp)2ZrCl2/MAO (MAO = methyl alumoxanes) is the most active metallocene catalyst for polypropylene reported to date. rac-Me2Si (2,5-Me2-3-Ph-6-Cp[b]Tp)2ZrCl2 and rac-Me2Si (2,5-Me2-1-Ph-4-Cp[b]Pyr)2ZrCl2 have the same structure, and the former is 6 times more active, produces half the total enantiofacial errors, and is 3.5 times less regiospecific in propylene polymerizations at the same conditions. rac-Me2Si(2-Me-4-Ph-1-Ind)2ZrCl2/ MAO is 3.5 times lower in activity than rac-Me2Si(2,5-Me2-3-Ph-6-Cp[b] Tp)2ZrCl2 catalyst, and while the former is the more stereospecific and the less regiospecific, the sum of these two enantioface errors is the same for both species. Fine-tuning the heterocene sterics by changing selected hydrogen atoms on the ligands to methyl groups influenced their catalyst activities, stereospecificites, regiospecificites, and isotactic polypropylene (IPP) Mw. Thus, both substituting a hydrogen atom adjacent to the phenyl ring with a methyl group on an azapentalenyl ligand system and replacing one and then two hydrogens on the phenyl ring with methyls on thiopentalenyl ligands provided increased polymer Tm and Mw with increasing ligand bulk. Polymer molecular weights are sensitive to and inversely proportional to MAO concentration, and the catalyst activities increase when hydrogen is added for molecular weight control. The polymer Tm values with the thiopentalenyls as TIBAL/[Ph3C][B(C6F5)4] systems were higher than with MAO as catalyst activator. A racemic C1, pseudomeso complex with a hybrid dimethylsilyl-bridged 2-Me-4-Ph-1 1-Ind/2,5-Me2-4-Ph-1-Cp[b]Pyr ligand produced the first sample of IPP with all the steric pentad intensities fitting the enantiomorphic site control model. Speculative mechanistic considerations are offered regarding electronic effects of the heteroatoms and steric effects of the ligand structures, the preferred phenyl torsion angles, and anion effects.
- Ewen,Elder,Jones,Rheingold,Liable-Sands,Sommer
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p. 4763 - 4773
(2007/10/03)
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- Compounds useful for the inhibition of the replication of HIV-1 and HIV-1 mutants
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Compounds of the formula STR1 wherein X is O or S, useful for the inhibition of the replication of HIV-1 and reverse transcriptase mutants thereof, in vitro and in vivo.
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- Structure-Odor Correlation, XXI. Olfactory Properties and Convenient Synthesis of Furans and Thiophenes Related to Rose Furan and Perillene and Their Isomers
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Starting from 3-bromofuran (1) or 3-bromothiophene (2) via alkylation in 2-position (-> 3-8) followed by the corresponding second alkylation in 3-position, we obtained rose furan (9), rose thiophene (10), and their analogs 11-16.From the α,β-unsaturated esters 17-20 by hydrogenation (-> 21-24), DIBAH reduction (-> 25-28), and Wittig reaction, perillene (29), thioperillene (30), and their analogs 29-36 were obtained.Olfactory evaluation showed that the difference between the furans and thiophene derivatives is remarkably small, particularly for perillene (29) compared with thioperillene (30), and their analogs.Also the influence of position and structure of the side chain is lower than expected within the compared compounds 9-36. - Keywords: Rose furan / Perillene / Furans / Thiophenes / Structure-odor correlation / Odoriferous substances
- Weyerstahl, Peter,Schenk, Anja,Marschall, Helga
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p. 1849 - 1854
(2007/10/03)
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- Evaluation of the Key Odorants in a Thermally Treated Solution of Ribose and Cysteine by Aroma Extract Dilution Techniques
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Application of the aroma extract dilution analysis on a solvent extract isolated from a thermally treated solution (145 deg C; 20 min) of cysteine/ribose led to the identification of 2-furfurylthiol, 3-mercapto-2-pentanone, 2-methyl-3-furanthiol, 5-acetyl-2,3-dihydro-1,4-thiazine, 3-mercapto-2-butanone, and bis(2-methyl-3-furyl) disulfide showing the highest flavor dilution factors among the 29 odor-active volatiles.HRGC/olfactometry of decreasing headspace volumes established especially 2-furfurylthiol and 2-methyl-3-furanthiol as important odorants and revealed 2-thenyl mercaptan and ethyl mercaptan as further key contributors to the overall roasty, meatlike, sulfury odor of the model mixture. 5-acetyl-2,3-dihydro-1,4-thiazine, identified for the first time among the volatiles of Maillard model reactions or foods, exhibited an intense roasty, popcorn-like odor at the low odor threshold of 0.06 ng/L of air, which was of the same order of magnitude as those reported in the literature for the roasty-smelling odorants 2-acetyl-1-pyrroline and 2-acetyl-2-thiazoline.Keywords: Aroma extract dilution analysis; nonenzymatic browning; Maillard reaction; ribose; cysteine; flavor; 5-acetyl-2,3-dihydro-1,4-thiazine
- Hofmann, Thomas,Schieberle, Peter
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p. 2187 - 2194
(2007/10/02)
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- Thiophene Oligomers with a Photoswitch
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Thiophene oligomers having a dithienylethene structure show large shifts in oxidation potential to the cathodic region in excess of 0.87 - 1.27 V by photocyclization.
- Saika, Tetsuyuki,Irie, Masahiro,Shimidzu, Takeo
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p. 2123 - 2124
(2007/10/02)
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- A simple and improved procedure for selective ring bromination of alkyl-substituted aromatic hydrocarbons on the surface of alumina
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Highly selective ring bromination of alkyl-substituted aromatic hydrocarbons has been achieved using molecular bromine adsorbed on the surface of alumina without any solvent.
- Ranu,Sarkar,Chakraborty
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p. 1095 - 1099
(2007/10/02)
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