- An Improved Synthesis of 3,6-Dihydro- as -indacene
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This contribution describes an updated synthetic route to 3,6-dihydro- as -indacene along with full characterization of all inter mediates. The title compound is prepared by Mannich condensation of 2-methylfuran with formaldehyde and dimethylamine hydrochloride, quaternization of the resulting amine with methyl iodide, and conversion into the ammonium hydroxide salt by treatment with silver oxide in water. Subsequent Hoffmann elimination and [6,6]-cycloaddition through pyrolysis produces a furanocyclophane, which after photooxidation, intramolecular cycloaddition, and dehydration with sodium carbonate affords 2,3,6,7-tetrahydro-1,8-dione- as -indacene. Reduction of this diketone gives a mixture of alcohols, which after dehydration under slightly basic or acidic conditions produces 3,6-dihydro- as -indacene. The structure is confirmed by X-ray diffraction, and all intermediates are characterized by means of 1H and 13C NMR spectroscopy.
- Dibdalli, Yuvaraja,Faúndez, Rodrigo,Preite, Marcelo,Molins, Elies,Chávez, Ivonne,Amshumali, Mungalimane K.,Morales-Verdejo, Cesar,Manriquez, Juan M.
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p. 569 - 573
(2020/09/18)
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- Oligomerization of the Thiophene-Based p-Quinodimethanes 2,5-dihydrothiophene and 2-Ethylidene-5-methylene-2,5-dihydrothiophene
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Flash vacuum pyrolysis (FVP) of (5-methyl-2-thiophene-yl)methyl benzoate (8) produces in ca. 75% yield 2,5-dimethylene-2,3-dihydrothiophene, S-monomer (3). S-Monomer 3 is relatively stable dissolved in carbon disulfide-chloroform at -78°C. The structure of 3 is confirmed by its spectral properties. When a 0.17 M solution of S-monomer 3 was allowed to warm to room temperature, SS-dimer 5 ([2,2](2,5)thiophenophane, 14.7%), SSS-trimer 7 ([2,2,2](2,5)thiophenophane, 44.3%), and polymer were produced. A small amount ( 1%) of an SSSS-tetramer was detected by GC/MS. The mechanism proposed for the formation of these oligomers involves the combination of two molecules of 3 to give an intermediate diradical (11) that can close to form dimer 5 or react with additional molecules of 3 to form the higher oligomers. Evidence for the trapping of diradical 11 by 2,5-dimethylene-2,5-dihydrofuran (O-monomer 2) was obtained. Co-oligomerization of S-monomer 3 and O-monomer 2 gave four compounds containing the thiophene moiety: OS-dimer 16, SS-dimer 5, OSS-trimer 17, and SSS-trimer 7. Some OO-dimer 4 was produced but no OOO-trimer 6 was observed and only a trace of OOS-trimer 18 was detected. Additional support for the diradical mechanism was obtained from the study of the oligomerization of the methyl derivatives of 3, 2-ethylidene-5-methylene-2,5-dihydrothiophene (10, E and Z isomers), prepared by the FVP of (5-ethyl-2-thiophene-yl)methyl benzoate (9). Oligomerization of 10 gave several dimers and trimers including two acyclic dimers that are accounted for by intramolecular disproportionation.
- Trahanovsky, Walter S.,Miller, Deborah Louise,Wang, Yili
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p. 8980 - 8986
(2007/10/03)
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- NMR studies of bond order in distorted aromatic systems
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The 4JH-C=C-Me coupling constant has been previously established1,2 as a probe of bond order. This has now been used to examine the bond orders of compounds containing severely distorted benzene nuclei. In the case of 3,4-di-tert-butyltoluene, no electronic distortions in the aromatic ring can be detected by this method. A series of moderately to severely distorted paracyclophanes show no perturbation of electronic structure, with the possible exception of 8-methyl[6]paracyclophane, which exhibits a barely significant deviation from unstrained values. These conclusions are supported by the results of SCF-MO calculations.
- Gready, Jill E.,Hambley, Trevor W.,Kakiuchi, Kiyomi,Kobiro, Kazuya,Sternhell, Sever,Tansey, Charles W.,Tobe, Yoshito
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p. 7537 - 7540
(2007/10/02)
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- Fluoride-Induced 1,6-Elimination to p-Quinodimethane. A New Preparative Method for Paracyclophane, (2.5)Furanophane and (2.5)Thiophenophane
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Fluoride anion induced 1,6-elimination of benzyl>trimethylammonium iodide provides a convenient method for preparation of paracyclophane, (2.5)furanophane, and (2.5)thiophenophane.
- Ito, Yoshihiko,Miyata, Satoru,Nakatsuka, Masashi,Saegusa, Takeo
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p. 1043 - 1044
(2007/10/02)
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