- The Missing C1-C5 Cycloaromatization Reaction: Triplet State Antiaromaticity Relief and Self-Terminating Photorelease of Formaldehyde for Synthesis of Fulvenes from Enynes
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The last missing example of the four archetypical cycloaromatizations of enediynes and enynes was discovered by combining a twisted alkene excited state with a new self-terminating path for intramolecular conversion of diradicals into closed-shell products. Photoexcitation of aromatic enynes to a twisted alkene triplet state creates a unique stereoelectronic situation, which is facilitated by the relief of excited state antiaromaticity of the benzene ring. This enables the usually unfavorable 5-endo-trig cyclization and merges it with 5-exo-dig closure. The 1,4-diradical product of the C1-C5 cyclization undergoes internal H atom transfer that is coupled with the fragmentation of an exocyclic C-C bond. This sequence provides efficient access to benzofulvenes from enynes and expands the utility of self-terminating aromatizing enyne cascades to photochemical reactions. The key feature of this self-terminating reaction is that, despite the involvement of radical species in the key cyclization step, no external radical sources or quenchers are needed to provide the products. In these cascades, both radical centers are formed transiently and converted to the closed-shell products via intramolecular H-transfer and C-C bond fragmentation. Furthermore, incorporating C-C bond cleavage into the photochemical self-terminating cyclizations of enynes opens a new way for the use of alkenes as alkyne equivalents in organic synthesis.
- Mohamed, Rana K.,Mondal, Sayantan,Jorner, Kjell,Delgado, Thais Faria,Lobodin, Vladislav V.,Ottosson, Henrik,Alabugin, Igor V.
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supporting information
p. 15441 - 15450
(2015/12/26)
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- Ultrasonicated condensation of indene and 2-nitrofluorene with aromatic aldehydes catalyzed by bis-(p-methoxyphenyl)telluroxide (BMPTO)
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The condensation of indene or 2-nitrofluorene with aromatic aldehydes catalyzed by bis-(p-methoxyphenyl)telluroxide (BMPTO) under ultrasonic wave irradiation gave corresponding fulvenes in fair to good yield.
- Zheng, Ming,Wang, Longcheng,Shao, Jianguo,Zhong, Qi
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p. 1751 - 1755
(2007/10/03)
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- Flow-vacuum pyrolysis of polycyclic compounds. 12: Pyrolysis of 10,11-dihydro-5-methylene-5H-dibenzo[a,d]cycloheptene and of 10,11-dihydro-5-methyl-5H-dibenzo[a,d]cycloheptene
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Flow-vacuum pyrolyses of the title hydrocarbons afford anthracene and 9-methylanthracene as main products. The reaction mechanism suggested by Trahanovsky 2 for pyrolysis of dibenzocyclooctene- and dibenzocycloheptene derivatives is confirmed. For secondary products, parallel radicalic routes are suggested.
- Banciu, Mircea D.,Mangra, Cristina,Petride, Aurica
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p. 565 - 569
(2007/10/03)
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- Addition and cyclization reactions in the thermal conversion of hydrocarbons with an enyne structure, 5: High-temperature ring closures of 1,3-hexadien-5-ynes to naphthalenes - Competing reactions via isoaromatics, alkenylidene carbenes, and vinyl-type radicals
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The 4-substituted 1-phenyl-1-butene-3-ynes 1a-c and the 2-ethynylstyrenes 7a-c were subjected to high-temperature pyrolysis. The cycloisomerization products isolated suggest that these are formed by three competing processes: by (i) an electrocyclic or a molecule-induced, (ii) an alkenylidene carbene controlled, and (iii) a radical-controlled ring-closure . To estimate the relative importance of these three reactions here mentioned, the substrates have been isomerized in oxygen-free nitrogen and in nitrogen proportionally substituted by toluene at 700 and 650°C, respectively. The relative contributions of these isomerizations depend not only on the conversion temperature but also on the substituent R in 1 or 7. Wiley-VCH Verlag GmbH, 1997.
- Hofmann, Joerg,Schulz, Kathrin,Altmann, Annett,Findeisen, Matthias,Zimmermann, Gerhard
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p. 2541 - 2548
(2007/10/03)
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- A novel C-H insertion via deoxygenation of amides by a Sm/SmI2 mixed system
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A samarium/samarium diiodide mixed system successfully effects novel aminocyclopropanation and C-H insertion via the deoxygenation of amides. Styrenes undergo aminocyclopropanation by the reaction with aromatic amides, samarium metal, and samarium diiodide. Furthermore, the reaction of aliphatic amides with Sm/SmI2 in the presence of alkylbenzenes like toluene causes benzylic C-H insertion giving the corresponding phenylethylamine derivatives in good yields.
- Ogawa, Akiya,Takami, Noriaki,Nanke, Taizoh,Ohya, Syoji,Hirao, Toshikazu,Sonoda, Noboru
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p. 12895 - 12902
(2007/10/03)
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- KF-Al2O3 induced condensations of indene with aromatic aldehydes
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In the presence of KF-Al2O3 as a solid catalyst, indene reacted with aromatic aldehydes 2a-c (R=4-Me, 4-MeO, 4-Me2N) to yield mainly benzofulvenes 3a-c (45%-66%), while when treated with two molar of aromatic aldehydes 2d-
- Lu, Wenxing,Zhu, Quan,Yan, Chao-Guo
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p. 3985 - 3990
(2007/10/03)
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- Photochemistry of 1-Phenyl-1,2-dihydronaphthalene in Methanol
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The photochemistry of 1-phenyl-1,2-dihydronaphthalene (1) in methanol and hexane has been investigated.The lack of influence of solvent polarity and of the presence of sulfuric acid on the rate of formation of exo-4-phenylbenzobicyclohex-2-ene (exo-2) from the primary, ring-opened photoproduct cZt-3a of 1 precludes a sudden-polarized, zwitterionic excited state from being involved in the intramolecular photocycloaddition reaction leading to exo-2.The experimental results can be rationalized by assuming that this photoprocess involves a concerted ?4a+ ?2a-type electrocyclic reaction. cis-Dibenzobicycloocta-2,7-diene (8) is proposed to arise by photocyclization of cZc-3b, followed by a thermal rearrangement.On irradiation of 1 with a broad-spectrum lamp, the ratio of the photoproducts exo-2 and 8 is correlated with the ratio of the pe and pa conformers of 1.The novel compound 1-(o-benzylphenyl)allene (6) is also formed under these conditions.Irradiation of 1 at 254 nm yields 8 as the only photoproduct.Photochemical addition of methanol was observed to complete with the photoprocess, leading to exo-2, though at a comparatively low level.A photodecomposition mode of exo-2, presumably involving heterolytic cleavage of the cyclopropane ring, presents the chief source of methoxylated photoproducts at low temperatures in methanol.
- Woning, Jan,Lijten, Frank A. T.,Laarhoven, Wim H.
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p. 2427 - 2435
(2007/10/02)
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- METHYLENE-CARBONYL CONDENSATIONS OF SOME CH ACIDS WITH ALDEHYDES UNDER THE CONDITIONS OF PHASE-TRANSFER CATALYSIS OR CATALYSIS BY THE FLUORIDE ION
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The condensation of a series of CH acids (fluorene, phenylacetonitrile, ethene) with aromatic aldehydes was realized in the aqueous sodium hydroxide-organic solvent-phase-transfer catayst system. 9-Substituted fluorenes do not enter into condensation under the indicated conditions.The condensation of fluorene, PhCH2CN, CH2(CN)2, and CH2(CN)COOEt with benzaldehyde and also of CH2(CN)COOEt with cyclohexanone was realized in the presence of tetrabutylammonium fluoride , deposited on silika gel.It was shown that the yield of the produt from crotonic condensation in the reaction of CH2(COOEt)2 with benzaldehyde is small, and this is due to the instability of PhCH=C(COOEt)2 under the reaction conditions.Sodiomalonic ester was condensed with benzaldehyde in the presence of titanium tetrachloride or aluminum chloride.
- Beletskaya, I.P.,Gulyukina, N.S.,Ali Ali, Muhamed,Solov'yanov, A.A.,Reutov, O.A.
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p. 657 - 661
(2007/10/02)
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