- Radical polymerization of 2,5-norbornadienes containing ester groups by AIBN and oxygen gas
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New 2,5-norbornadiene-type monomers bearing 1-adamantyl and cyclohexyl ester groups on their 2-position polymerized with azobisisobutyronitrile to form the polymers consisting of two types of polymer unit structures. The major part had a saturated nortricyclene framework, which was formed by 2,6-addition along with intramolecular cyclization on the norbornadiene moiety. The minor part consisted of 2-norbornene-type units constructed via 2,3-addition. A series of norbornadiene-based monomers spontaneously polymerized in the presence of oxygen. Because a radical inhibitor, namely hydroquinone, could suppress this spontaneous reaction, it was indicated that the oxygen-induced polymerization proceeds via free-radical polymerization mechanism. Changing a quantity of provided oxygen gas (O2) to a norbornadiene monomer significantly affected on polymerization results, in specific, molecular weight of the formed polymer, which indicated that oxygen serves as one of the key reagents for the formation of free-radical initiating species. It was proven that the combination of norbornadiene ethyl ester with O2 was applicable as a new free-radical initiator for polymerization of methyl methacrylate.
- Shiotsuki, Masashi,Kai, Hironobu,Endo, Takeshi
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- Photoinduced intramolecular cyclopentanation vs photoprotolytic oxametathesis in polycyclic alkenes outfitted with conformationally constrained aroylmethyl chromophores
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Intramolecular photoinduced cyclizations are investigated in photoprecursors assembled in a modular fashion via a Diels-Alder reaction of acetylenic dienophiles with subsequent Michael additions of aromatic ketones to install a chromophore capable of initiating Paternò-Büchi cycloadditions or radical cyclization cascades. The protolytic oxametathesis in these systems allows for rapid access to novel polycyclic scaffolds decorated by formyl groups and carboxylates suitable for subsequent modifications. In conformationally constrained photoprecursors, a radical rearrangement takes place resulting in intramolecular 1,3-diradical cyclopentanation of the double bond.
- Valiulin, Roman A.,Arisco, Teresa M.,Kutateladze, Andrei G.
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p. 2012 - 2025
(2013/05/21)
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- Synchronous enantiomeric enrichment of both reactant and product by absolute asymmetric synthesis using circularly polarized light. Part 3. Numerical simulation and experimental verification of the reversible asymmetric photoisomerization between methyl norbornadiene-2-carboxylate and methyl quadricyclane-1-carboxylate
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In the first paper of this series, we proposed a new absolute asymmetric synthesis (NAAS) with circularly polarized light (CPL), which can be classified into two subcategories: (a) reversible NAAS (CPL excites both the reactant and product), (b) irreversible NAAS (the reactant only is excited by CPL). In the present paper we deal with reversible NAAS. The numerical simulations, which are based upon the results of the preceding paper of this series, are performed. Using the reversible photoisomerization between methyl norbornadiene-2-carboxylate (I) and methyl quadricyclane-1-carboxylate (II), it was experimentally verified that the enantiomeric excesses (ee's) of both the reactant and product were critically dependant not only on the anisotropy factors (g = Δε/ε) of both components, but also on the relative quantum yields of the forward and reverse reactions. In the case of reversible NAAS, the ee of the reactant and the product will concurrently increase according to the conversion, and attain appreciable values at the photostationary state if we appropriately select the system and the CPL-irradiation wavelength in such a way that if the g factors of the product and the reactant are large enough, the sign of the g factor of the product is opposite to that of the reactant, and the photochemical equilibrium constant K is less than unity.
- Nishino,Nakamura,Shitomi,Onuki,Inoue
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p. 1706 - 1713
(2007/10/03)
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- Synchronous enantiomeric enrichment of both reactant and product by absolute asymmetric synthesis using circularly polarized light. Part 1. Theoretical and experimental verification of the asymmetric photoisomerization of methyl norbornadiene-2-carboxylate to methyl quadricyclane-1-carboxylate
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We propose a new absolute asymmetric synthesis (NAAS), in which the irradiation with left- or right-handed circularly polarized light (CPL) of a racemic reactant leads to the synchronous enantiomeric enrichment of both reactant and product. NAAS has two subcategories: (a) reversible NAAS (CPL excites both the reactant and the product), (b) irreversible NAAS (only the reactant is excited by CPL). Here in the first paper of this series of papers we consider irreversible NAAS. We have deduced the theoretical equations that determine the relationship between the enantiomeric excesses (ee's) of both reactant and product and the progress of the CPL-induced photoreaction. Using the clear and reversible photoisomerization of chiral methyl norbornadiene-2-carboxylate (I) to chiral methyl quadricyclane-1-carboxylate (II) by CPL-irradiation in acetonitrile, we experimentally verified the equations. The ee's of both reactant and product are remarkably dependent on the anisotropy factor (g = Δε/ε) of the reactant. The ee of the reactant increases to 100% if the irradiation is continued to the stage that nearly all of the reactant is consumed. Conversely, the ee of the product gradually decreases from g/2 during the initial stages to zero at the final stage of the irradiation. This is the first time that the relationship between the ee of product and the progress of the photoreaction is experimentally examined based upon theoretical considerations.
- Nishino,Nakamura,Inoue
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p. 1693 - 1700
(2007/10/03)
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- Chiral bis(oxazoline)copper(II) complexes as lewis acid catalysts for the enantioselective Diels-Alder reaction
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Bis(oxazoline)copper(II) complexes are highly enantioselective catalysts in Diels-Alder reactions involving bidentate dienophiles. Cationic [Cu((S,S)- t-Bu-box)]X2 complexes with different counterions have been used as catalysts, revealing a profound influence of the counterion on the rate and stereoselectivity of the catalyst. A square-planar catalyst-substrate complex is proposed to account for the high diastereo- and enantioselectivities observed. Three bis(oxazoline)-Cu(II) X-ray structures have been obtained that support this model. Double-stereodifferentiating experiments, performed employing chiral dienophiles, afforded results that are fully consistent with the proposed square-planar transition-state assemblage. In addition to imide- based substrates, α,β-unsaturated thiazolidine-2-thiones have been introduced as a new class of dienophiles with enhanced reactivity. Kinetics experiments were performed to quantify the role that product inhibition plays in the course of the reaction. Rate and equilibrium binding constants of various catalyst inhibitors were also derived from the kinetic analysis. A comparative study was undertaken to elucidate the differences between the bis(oxazoline)-Cu(II) catalyst and the bis(oxazoline) catalysts derived from Fe(III), Mg(II), and Zn(II). Catalyst performance was found to be a function of a subtle relationship between bis(oxazoline) structure and transition metal.
- Evans, David A.,Miller, Scott J.,Lectka, Thomas,Von Matt, Peter
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p. 7559 - 7573
(2007/10/03)
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- Nickel-catalyzed [2π + 2π + 2π] (homo-Diels - Alder) and [2π + 2π] cycloadditions of bicyclo[2.2.1]hepta-2,5-dienes
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Active catalysts which promote the homo-Diels - Alder (HDA) cycloaddition with a variety of electron-deficient olefins with bicyclo[2.2.1]hepta-2,5-diene (norbornadiene, NBD) have been developed. The nickel complex and the additives (e.g., ligands, reduci
- Lautens, Mark,Edwards, Louise G.,Tam, William,Lough, Alan J.
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p. 10276 - 10291
(2007/10/03)
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- Regiochemical Control in the Homo-Diels-Alder Reaction: Substituent Effects
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The regio- and stereoselectivity of the cycloaddition between substituted norbornadienes and electron-deficient olefins catalyzed by nickel complexes has been studied.The diene and dienophile substituents as well as the ligand were found to exert a dramat
- Lautens, Mark,Edwards, Louise G.
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p. 3761 - 3763
(2007/10/02)
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- Cycloaddition Behavior of 2-Substituted Norbornadienes towards 4-Phenyl-1H-1,2,4-triazole-3,5-dione (PTAD): Homo Diels-Alder Reactivity versus Insertion, Rearrangement, and Cycloaddition
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The reaction of PTAD with 2-trimethylsilyl-, 2-chloro-, 2-cyano-, and 2-methoxycarbonylnorbornadienes 1 a-d, respectively, was investigated.In all cases homo Diels-Alder adducts were obtained, for 1a the unexpected regioisomer, the 1-trimethylsilyl derivative 2a, and for other norbonadienes 1 b-d the usual cyclopropane-substituted products 2 b-d.Except for the trimethylsilyl sytem 1a, for which also the dicarboximides 4a and 4'a, respectively, (rearrangement urazoles) were obtained, the other norbornadienes 1b-d afforded the insertion products 5 b-d.With increasing electron-withdrawal by the 2-substituents the insertion products 5 b-d increased at the expense of the homo Diels-Alder adducts 2 b-d.These results are mechanistically rationalized in terms of stepwise cycloaddition via 1,5-dipolar intermediates.In the case of 2-chloronorbornadiene (1b), besides the homo Diels-Alder 2b, the rearrangement urazole 4b and the insertion product 5b, also the cycloadduct 3b was formed.
- Adam, Waldemar,Lucchi, Ottorino de,Pasquato, Lucia,Will, Bernd
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p. 531 - 536
(2007/10/02)
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- SYNTHESIS OF 4-METHYLENE-1-CYCLOPENTENES
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4-Methylene-1-cyclopentenes are available via the cycloaddition of palladium-trimethylenemethane to substituted bicyclohepta-2,5-dienes followed by flash vacuum thermolysis.
- Trost, Barry M.,Balkovec, James M.,Angle, Steven R.
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p. 1445 - 1448
(2007/10/02)
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- COBALT(II)TETRAPORPHYRIN-CATALYZED ISOMERISATION OF ELECTRONEGATIVE SUBSTITUTED QADRICYCLANES
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Co(II)TPP-catalyzed isomerisation of a series of electronegative substituted quadricyclanes(1) to the corresponding norbornadiene(2) was found to proceed via radicophilic attack of the metal to 1.
- Miki, Sadao,Ohno, Toshinobu,Iwasaki, Hideaki,Yoshida, Zen-ichi
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p. 3487 - 3490
(2007/10/02)
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- Nucleophilic Exchange Reactions at 1-Chloroquadricyclane: 1,5- and 1,7-Dehydroquadricyclane as Reactive Intermediates.
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Quadricyclane was metalated at position 1 to 1b in high yield by the complex of butyllithium and tetramethylethylenediamine or by a mixture of butyllithium and potassium tert-butoxide.Numerous 1-substituted quadricyclanes were accessible via 1b.Nuclophilic substitution products were obtained by the reaction of 1-chloroquadricyclane with organolithium compounds, lithium amides, and with lithium ethylthiolate (in the presence of a bulky strong base), which could be isomerized to the corresponding norbornadienes.Mechanistic investigations have shown that 1,7- and 1,5-dehydroquadricyclane (4 and 5) were involved as reactive intermediates.The nucleophilic substitution of optical active 1-chloroquadricyclane with lithium dimethylamide proceeded with 96percent racemization.This result is in accord with an elimination-addition mechanism passing over 4 and 5.
- Baumgaertel, Otto,Szeimies, Guenter
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p. 2180 - 2204
(2007/10/02)
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