The Experts below are selected from a list of 249 Experts worldwide ranked by ideXlab platform
Osamu Haba - One of the best experts on this subject based on the ideXlab platform.
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Ring-opening polymerization of a five-membered lactone trans-fused to a Cyclohexane Ring
Polymer Journal, 2014Co-Authors: Osamu Haba, Hiroki ItabashiAbstract:The Ring-opening polymerization behavior of five-membered lactones fused to a Cyclohexane Ring, T6L and C6L, was investigated under various conditions. The t-BuOK-initiated anionic polymerization of T6L produces polymers having M n values of 5000. In remarkable contrast, C6L did not polymerize at all, implying the increase in Ring strain of the lactone Ring by trans -fused Cyclohexane. The anionic polymerization of T6L was reversible, and the thermodynamic parameters characterizing the polymerization of T6L were estimated to be Δ H _p°=−18 kJ·mol^−1 and Δ S _p°=–65 J·K^−1mol^−1. The Ring-opening polymerization behavior of five-membered lactones fused to a Cyclohexane Ring (that is, the trans - and cis -hexahydro-2(3 H )-benzofuranone denoted T6L and C6L, respectively) was investigated under various conditions. The potassium tert -butoxide (^tBuOK)-initiated anionic polymerization of T6L yields polymers with number-average molecular weight ( M n) values of 5000. However, no polymeric products were obtained via cationic and coordination polymerization. Among the anionic initiators, a base stronger than an alkoxide initiated the polymerization of T6L. In contrast, cis -isomer C6L did not polymerize regardless of the initiator species used, which implied an increase in the Ring strain of the lactone Ring by the trans -fused Cyclohexane. The anionic polymerization of T6L was reversible, and the thermodynamic parameters characterizing the polymerization of T6L were estimated to be Δ H _p°=−18 kJ·mol^−1 and Δ S _p°=–65 J·K^−1mol^−1 on the basis of the measurement of the equilibrium monomer concentration.
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The anionic Ring-opening polymerization of five-membered cyclic carbonates fused to the Cyclohexane Ring
Polymer Journal, 2013Co-Authors: Kunio Tezuka, Kazuhito Komatsu, Osamu HabaAbstract:The anionic polymerization of five-membered cyclic carbonates fused to a Cyclohexane Ring, that is, the trans - and cis -Cyclohexane-1,2-diyl carbonates ( trans - and cis - 1 , respectively), were examined as a model polymerization example to reveal the origin of the unusually good polymerizability of the previously reported methyl 4,6- O -benzylidene-2,3- O -carbonyl- α ,D-glucopyranoside. The tert -BuOK-initiated anionic polymerization of trans - 1 produces polymers with M _n values of 11 000, whereas no polymeric products were obtained from cis - 1 . The structure of the poly( trans - 1 ) was confirmed by comparison with the model carbonate (2) based on the ^13C NMR spectra as well as the hydrolysis experiments. The poly( trans - 1 ) form essentially consists of polycarbonate units; therefore, the polymerization of trans - 1 was not accompanied by any decarboxylation. The thermodynamic parameters for the polymerization of trans - 1 were estimated to be Δ H _p°=−23 kJ mol^−1 and Δ S _p°=−63 J K^−1 mol^−1. The anionic Ring-opening polymerizations of trans- and cis -1 were carried out using tert -BuOK as the initiator. The bulk polymerization of trans -1 proceeded without the elimination of CO_2, but cis -1 gave no polymeric product. The thermal analysis indicates that trans -1 has extraordinarily large Ring strain for five-membered cyclic carbonates, and is close to six-membered cyclic carbonates that have good Ringopening polymerizability.
Goran Petrovic - One of the best experts on this subject based on the ideXlab platform.
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[4+2] Cyclohexane Ring Formation by a Tandem of a Free Radical Alkylation of a Non-Activated δ-Carbon Atom and Intramolecular Carbanion Cycloalkylation
Synthesis, 2004Co-Authors: Goran Petrovic, Živorad ČekovićAbstract:A[4+2] Cyclohexane Ring formation was achieved by the combination of free radical and ionic reaction sequences. Free radical alkylation of the remote non-activated δ-carbon atom involves addition of 8-carbon radicals, generated by 1,5-hydrogen transfer in alkoxyl radical intermediates, to the radicophilic olefins, while the polar sequence involves the enolate anions as intermediates which undergo a cycloalkylation reaction. The Cyclohexane Rings were constructed using diverse acyclic compounds 15 and 18 as well as cyclic alkyl arenesulfenates (e.g., 5, 24, 27) as the precursors of alkoxyl radicals (four-carbon atom fragment) and methyl vinyl ketone or other activated olefins as two-carbon atom fragments. Annulation of the Cyclohexane Ring was applied for the synthesis of a variety of cyclic systems including monocyclic (17 and 20), fused-Rings (e.g. 23, 26, 29) and spirocyclic systems (7).
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Synthesis of tetrahydrokhusitone: Annulation of the Cyclohexane Ring by free radical and carbanionic sequence of reactions
Journal of the Serbian Chemical Society, 2003Co-Authors: Goran Petrovic, Z. CekovicAbstract:The synthesis of norcadinane sesquiterpene tetrahydrokhusitone 1 has been achieved by a new method for annulation of Cyclohexane Ring involving a sequence of free radical -alkylation of the non-activated carbon atom and intramolecular carbanionic alkylation. (-)-Menthol was used as the starting compound.
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Annulation of the Cyclohexane Ring by Tandem Free Radical Alkylation of a Nonactivated δ-Carbon Atom−Intramolecular Carbanion Cycloalkylation
Organic letters, 2000Co-Authors: Goran Petrovic, Zivorad CekovicAbstract:Annulation of the Cyclohexane Ring by a combination of free radical and ionic reactions sequences was achieved. Free radical alkylation of the remote nonactivated δ-carbon atom involves addition of δ-carbon radicals, generated by 1,5-hydrogen transfer in alkoxy radical intermediates, to radicophilic olefins, while the polar sequence involves enolate anions as intermediates which undergo a cycloalkylation reaction. Thus, the Cyclohexane Ring was constructed using diverse acyclic and cyclic structures as precursors of alkoxy radicals.
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annulation of the Cyclohexane Ring by tandem free radical alkylation of a nonactivated δ carbon atom intramolecular carbanion cycloalkylation
Organic Letters, 2000Co-Authors: Goran Petrovic, Zivorad CekovicAbstract:Annulation of the Cyclohexane Ring by a combination of free radical and ionic reactions sequences was achieved. Free radical alkylation of the remote nonactivated δ-carbon atom involves addition of δ-carbon radicals, generated by 1,5-hydrogen transfer in alkoxy radical intermediates, to radicophilic olefins, while the polar sequence involves enolate anions as intermediates which undergo a cycloalkylation reaction. Thus, the Cyclohexane Ring was constructed using diverse acyclic and cyclic structures as precursors of alkoxy radicals.
Ángel Carretero - One of the best experts on this subject based on the ideXlab platform.
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Diastereopure Synthesis of Novel Cyclohexane-Ring-Based Constrained Lanthionine and α-Methyllanthionine through an SN2 Reaction with a β-Bromoalanine as a Key Step
Synlett, 2020Co-Authors: Iñaki Osante, Carlos Cativiela, Jaime Gracia-vitoria, Ángel CarreteroAbstract:Here we report the diastereopure synthesis of a novel protected lanthionine derivative substituted with a Cyclohexane Ring as well as the diastereopure synthesis of an α-methyllanthionine derivative. By starting from enantiopure α,β-Cyclohexane-substituted cystine, or α-methylcysteine, we designed a straightforward route that permits the preparation of orthogonally protected modified lanthionines in diastereopure form. The key step of the methodology is the formation of a thioether bond through the use of an β-bromoalanine derivative. The strategy developed should be valuable in the preparation of a wide range of modified constrained lanthionines that might be finally attached to a peptide sequence, which would be especially useful in the syntheses of novel lantibiotics.
Kunio Tezuka - One of the best experts on this subject based on the ideXlab platform.
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The anionic Ring-opening polymerization of five-membered cyclic carbonates fused to the Cyclohexane Ring
Polymer Journal, 2013Co-Authors: Kunio Tezuka, Kazuhito Komatsu, Osamu HabaAbstract:The anionic polymerization of five-membered cyclic carbonates fused to a Cyclohexane Ring, that is, the trans - and cis -Cyclohexane-1,2-diyl carbonates ( trans - and cis - 1 , respectively), were examined as a model polymerization example to reveal the origin of the unusually good polymerizability of the previously reported methyl 4,6- O -benzylidene-2,3- O -carbonyl- α ,D-glucopyranoside. The tert -BuOK-initiated anionic polymerization of trans - 1 produces polymers with M _n values of 11 000, whereas no polymeric products were obtained from cis - 1 . The structure of the poly( trans - 1 ) was confirmed by comparison with the model carbonate (2) based on the ^13C NMR spectra as well as the hydrolysis experiments. The poly( trans - 1 ) form essentially consists of polycarbonate units; therefore, the polymerization of trans - 1 was not accompanied by any decarboxylation. The thermodynamic parameters for the polymerization of trans - 1 were estimated to be Δ H _p°=−23 kJ mol^−1 and Δ S _p°=−63 J K^−1 mol^−1. The anionic Ring-opening polymerizations of trans- and cis -1 were carried out using tert -BuOK as the initiator. The bulk polymerization of trans -1 proceeded without the elimination of CO_2, but cis -1 gave no polymeric product. The thermal analysis indicates that trans -1 has extraordinarily large Ring strain for five-membered cyclic carbonates, and is close to six-membered cyclic carbonates that have good Ringopening polymerizability.
Zivorad Cekovic - One of the best experts on this subject based on the ideXlab platform.
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Annulation of the Cyclohexane Ring by Tandem Free Radical Alkylation of a Nonactivated δ-Carbon Atom−Intramolecular Carbanion Cycloalkylation
Organic letters, 2000Co-Authors: Goran Petrovic, Zivorad CekovicAbstract:Annulation of the Cyclohexane Ring by a combination of free radical and ionic reactions sequences was achieved. Free radical alkylation of the remote nonactivated δ-carbon atom involves addition of δ-carbon radicals, generated by 1,5-hydrogen transfer in alkoxy radical intermediates, to radicophilic olefins, while the polar sequence involves enolate anions as intermediates which undergo a cycloalkylation reaction. Thus, the Cyclohexane Ring was constructed using diverse acyclic and cyclic structures as precursors of alkoxy radicals.
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annulation of the Cyclohexane Ring by tandem free radical alkylation of a nonactivated δ carbon atom intramolecular carbanion cycloalkylation
Organic Letters, 2000Co-Authors: Goran Petrovic, Zivorad CekovicAbstract:Annulation of the Cyclohexane Ring by a combination of free radical and ionic reactions sequences was achieved. Free radical alkylation of the remote nonactivated δ-carbon atom involves addition of δ-carbon radicals, generated by 1,5-hydrogen transfer in alkoxy radical intermediates, to radicophilic olefins, while the polar sequence involves enolate anions as intermediates which undergo a cycloalkylation reaction. Thus, the Cyclohexane Ring was constructed using diverse acyclic and cyclic structures as precursors of alkoxy radicals.
