The Experts below are selected from a list of 99 Experts worldwide ranked by ideXlab platform
Yasuji Yamada - One of the best experts on this subject based on the ideXlab platform.
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Total synthesis of the dolabellane marine diterpenoids, claenone, palominol and dolabellatrienone
Tetrahedron, 2003Co-Authors: Hiroaki Miyaoka, Yutaka Isaji, Hidemichi Mitome, Yasuji YamadaAbstract:Abstract The synthesis of marine dolabellane diterpenoids claenone, palominol and dolabellatrienone was conducted from d -mannitol. In each case, formation of the bicyclo[2.2.1]Heptane Derivative by sequential Michael reaction, preparation of the tetrasubstituted cyclopentane Derivative by retro-aldol reaction and cyclization of sulfone were involved as key steps.
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Total synthesis of marine diterpenoid stolonidiol
Tetrahedron Letters, 2001Co-Authors: Hiroaki Miyaoka, Hidemichi Mitome, Tomohiro Baba, Yasuji YamadaAbstract:Abstract Marine dolabellane diterpenoid stolonidiol was synthesized from l -ascorbic acid. The method for this total synthesis involves formation of the bicyclo[2.2.1]Heptane Derivative using a diastereoselective sequential Michael reaction, formation of cyclopentane Derivative by the retro-aldol reaction and construction of an 11-membered carbocyclic ring through the intramolecular Horner–Wadsworth–Emmons reaction.
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Total synthesis of dolabellane diterpenoid claenone
Tetrahedron Letters, 1998Co-Authors: Hiroaki Miyaoka, Yutaka Isaji, Yasuhiro Kajiwara, Iyo Kunimune, Yasuji YamadaAbstract:Abstract Marine dolabellane diterpenoid claenone ( 1 ) was synthesized from D-mannitol. This synthesis involves the formation of bicyclo[2.2.1]Heptane Derivative 4a by sequential Michael reaction, the formation of cyclopentane Derivative 9 by retro-aldol reaction and the cyclization of sulfone 19 .
Katsuyoshi Yamasaki - One of the best experts on this subject based on the ideXlab platform.
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impact of diradical spin state singlet vs triplet and structure puckered vs planar on the photodenitrogenation stereoselectivity of 2 3 diazabicyclo 2 2 1 Heptanes
Journal of Physical Chemistry B, 2016Co-Authors: Saori Tada, Takemi Mizuno, Katsuyoshi YamasakiAbstract:Versatile transformations of azo compounds are utilized not only in synthetic organic chemistry but also in materials science. In this study, a hitherto unknown stereoselectivity was observed by low-temperature in situ NMR spectroscopy for the photochemical denitrogenation of a cyclic azoalkane (2,3-diazabicyclo[2.2.1]Heptane) Derivative. Direct (singlet) photodenitrogenation at 188 K afforded two products, the configurationally retained ring-closed compound (ret-CP) and the inverted compound (inv-CP), in a ratio of 82/18 (±3) (ret-CP/inv-CP), with an overall yield of >95%. Triplet-sensitized denitrogenation at 199 K using benzophenone (3BP*) or xanthone (3Xan*) selectively produced inv-CP, with a ret-CP/inv-CP ratio of 7/93 (±3). Thermal isomerization of inv-CP into ret-CP was observed by low-temperature NMR spectroscopy. Transient absorption spectroscopy revealed that two distinct singlet diradicals are involved in the formation of CP during direct photodenitrogenation, that is, puckered puc-1DR and pla...
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Impact of Diradical Spin State (Singlet vs Triplet) and Structure (Puckered vs Planar) on the Photodenitrogenation Stereoselectivity of 2,3-Diazabicyclo[2.2.1]Heptanes
2016Co-Authors: Manabu Abe, Saori Tada, Takemi Mizuno, Katsuyoshi YamasakiAbstract:Versatile transformations of azo compounds are utilized not only in synthetic organic chemistry but also in materials science. In this study, a hitherto unknown stereoselectivity was observed by low-temperature in situ NMR spectroscopy for the photochemical denitrogenation of a cyclic azoalkane (2,3-diazabicyclo[2.2.1]Heptane) Derivative. Direct (singlet) photodenitrogenation at 188 K afforded two products, the configurationally retained ring-closed compound (ret-CP) and the inverted compound (inv-CP), in a ratio of 82/18 (±3) (ret-CP/inv-CP), with an overall yield of >95%. Triplet-sensitized denitrogenation at 199 K using benzophenone (3BP*) or xanthone (3Xan*) selectively produced inv-CP, with a ret-CP/inv-CP ratio of 7/93 (±3). Thermal isomerization of inv-CP into ret-CP was observed by low-temperature NMR spectroscopy. Transient absorption spectroscopy revealed that two distinct singlet diradicals are involved in the formation of CP during direct photodenitrogenation, that is, puckered puc-1DR and planar pl-1DR diradicals. The former produces ret-CP, whereas the latter affords inv-CP. Kinetic analysis using the integrated profiles method was used to determine the molecular absorption coefficient of pl-1DR (ε560 = 4900 ± 250 M–1 cm–1) for the first time. The involvement of the puckered singlet diradical resolves the mechanistic puzzle of stereoselective denitrogenation of diazabicycloHeptane-type azoalkanes
Hiroaki Miyaoka - One of the best experts on this subject based on the ideXlab platform.
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Total synthesis of the dolabellane marine diterpenoids, claenone, palominol and dolabellatrienone
Tetrahedron, 2003Co-Authors: Hiroaki Miyaoka, Yutaka Isaji, Hidemichi Mitome, Yasuji YamadaAbstract:Abstract The synthesis of marine dolabellane diterpenoids claenone, palominol and dolabellatrienone was conducted from d -mannitol. In each case, formation of the bicyclo[2.2.1]Heptane Derivative by sequential Michael reaction, preparation of the tetrasubstituted cyclopentane Derivative by retro-aldol reaction and cyclization of sulfone were involved as key steps.
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Total synthesis of marine diterpenoid stolonidiol
Tetrahedron Letters, 2001Co-Authors: Hiroaki Miyaoka, Hidemichi Mitome, Tomohiro Baba, Yasuji YamadaAbstract:Abstract Marine dolabellane diterpenoid stolonidiol was synthesized from l -ascorbic acid. The method for this total synthesis involves formation of the bicyclo[2.2.1]Heptane Derivative using a diastereoselective sequential Michael reaction, formation of cyclopentane Derivative by the retro-aldol reaction and construction of an 11-membered carbocyclic ring through the intramolecular Horner–Wadsworth–Emmons reaction.
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Total synthesis of dolabellane diterpenoid claenone
Tetrahedron Letters, 1998Co-Authors: Hiroaki Miyaoka, Yutaka Isaji, Yasuhiro Kajiwara, Iyo Kunimune, Yasuji YamadaAbstract:Abstract Marine dolabellane diterpenoid claenone ( 1 ) was synthesized from D-mannitol. This synthesis involves the formation of bicyclo[2.2.1]Heptane Derivative 4a by sequential Michael reaction, the formation of cyclopentane Derivative 9 by retro-aldol reaction and the cyclization of sulfone 19 .
Jacques Eustache - One of the best experts on this subject based on the ideXlab platform.
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A simple spiroepoxide as methionine aminopeptidase-2 inhibitor: synthetic problems and solutions
Tetrahedron Letters, 2005Co-Authors: Vincent Rodeschini, Pierre Van De Weghe, Céline Tarnus, Jacques EustacheAbstract:Abstract The preparation of a simple 1-oxa-spiro[2.4]Heptane Derivative is described. Observations made in the course of the synthesis show again that apparently minor structural modifications of the dienic substrate exert a strong influence on the ring-closing metathesis outcome and that the efficient construction of even simple but highly substituted systems by RCM may constitute a synthetic challenge.
Wojciech Sas - One of the best experts on this subject based on the ideXlab platform.
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synthesis structure of 7 oxa 1 azabicyclo 2 2 1 Heptane Derivative obtained from sugar nitrone and analysis of its conformational variety
Journal of Molecular Structure, 2019Co-Authors: Tomasz Rowicki, Izabela D Madura, Paulina H Marek, Karolina Kopczynska, Ewa Mironiukpuchalska, Wojciech SasAbstract:Abstract Dispiro Derivative of 7-oxa-1-azabicyclo [2.2.1]Heptane 5 was synthesized as a single stereoisomer from N-(5-allyl-spiro [1,3-dioxan-2,1′-cyclohexane]-5-yl)hydroxylamine 2 and protected d -mannose 3, through intramolecular 1,3-dipolar cycloaddition of in situ formed N-(but-3-en-1-yl)nitrone 4. Structure of product 5 was attributed on the basis of NMR and X-ray analyses. In the solid state, three crystallographically independent molecules of 5 were detected, every exhibiting a different orientation of spiro connected rings. Conformational analysis performed by DFT calculations in the gas phase was performed and revealed that the conformations observed in the crystal correspond to the most stable molecular geometries. Two of them were also found to be dominant in solution.
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Asymmetric synthesis of novel polyhydroxylated Derivatives of indolizidine and quinolizidine by intramolecular 1,3-dipolar cycloaddition of N-(3-alkenyl)nitrones
Chemical Communications, 2001Co-Authors: Piotr Gebarowski, Wojciech SasAbstract:Reaction of 3-O-benzyl-1,2-O-isopropylidene-1,5-pentadialdo-α- D-xylofuranose with N-(1,1-dimethylbut-3-enyl)hydroxylamine followed by intramolecular 1,3-dipolar cycloaddition yields 7-oxa-1-azabicyclo[2.2.1]Heptane Derivative 4, which is easily converted into novel polyhydroxylated quinolizidine 6 and indolizidine 8.