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Hans‐ulrich Reißig - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of Enantioenriched 2‐Substituted 4‐Phenylbutylamines by Hydrogenolysis of Optically Pure 6‐Alkoxy‐5,6‐dihydro‐4H‐1,2‐oxazines
European Journal of Organic Chemistry, 2002Co-Authors: Monika Buchholz, Florian Hiller, Hans‐ulrich ReißigAbstract:Lewis acid promoted exchange of the 6-ethoxy group of 6H-1,2-oxazines 1−3 with (−)-menthol furnished the optically active heterocycles 4−6. Diastereomers 4a and 4b, which could be separated efficiently by chromatography, were excellent substrates for highly diastereoselective conjugate additions of phenyllithium and n-butyllithium, thus providing the enantiopure trans-substituted 1,2-oxazines 7a, 7b, 8a, and 8b in good yields. Exhaustive hydrogenolysis of 7a afforded the primary amine 9 with an enantiomeric excess of 80%, whereas hydrogenolysis of 8a and 8b gave the corresponding amines (R)-11 and (S)-11, respectively, with an ee of more than 90%. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)
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Preparation of cyclic and bicyclic β-amino acids derivatives from methyl 6-ethoxy-5,6-dihydro-4H-1,2-oxazine-4-carboxylate
Synlett, 2002Co-Authors: Alexander A. Tishkov, Hans‐ulrich Reißig, Sema L. IoffeAbstract:The readily available methyl 6-ethoxy-5,6-dihydro-4H-1,2-oxazine-4-carboxylate (1) was alkylated at C-4 and acylated at the nitrogen atom. 1,2-Oxazine 1 and the resulting new substituted 1,2-oxazines 2 and 3 were suitableprecursors for the preparation of derivatives of β-proline, nipecotic acid, as well as indolizine-6- and quinolizine-3-carboxylic acids.
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Reactions of 6‐[bis(trimethylsilyl)amino]‐5,6‐dihydro‐4H‐1,2‐oxazines
Liebigs Annalen, 1995Co-Authors: Klaus Paulini, Andreas Gerold, Hans‐ulrich ReißigAbstract:1,2-Oxazine 1 was converted into an unusual condensation product 5 by treatment with tetra-n-butylammonium fluoride. The hydrogenolysis of 1 with Pd/C as catalyst provided the expected primary amine 9, whereas the same reaction with the ethoxycarbonyl-substituted 1,2-oxazine 2 as starting material gave the 4-methylproline derivative 10 after N-protection. Deprotonation at C-4 of 1 required rather harsh conditions but cleanly afforded the corresponding lithiated intermediate 11. Treatment of 11 with electrophiles provided the C-4-substituted derivatives 12–16 in good to moderate yield, but generally with very high diastereoselectivity. The overall substitution process preferentially occurs with retention of configuration which is explained by assuming ion pair structure B for intermediate 11.
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Reductive Transformations of 6H‐1,2‐Oxazines with Hydride Reagents: Formation of Aziridines and 3‐Hydroxyalkylated 1,2‐oxazines
European Journal of Organic Chemistry, 1993Co-Authors: Reinhold Zimmer, Kai Homann, Hans‐ulrich ReißigAbstract:6H-1,2-Oxazines 1 and 3 are converted into aziridines 2 and 4, respectively, by reduction with LiAlH4. Reduction of 1,2-oxazine 5 lacking the 6-alkoxy substituent leads to phenyl ketone 6, 6-Alkoxy-substituted 1,2-oxazine-3-carboxylates 7, 9, and 11 are reduced with NaBH4 to give the corresponding 3-hydroxymethylated compounds 8, 10, and 12 in good yields.
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Model studies of the reduction of 3‐phenyl‐6H‐1,2‐oxazines, chemo‐ and stereoselectivity: synthesis of amino alcohols, amino acids, and related compounds
Chemische Berichte, 1992Co-Authors: Reinhold Zimmer, Matthias Hoffmann, Hans‐ulrich ReißigAbstract:While palladium-catalyzed hydrogenation of 3-phenyl-6H-1,2-oxazine 1 produces primary amine 5 in a nitrogen-transposition reaction, the reductions of the related 1,2-oxazines 2, 10, and the 1,2-oxazin-6-one 3 afford the expected amino alcohols 4, 11, and the γ-amino acid 6, respectively, with low diastereoselectivites. In the presence of acetic acid 3 is reductively converted into γ-keto carboxylic acid 9 and 1 into the γ-lactam derivative 12 probably by a ring contraction to a nitrone intermediate. Raney nickel as the catalyst is able to transform 1,2-oxazine 7 bearing an exo-methylene unit into 3,4-dihydro-2H-pyrrole 13. The reaction of 6H-1,2-oxazine 1 with aluminium amalgam produces pyrrole 14 in moderate yield. Treatment of 1 with sodium in 2-propanol brings about its transformation into pyrrolidine derivative 15 together with pyrrole 14 and amino alcohol 4 as minor products. The chemoselectivity and stereoselectivity of these reductions are discussed including mechanistic proposals for the multistep processes involved.
Wolfgang Zinth - One of the best experts on this subject based on the ideXlab platform.
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NONEXPONENTIALITIES IN THE ULTRAFAST ELECTRON-TRANSFER DYNAMICS IN THE SYSTEM OXAZINE 1 IN N, N-DIMETHYLANILINE
Journal of Physical Chemistry A, 1999Co-Authors: S. Engleitner, M. Seel, Wolfgang ZinthAbstract:Transient absorption experiments with probing in the blue part of the spectrum (440−500 nm) are performed for the electron-transfer system oxazine 1 in N,N-dimethylaniline. The experiments with high time resolution of better than 20 fs show pronounced modulations due to high-frequency wave packet motion (600 cm -1) in the excited electronic state of the oxazine 1 molecule before electron transfer. Additionally, modulations due to wave packet motion in the product state of oxazine 1 after complete charge separation are observed. The absorption transients related to the electron transfer from N,N-dimethylaniline to oxazine 1 are clearly nonmonoexponential with time constants of 30 and 80 fs. This behavior points to a strong adiabaticity of the electron-transfer reaction with a high relevance of nuclear motions.
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Modulation of Ultrafast Electron Transfer Dynamics by Wavepacket Motion in Oxazine 1
Springer Series in Chemical Physics, 1998Co-Authors: S. Engleitner, M. Seel, B. Wolfseder, Gerhard Stock, Wolfgang Domcke, Wolfgang ZinthAbstract:Experiments with highest temporal resolution on the electron transfer in oxazine 1 show pronounced nonexponential reaction dynamics and wavepacket motion in the reaction product.
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Wavepacket motion and ultrafast electron transfer in the system oxazine 1 in N,N-dimethylaniline
Chemical Physics Letters, 1997Co-Authors: M. Seel, S. Engleitner, Wolfgang ZinthAbstract:Abstract Femtosecond experiments on the oxazine 1 in N,N-dimethylaniline electron transfer system have been performed with a cross-correlation width of less than 18 fs. The experiments exhibit two different ultrafast absorption changes: a fast decay of the transmission occurs on the 30–80 fs timescale. This feature is assigned to an extremely fast electron transfer. Superimposed on these kinetics, assigned to the electron transfer, are strong oscillations arising from the wavepacket motion on the ground and excited state electronic surfaces with frequencies of up to 18 THz.
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Wavepacket Motion Observed in an Ultrafast Electron Transfer System
Springer Series in Chemical Physics, 1996Co-Authors: Wolfgang Zinth, S. Engleitner, M. SeelAbstract:For a number of systems it has been shown that ultrafast electron transfer (ET) reactions can occur even faster than relevant medium reorganization and relaxation processes [1–3]. In this context, the role of specific reaction pathways and intramolecular vibrational modes becomes increasingly important. Here we want to present new experimental results for the well-known ET system oxazine 1 (OX) in N,N-dimethylaniline (DMA) recorded with highest time resolution. The data are compared to the reference system OX in 1-chloronaphtalene (1CN) having similar solvent properties (dipolemoment, dielectric constant, viscosity), however showing no ET.
M. Seel - One of the best experts on this subject based on the ideXlab platform.
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NONEXPONENTIALITIES IN THE ULTRAFAST ELECTRON-TRANSFER DYNAMICS IN THE SYSTEM OXAZINE 1 IN N, N-DIMETHYLANILINE
Journal of Physical Chemistry A, 1999Co-Authors: S. Engleitner, M. Seel, Wolfgang ZinthAbstract:Transient absorption experiments with probing in the blue part of the spectrum (440−500 nm) are performed for the electron-transfer system oxazine 1 in N,N-dimethylaniline. The experiments with high time resolution of better than 20 fs show pronounced modulations due to high-frequency wave packet motion (600 cm -1) in the excited electronic state of the oxazine 1 molecule before electron transfer. Additionally, modulations due to wave packet motion in the product state of oxazine 1 after complete charge separation are observed. The absorption transients related to the electron transfer from N,N-dimethylaniline to oxazine 1 are clearly nonmonoexponential with time constants of 30 and 80 fs. This behavior points to a strong adiabaticity of the electron-transfer reaction with a high relevance of nuclear motions.
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Modulation of Ultrafast Electron Transfer Dynamics by Wavepacket Motion in Oxazine 1
Springer Series in Chemical Physics, 1998Co-Authors: S. Engleitner, M. Seel, B. Wolfseder, Gerhard Stock, Wolfgang Domcke, Wolfgang ZinthAbstract:Experiments with highest temporal resolution on the electron transfer in oxazine 1 show pronounced nonexponential reaction dynamics and wavepacket motion in the reaction product.
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Wavepacket motion and ultrafast electron transfer in the system oxazine 1 in N,N-dimethylaniline
Chemical Physics Letters, 1997Co-Authors: M. Seel, S. Engleitner, Wolfgang ZinthAbstract:Abstract Femtosecond experiments on the oxazine 1 in N,N-dimethylaniline electron transfer system have been performed with a cross-correlation width of less than 18 fs. The experiments exhibit two different ultrafast absorption changes: a fast decay of the transmission occurs on the 30–80 fs timescale. This feature is assigned to an extremely fast electron transfer. Superimposed on these kinetics, assigned to the electron transfer, are strong oscillations arising from the wavepacket motion on the ground and excited state electronic surfaces with frequencies of up to 18 THz.
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Wavepacket Motion Observed in an Ultrafast Electron Transfer System
Springer Series in Chemical Physics, 1996Co-Authors: Wolfgang Zinth, S. Engleitner, M. SeelAbstract:For a number of systems it has been shown that ultrafast electron transfer (ET) reactions can occur even faster than relevant medium reorganization and relaxation processes [1–3]. In this context, the role of specific reaction pathways and intramolecular vibrational modes becomes increasingly important. Here we want to present new experimental results for the well-known ET system oxazine 1 (OX) in N,N-dimethylaniline (DMA) recorded with highest time resolution. The data are compared to the reference system OX in 1-chloronaphtalene (1CN) having similar solvent properties (dipolemoment, dielectric constant, viscosity), however showing no ET.
Sema L. Ioffe - One of the best experts on this subject based on the ideXlab platform.
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Rearrangement of 3-alkylidene-2-siloxy-tetrahydro-1,2-oxazines (ASENA). A new approach toward the synthesis of 3-α-hydroxyalkyl-5,6-dihydro-4H-1,2-oxazines
Tetrahedron, 2009Co-Authors: Andrey A. Tabolin, Alexey V. Lesiv, Yulia A. Khomutova, Yulia V. Nelyubina, Sema L. IoffeAbstract:Abstract A new approach toward the synthesis of 3-α-hydroxyalkyl-5,6-dihydro-4H-1,2-oxazines 1 from available 5,6-dihydro-4H-1,2-oxazine N-oxides 2 has been described. The key step of the process—the rearrangement of 3-alkiliden-2-siloxy-tetrahydro-1,2-oxazines 3 (ASENA)—was thoroughly investigated. Optimal experimental conditions were developed. A possible pathway of the ASENA rearrangement was proposed.
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2-Silyloxy-1,2-oxazines, a New Type of Acetals of Conjugated Nitroso Alkenes
Journal of Organic Chemistry, 2003Co-Authors: Alexander A. Tishkov, Alexey V. Lesiv, Yulya A. Khomutova, Yury A. Strelenko, Ivan D. Nesterov, Michael Yu. Antipin, Sema L. Ioffe, Scott E. DenmarkAbstract:3-Alkyl-substituted 1,2-oxazine N-oxides 2 can be selectively transformed into 2-silyloxy-1,2-oxazines 1 upon treatment with silylating reagents. In the solid state derivatives 1 adopt a chair conformation with the pyramidal nitrogen atom, whereas in solution they exist as an equilibrating mixture of two conformers (ΔG⧧ 55−60 kJ/mol). A preliminary study of the reactivity of nitrosals 1 has shown that they react with O- and N-stabilized carbocations to yield 1,2-oxazine N-oxides with a functionalized alkyl substituent at the 3-position. Moreover, compounds 1 can rearrange into silyloxy-1,2-oxazines 5 and react with morpholine to produce 3-morpholinoalkyl-1,2-oxazines 7 existing in a tautameric equilibrium with open-chain oximes 6.
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Preparation of cyclic and bicyclic β-amino acids derivatives from methyl 6-ethoxy-5,6-dihydro-4H-1,2-oxazine-4-carboxylate
Synlett, 2002Co-Authors: Alexander A. Tishkov, Hans‐ulrich Reißig, Sema L. IoffeAbstract:The readily available methyl 6-ethoxy-5,6-dihydro-4H-1,2-oxazine-4-carboxylate (1) was alkylated at C-4 and acylated at the nitrogen atom. 1,2-Oxazine 1 and the resulting new substituted 1,2-oxazines 2 and 3 were suitableprecursors for the preparation of derivatives of β-proline, nipecotic acid, as well as indolizine-6- and quinolizine-3-carboxylic acids.
S. Engleitner - One of the best experts on this subject based on the ideXlab platform.
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NONEXPONENTIALITIES IN THE ULTRAFAST ELECTRON-TRANSFER DYNAMICS IN THE SYSTEM OXAZINE 1 IN N, N-DIMETHYLANILINE
Journal of Physical Chemistry A, 1999Co-Authors: S. Engleitner, M. Seel, Wolfgang ZinthAbstract:Transient absorption experiments with probing in the blue part of the spectrum (440−500 nm) are performed for the electron-transfer system oxazine 1 in N,N-dimethylaniline. The experiments with high time resolution of better than 20 fs show pronounced modulations due to high-frequency wave packet motion (600 cm -1) in the excited electronic state of the oxazine 1 molecule before electron transfer. Additionally, modulations due to wave packet motion in the product state of oxazine 1 after complete charge separation are observed. The absorption transients related to the electron transfer from N,N-dimethylaniline to oxazine 1 are clearly nonmonoexponential with time constants of 30 and 80 fs. This behavior points to a strong adiabaticity of the electron-transfer reaction with a high relevance of nuclear motions.
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Modulation of Ultrafast Electron Transfer Dynamics by Wavepacket Motion in Oxazine 1
Springer Series in Chemical Physics, 1998Co-Authors: S. Engleitner, M. Seel, B. Wolfseder, Gerhard Stock, Wolfgang Domcke, Wolfgang ZinthAbstract:Experiments with highest temporal resolution on the electron transfer in oxazine 1 show pronounced nonexponential reaction dynamics and wavepacket motion in the reaction product.
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Wavepacket motion and ultrafast electron transfer in the system oxazine 1 in N,N-dimethylaniline
Chemical Physics Letters, 1997Co-Authors: M. Seel, S. Engleitner, Wolfgang ZinthAbstract:Abstract Femtosecond experiments on the oxazine 1 in N,N-dimethylaniline electron transfer system have been performed with a cross-correlation width of less than 18 fs. The experiments exhibit two different ultrafast absorption changes: a fast decay of the transmission occurs on the 30–80 fs timescale. This feature is assigned to an extremely fast electron transfer. Superimposed on these kinetics, assigned to the electron transfer, are strong oscillations arising from the wavepacket motion on the ground and excited state electronic surfaces with frequencies of up to 18 THz.
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Wavepacket Motion Observed in an Ultrafast Electron Transfer System
Springer Series in Chemical Physics, 1996Co-Authors: Wolfgang Zinth, S. Engleitner, M. SeelAbstract:For a number of systems it has been shown that ultrafast electron transfer (ET) reactions can occur even faster than relevant medium reorganization and relaxation processes [1–3]. In this context, the role of specific reaction pathways and intramolecular vibrational modes becomes increasingly important. Here we want to present new experimental results for the well-known ET system oxazine 1 (OX) in N,N-dimethylaniline (DMA) recorded with highest time resolution. The data are compared to the reference system OX in 1-chloronaphtalene (1CN) having similar solvent properties (dipolemoment, dielectric constant, viscosity), however showing no ET.
