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Hans-ulrich Reissig - One of the best experts on this subject based on the ideXlab platform.
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samarium diiodide promoted reduction of 3 6 dihydro 2h 1 2 Oxazines competition of 1 4 amino alcohol formation and ring contraction to pyrrole derivatives
European Journal of Organic Chemistry, 2013Co-Authors: Marcin Jasinski, Toshiko Watanabe, Hans-ulrich ReissigAbstract:An approach to enantiopure 1,4-amino alcohols of type 4 by samarium diiodide mediated N–O cleavage of 3,6-dihydro-2H-1,2-Oxazines 3 is presented. In several cases we observed the formation of 3-methoxypyrrole derivatives 5 as byproducts in significant amounts. For 1,2-Oxazine derivative syn-3a, up to 27 % of pyrrole 5a was isolated. The examples presented show a strong dependence of the chemoselectivity on the structure of the precursor 1,2-Oxazines. The formation of pyrroles 5 as side-products is rationalized by a competitive intramolecular hydrogen shift of the initially formed ring cleavage intermediate B to C and subsequent cyclization of aldehyde E to afford F. This pathway can be disfavoured when a higher excess of samarium diiodide was employed, which generally provided the 1,4-amino alcohols 4 in good yields.
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application of l erythrose derived nitrones in the synthesis of polyhydroxylated compounds via 3 6 dihydro 2h 1 2 Oxazine derivatives
European Journal of Organic Chemistry, 2012Co-Authors: Marcin Jasinski, Dieter Lentz, Elena Morenoclavijo, Hans-ulrich ReissigAbstract:Enantiopure 3,6-dihydro-2H-1,2-Oxazines were prepared by [3+3] cyclisations starting from lithiated methoxyallene and the L-erythrose-derived nitrones 1′ and 3. The role of the side-chain protective group, which steers the highly selective formation of either anti- or syn-configured products, was demonstrated. A hydroboration/oxidation protocol smoothly converted 1,2-Oxazine derivative syn-5 into secondary alcohol 6. After deprotection, polyhydroxylated tetrahydro-2H-1,2-Oxazine 11, which can be regarded as an azasugar, was isolated. Analogous treatment of 1,2-Oxazine anti-5 with the borane not only provided the expected secondary alcohol 7, but it also induced reduction of the C=C bond and ring opening. Treatment of syn-5 and anti-2 with hydrochloric acid in methanol induced deprotections and cyclisations leading to bicyclic tetrahydro-2H-1,2-Oxazine derivatives. The second ring can be either a furan or a pyran ring. In the syn series, furan derivative 12 was formed exclusively, and its hydrogenolysis led to enantiopure aminofuran derivative 14. Acid-promoted rearrangement of unprotected anti-2 led to a mixture of bicyclic compounds with furan or pyran rings fused to the 1,2-Oxazine core. However, when TBDPS-protected compound 20 was used it cleanly led to 1,2-Oxazine 21 with a fused furan ring and then to aminofuran 22. Alternatively, the N–O bond in unprotected anti-2 was chemoselectively reduced with samarium diiodide, efficiently generating highly functionalized allylic alcohol 23. Acid-promoted cyclisation and deprotection furnished furan derivative 24. Mechanistic suggestions to explain the different outcomes of the acid-induced transformations are provided. Overall, it is demonstrated that the stereodivergent addition of lithiated alkoxyallenes to L-erythrose-derived nitrones allow flexible access to a series of enantiopure amino polyols, including aminofuran derivatives.
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synthesis of novel carbohydrate mimetics via 1 2 Oxazines
Pure and Applied Chemistry, 2011Co-Authors: Lea Bouche, Hans-ulrich ReissigAbstract:The combination of lithiated alkoxyallenes with carbohydrate-derived nitrones con- stitutes a flexible entry to highly functionalized enantiopure 1,2-Oxazine derivatives. They can be used as precursors for acyclic and cyclic carbohydrate-like products such as amino sugar alcohols, azetidine and pyrrolidine derivatives. The Lewis acid-promoted rearrange- ment of 1,3-dioxolanyl-substituted 1,2-Oxazines to bicyclic compounds allows an efficient route to novel amino pyran and oxepane derivatives. After subsequent transformations, new carbohydrate mimetics or "real" carbohydrates were obtained in good yield and often in a stereodivergent fashion. These compounds have already been employed for the preparation of unusual di- and trisaccharide derivatives. Several of the products prepared showed inter- esting biological activities, e.g., as L- and P-selectin inhibitors with IC 50 values in the sub- nanomolar range.
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Palladium-catalyzed cross coupling reactions of 4-bromo-6H-1,2-Oxazines
Beilstein Journal of Organic Chemistry, 2009Co-Authors: Reinhold Zimmer, Elmar Schmidt, Michal Sascha Andrä, Marcel-antoine Duhs, Igor Linder, Hans-ulrich ReissigAbstract:A number of 4-aryl- and 4-alkynyl-substituted 6H-1,2-Oxazines 8 and 9 have been prepared in good yields via cross coupling reactions of halogenated precursors 2, which in turn are easily accessible by bromination of 6H-1,2-Oxazines 1. Lewis-acid promoted reaction of 1,2-Oxazine 9c with 1-hexyne provided alkynyl-substituted pyridine derivative 12 thus demonstrating the potential of this approach for the synthesis of pyridines.
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a new access to pyrrolizidine derivatives ring contraction of methyl e 1 2 oxazin 3 yl propenoates
Synthesis, 2008Co-Authors: Reinhold Zimmer, Markus Collas, Regina Czerwonka, Ute Hain, Hans-ulrich ReissigAbstract:Nitrosoalkene 2 generated in situ from oxime 3 underwent smooth hetero Diels-Alder reaction with enol ethers 1 to afford 1,2-Oxazine derivatives 4 bearing an exocyclic C=C bond. Methoxyallene 8 and 2 provided 6 H-1,2-Oxazine 10 in good overall yield. The exocyclic double bond of this type of 1,2-Oxazines can be employed for addition reactions as demonstrated by dihydroxylation of 4A with potassium permanganate, smoothly delivering 1,2-diol 11. A reductive cascade reaction involving ring cleavage at the N-O bond followed by cyclization steps furnished pyrrolizidinone derivatives 12 in good yields. In the case of 12B this transformation proceeded with excellent stereoselectivity. Finally, the lactam moiety of 12 could be reduced with borane to provide the corresponding pyrrolizidine derivatives 19 in good yield.
Hatsuo Ishida - One of the best experts on this subject based on the ideXlab platform.
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Oxazine ring related vibrational modes of benzOxazine monomers using fully aromatically substituted deuterated 15n isotope exchanged and Oxazine ring substituted compounds and theoretical calculations
Journal of Physical Chemistry A, 2017Co-Authors: Lu Han, Daniela Iguchi, Tyler R. Heyl, Victoria M. Sedwick, Carlos R. Arza, Daniel J. Lacks, Phwey S Gil, Seishi Ohashi, Hatsuo IshidaAbstract:Polymerization of benzOxazine resins is indicated by the disappearance of a 960–900 cm–1 band in infrared spectroscopy (IR). Historically, this band was assigned to the C–H out-of-plane bending of the benzene to which the Oxazine ring is attached. This study shows that this band is a mixture of the O–C2 stretching of the Oxazine ring and the phenolic ring vibrational modes. Vibrational frequencies of 3-phenyl-3,4-dihydro-2H-benzo[e][1,3]Oxazine (PH-a) and 3-(tert-butyl)-3,4-dihydro-2H-benzo[e][1,3]Oxazine (PH-t) are compared with isotope-exchanged and all-substituted compounds. Deuterated benzOxazine monomers, 15N-isotope exchanged benzOxazine monomers, and all-substituted benzOxazine monomers without aromatic C–H groups are synthesized and studied meticulously. The various isotopic-exchanges involved deuteration around the benzene ring of phenol, selective deuteration of each CH2 in the O–CH2–N (2) and N–CH2–Ar (4) positions on the Oxazine ring, or simultaneous deuteration of both positions. The chemical...
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Oxazine Ring-Related Vibrational Modes of BenzOxazine Monomers Using Fully Aromatically Substituted, Deuterated, 15N Isotope Exchanged, and Oxazine-Ring-Substituted Compounds and Theoretical Calculations
2017Co-Authors: Lu Han, Daniela Iguchi, Phwey Gil, Tyler R. Heyl, Victoria M. Sedwick, Carlos R. Arza, Daniel J. Lacks, Hatsuo IshidaAbstract:Polymerization of benzOxazine resins is indicated by the disappearance of a 960–900 cm–1 band in infrared spectroscopy (IR). Historically, this band was assigned to the C–H out-of-plane bending of the benzene to which the Oxazine ring is attached. This study shows that this band is a mixture of the O–C2 stretching of the Oxazine ring and the phenolic ring vibrational modes. Vibrational frequencies of 3-phenyl-3,4-dihydro-2H-benzo[e][1,3]Oxazine (PH-a) and 3-(tert-butyl)-3,4-dihydro-2H-benzo[e][1,3]Oxazine (PH-t) are compared with isotope-exchanged and all-substituted compounds. Deuterated benzOxazine monomers, 15N-isotope exchanged benzOxazine monomers, and all-substituted benzOxazine monomers without aromatic C–H groups are synthesized and studied meticulously. The various isotopic-exchanges involved deuteration around the benzene ring of phenol, selective deuteration of each CH2 in the O–CH2–N (2) and N–CH2–Ar (4) positions on the Oxazine ring, or simultaneous deuteration of both positions. The chemical structures were confirmed by 1H nuclear magnetic resonance spectroscopy (1H NMR). The IR and Raman spectra of each compound are compared. Further analysis of 15N isotope-exchanged PH-a indicates the influence of the nitrogen isotope on the band position, both experimentally and theoretically. This finding is important for polymerization studies of benzOxazines that utilize vibrational spectroscopy
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use of allyl functional benzOxazine monomers as replacement for styrene in vinyl ester resins
Polymer International, 2013Co-Authors: Lin Jin, Tarek Agag, Hatsuo IshidaAbstract:New vinyl ester systems are prepared using allyl-functional benzOxazine monomers, 3-allyl-6-methyl-3,4-dihydro-2H-benzo[e][1,3]Oxazine (pC-ala) or bis(3-allyl-3,4-dihydro-2H-benzo[e][1,3]oxazin-6-yl)methane (BF-ala), as reactive diluents for vinyl ester resins derived from an epoxy resin, diglycidyl ether of bisphenol A, instead of using styrene. Different initiators are used to investigate the copolymerization of allyl function from pC-ala with vinyl function from vinyl ester resin prepolymer. The temperature dependence of viscosity is studied to demonstrate the retention of processability of the new vinyl ester resins. Dynamic mechanical and thermogravimetric analyses are used to investigate the dynamic mechanical properties and thermal stability of the new resins. Copyright © 2012 Society of Chemical Industry
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asymmetric mono Oxazine an inevitable product from mannich reaction of benzOxazine dimers
Journal of the American Chemical Society, 2001Co-Authors: Apirat Laobuthee, Suwabun Chirachanchai, Hatsuo Ishida, Kohji TashiroAbstract:The Mannich reaction is detailed, which was carried out on benzOxazine dimers under various conditions, that is, temperature, reaction time, and solvents. Against our expectation, in any condition, instead of generating a disubstitution Oxazine compound, the reaction gives a product with only a single Oxazine ring, a mono-Oxazine benzOxazine dimer, as characterized by FT-IR, 1H NMR, 13C NMR, 2D-NMR (1H−1H COSY, 1H−13C HMQC, and 1H−13C HMBC), and EA. The asymmetrical reaction is found to be based on the original structure of the benzOxazine dimer which has two phenol rings in a different stability as clarified by X-ray structure analysis of the single crystal. All types of benzOxazine dimers indicate the specific structure with a pair of inter- and intramolecular hydrogen bonds. The bond distance indicates that the intramolecular hydrogen bonding is very strong, while the packing structure emphasizes the high stability of the dimer unit and implies the deactivation of one phenol ring in the benzOxazine dim...
Marcin Jasinski - One of the best experts on this subject based on the ideXlab platform.
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samarium diiodide promoted reduction of 3 6 dihydro 2h 1 2 Oxazines competition of 1 4 amino alcohol formation and ring contraction to pyrrole derivatives
European Journal of Organic Chemistry, 2013Co-Authors: Marcin Jasinski, Toshiko Watanabe, Hans-ulrich ReissigAbstract:An approach to enantiopure 1,4-amino alcohols of type 4 by samarium diiodide mediated N–O cleavage of 3,6-dihydro-2H-1,2-Oxazines 3 is presented. In several cases we observed the formation of 3-methoxypyrrole derivatives 5 as byproducts in significant amounts. For 1,2-Oxazine derivative syn-3a, up to 27 % of pyrrole 5a was isolated. The examples presented show a strong dependence of the chemoselectivity on the structure of the precursor 1,2-Oxazines. The formation of pyrroles 5 as side-products is rationalized by a competitive intramolecular hydrogen shift of the initially formed ring cleavage intermediate B to C and subsequent cyclization of aldehyde E to afford F. This pathway can be disfavoured when a higher excess of samarium diiodide was employed, which generally provided the 1,4-amino alcohols 4 in good yields.
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application of l erythrose derived nitrones in the synthesis of polyhydroxylated compounds via 3 6 dihydro 2h 1 2 Oxazine derivatives
European Journal of Organic Chemistry, 2012Co-Authors: Marcin Jasinski, Dieter Lentz, Elena Morenoclavijo, Hans-ulrich ReissigAbstract:Enantiopure 3,6-dihydro-2H-1,2-Oxazines were prepared by [3+3] cyclisations starting from lithiated methoxyallene and the L-erythrose-derived nitrones 1′ and 3. The role of the side-chain protective group, which steers the highly selective formation of either anti- or syn-configured products, was demonstrated. A hydroboration/oxidation protocol smoothly converted 1,2-Oxazine derivative syn-5 into secondary alcohol 6. After deprotection, polyhydroxylated tetrahydro-2H-1,2-Oxazine 11, which can be regarded as an azasugar, was isolated. Analogous treatment of 1,2-Oxazine anti-5 with the borane not only provided the expected secondary alcohol 7, but it also induced reduction of the C=C bond and ring opening. Treatment of syn-5 and anti-2 with hydrochloric acid in methanol induced deprotections and cyclisations leading to bicyclic tetrahydro-2H-1,2-Oxazine derivatives. The second ring can be either a furan or a pyran ring. In the syn series, furan derivative 12 was formed exclusively, and its hydrogenolysis led to enantiopure aminofuran derivative 14. Acid-promoted rearrangement of unprotected anti-2 led to a mixture of bicyclic compounds with furan or pyran rings fused to the 1,2-Oxazine core. However, when TBDPS-protected compound 20 was used it cleanly led to 1,2-Oxazine 21 with a fused furan ring and then to aminofuran 22. Alternatively, the N–O bond in unprotected anti-2 was chemoselectively reduced with samarium diiodide, efficiently generating highly functionalized allylic alcohol 23. Acid-promoted cyclisation and deprotection furnished furan derivative 24. Mechanistic suggestions to explain the different outcomes of the acid-induced transformations are provided. Overall, it is demonstrated that the stereodivergent addition of lithiated alkoxyallenes to L-erythrose-derived nitrones allow flexible access to a series of enantiopure amino polyols, including aminofuran derivatives.
Wonhun Ham - One of the best experts on this subject based on the ideXlab platform.
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stereoselective total syntheses of castanospermine and neu5ac methyl ester
Journal of Organic Chemistry, 2019Co-Authors: In-soo Myeong, Yong-taek Lee, Jihun Kang, Wonhun HamAbstract:Concise and stereocontrolled total syntheses of (+)-castanospermine and N-acetylneuraminic acid methyl ester were achieved from diastereomerically enriched anti, syn, syn-1,3-Oxazine and anti, syn, anti-1,3-Oxazine, respectively. The key step in this strategy was the stereoselective BF3·OEt2-mediated allylation.
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Stereoselective Total Syntheses of (+)-Castanospermine and Neu5Ac Methyl Ester
2019Co-Authors: In-soo Myeong, Yong-taek Lee, Jihun Kang, Wonhun HamAbstract:Concise and stereocontrolled total syntheses of (+)-castanospermine and N-acetylneuraminic acid methyl ester were achieved from diastereomerically enriched anti,syn,syn-1,3-Oxazine and anti,syn,anti-1,3-Oxazine, respectively. The key step in this strategy was the stereoselective BF3·OEt2-mediated allylation
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asymmetric total syntheses of 2 5 dideoxy 2 5 imino d glucitol dgdp and 1 deoxymannojirimycin dmj via an extended chiral 1 3 Oxazine
Tetrahedron Letters, 2018Co-Authors: In-soo Myeong, Seok-hwi Park, Changyoung Jung, Jiyeon Kim, Wonhun HamAbstract:Abstract The asymmetric total syntheses of (+)-2,5-dideoxy-2,5-imino- d -glucitol [(+)-DGDP] 1 and (−)-1-deoxymannojirimycin [(−)-DMJ] 2 were achieved using an extended chiral 1,3-Oxazine. The key synthetic strategies included extension of the chirality of anti,syn-Oxazine 3 using diastereoselective dihydroxylation, and piperidine and pyrrolidine ring formation. Starting from readily available anti,syn-Oxazine 3, (+)-DGDP 1 was synthesized in 5 steps with 31.6% overall yield and (−)-DMJ 2 was synthesized in 4 steps with 60.6% overall yield.
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asymmetric total synthesis of conduramine a 1 via a chiral syn anti Oxazine
ChemInform, 2016Co-Authors: In-soo Myeong, Seok-hwi Park, Changyoung Jung, Jin Seok Kim, Yong-taek Lee, Jongcheol Kang, Wonhun HamAbstract:Abstract The total synthesis of (−)-conduramine A-1 was achieved by using a diastereomerically enriched syn , anti -Oxazine intermediate. The key steps in this strategy were the stereoselective extension of the chirality of syn , anti -Oxazine, a Wittig reaction, and a ring-closing metathesis reaction.
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1 3 Oxazine as a chiral building block used in the total synthesis of 1 deoxynojirimycin and 2r 5r dihydroxymethyl 3r 4r dihydroxypyrrolidine
Tetrahedron-asymmetry, 2015Co-Authors: Seok-hwi Park, Changyoung Jung, Dong-keun Song, Jiyeon Kim, Jin Seok Kim, Wonhun HamAbstract:Concise and stereocontrolled syntheses of (+)-1-deoxynojirimycin and (2R,5R)-dihydroxymethyl-(3R,4R)-dihydroxypyrrolidine [(+)-DMDP] were achieved via a diastereomerically enriched Oxazine intermediate. The key strategies include the use of 1,3-Oxazine as a chiral building block and diastereoselective nucleophilic addition to an aldehyde. Starting from readily available (R)-methyl 2-benzamido-3-((tert-butyldimethylsilyl)oxy)propanoate, (+)-1-deoxynojirimycin was synthesized in 11 steps and 26.2% overall yield while (+)-DMDP was synthesized in 11 steps and 27.1% overall yield, respectively.
Fumitoshi Shibahara - One of the best experts on this subject based on the ideXlab platform.
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n thioacyl 1 3 amino alcohols synthesis via ring opening of oxiranes with thioamide dianions and applications as key intermediates leading to stereochemically defined 5 6 dihydro 4h 1 3 Oxazines and 1 3 amino alcohols
Journal of Organic Chemistry, 2005Co-Authors: Toshiaki Murai, Hideo Aso, Hiroaki Sano, Hiroyasu Kawai, Fumitoshi ShibaharaAbstract:N-Thioacyl 1,3-amino alcohols were synthesized via the ring-opening of oxiranes with thioamide dianions generated from N-benzyl thioamides and BuLi in a highly regio- and stereoselective manner. The diastereomers of N-thioacyl 1,3-amino alcohols were readily separated by column chromatography to give stereochemically defined N-thioacyl 1,3-amino alcohols. They underwent intramolecular cyclization with Bu4F and EtI to give 5,6-dihydro-4H-1,3-Oxazines. The reaction was specific with anti-N-thioacyl 1,3-amino alcohols, and cis-5,6-dihydro-4H-1,3-Oxazines were obtained with high efficiency, whereas the reaction of a syn-alcohol gave a thioimidate as a major product. The reduction of N-thioacyl 1,3-amino alcohols with LiAlH4gave N-alkyl 1,3-amino alcohols in high yields. The use of optically active propylene oxide as a starting material gave the corresponding Oxazine and alcohols in optically pure forms.
