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Stefan Berger - One of the best experts on this subject based on the ideXlab platform.
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wittig reactions of moderate ylides with heteroaryl substituents at the Phosphorus Atom
Tetrahedron, 2005Co-Authors: Marco Ackermann, Stefan BergerAbstract:Abstract The influence of various heteroaryl substituents at the Phosphorus Atom to the stereoselectivity of Wittig reactions of allylic and benzylic ylides has been studied. In the case of nitrogen bearing heteroaromatic ligands at the phosphorous Atom of benzylidenephosphoranes high E-alkene selectivity's of up to 90:10 could be observed. NMR spectroscopic investigations revealed that substituents at the Phosphorus have influences on the reactivity of ylides as well as the stability of reaction intermediates. Indications for chelation of lithium ions with ylides could also be detected and will be discussed in this article.
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a wittig reaction with 2 furyl substituents at the Phosphorus Atom improved z selectivity and isolation of a stable oxaphosphetane intermediate
European Journal of Organic Chemistry, 2002Co-Authors: Marco Appel, Steffen Blaurock, Stefan BergerAbstract:Wittig reactions with ylides bearing one, two or three 2-furyl groups directly bound to the Phosphorus Atom have been studied. Greatly improved (Z)-alkene selectivities of up to 98:2 could be observed if 2-furyl groups were present. Monitoring of the reactions by NMR spectroscopy revealed only oxaphosphetane intermediates, which became more stable with increasing number of 2-furyl substituents bound to the Phosphorus Atom. Oxaphosphetane 10d, with three furyl groups, was successfully isolated, and the results of a crystal structure analysis are presented. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)
Hidehiko Kodama - One of the best experts on this subject based on the ideXlab platform.
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a strategy for the stereoselective preparation of thymidine phosphorothioates with the r or the s configuration at the stereogenic Phosphorus Atom and their application to the synthesis of oligodeoxyribonucleotides with stereochemically pure phosphat
European Journal of Organic Chemistry, 2006Co-Authors: Yoshihiro Hayakawa, Yoshiko Hirabayashi, Mamoru Hyodo, Satoko Yamashita, Tomoyuki Matsunami, Rie Kawai, Hidehiko KodamaAbstract:This paper describes a new method for the highly stereoselective preparation of dithymidine phosphorothioates (TpsT) with the (R) or the (S) configuration at the stereogenic Phosphorus Atom [(Rp)- or (Sp)-TpsT, respectively], together with the synthesis of oligodeoxyribonucleotides with stereochemically pure phosphate/phosphorothioate mixed backbones through the use of (Rp)- or (Sp)-TpsT as building blocks.Stereochemically pure (Rp)- or (Sp)-TpsT was produced through a five-step process: 1) 1H-tetrazole-promoted thermodynamic equilibration of a diastereomeric mixture of allyl (Rp)- and (Sp)-thymidine 3′,5′-cyclic phosphate to give the (Sp) isomer as the major component, 2) stereospecific sulfurization of the allyl (Sp)-thymidine 3′,5′-cyclic phosphate to afford an allyl (Rp)-thymidine 3′,5′-cyclic phosphorothioate, 3) regioselective and stereoselective methanolysis of the allyl (Rp)-thymidine 3′,5′-cyclic phosphorothioate to provide an allyl methyl (Rp)-thymidine 3′-phosphorothioate as the main product, 4) stereospecific removal of the methyl group from the phosphorothioate moiety to give an allyl (Rp)-5′-O-dimethoxytritylthymidine 3′-phosphorothioate diester, or stereospecific removal of the allyl group from the phosphate moiety to form a methyl (Sp)-5′-O-dimethoxytritylthymidine 3′-phosphorothioate diester, and 5) stereospecific condensation of these (Rp)- and (Sp)-diesters with a 5′-O-free thymidine in a Mitsunobu reaction to produce the allyl (3′–5′)-linked (Sp)-dithymidine phosphorothioate and the methyl (3′–5′)-linked (Rp)-dithymidine phosphorothioate, respectively. The resulting (Rp)- and (Sp)-dithymidine phosphorothioates were converted into their 3′-phosphoramidites. Oligodeoxyribonucleotides with stereochemically pure phosphate/phosphorothioate-mixed backbones were then synthesized by use of these phosphoramidites as building blocks. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Vera Thelen - One of the best experts on this subject based on the ideXlab platform.
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The First Delocalized Phosphole Containing a Planar Tricoordinate Phosphorus Atom: 1‐[Bis(trimethylsilyl)methyl]‐3,5‐bis(trimethylsilyl)‐1,2,4‐triphosphole
Angewandte Chemie, 1998Co-Authors: F. Geoffrey N. Cloke, Peter B. Hitchcock, Philip Hunnable, John F. Nixon, László Nyulászi, Edgar Niecke, Vera ThelenAbstract:The sterically demanding groups on the tricoordinate Phosphorus Atom, the π-electron acceptors substituted on the ring, and the dicoordinate Phosphorus Atoms within the ring are the most significant factors contributing to the planarity and aromaticity of the 1,2,4-triphosphole ring in 1. The Bird aromaticity index for 1 shows that it has the most pronounced aromatic character of all known phospholes.
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the first delocalized phosphole containing a planar tricoordinate Phosphorus Atom 1 bis trimethylsilyl methyl 3 5 bis trimethylsilyl 1 2 4 triphosphole
Angewandte Chemie, 1998Co-Authors: Geoffrey F N Cloke, Peter B. Hitchcock, Philip Hunnable, John F. Nixon, László Nyulászi, Edgar Niecke, Vera ThelenAbstract:The sterically demanding groups on the tricoordinate Phosphorus Atom, the π-electron acceptors substituted on the ring, and the dicoordinate Phosphorus Atoms within the ring are the most significant factors contributing to the planarity and aromaticity of the 1,2,4-triphosphole ring in 1. The Bird aromaticity index for 1 shows that it has the most pronounced aromatic character of all known phospholes.
V I Sokolov - One of the best experts on this subject based on the ideXlab platform.
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change of the coordination type for the phospholyl ligand under nucleophilic attack of h2o on Phosphorus Atom in 2 5 diphenylphosphacymantrene promoted by aliphatic amines
Inorganica Chimica Acta, 2011Co-Authors: A G Ginzburg, Pavel V. Petrovskii, V V Bashilov, Fedor M Dolgushin, Alexander F Smolyakov, V I SokolovAbstract:Abstract η5-2,5-Diphenylphosphacymantrene (1) in benzene or CH2Cl2 solution does not react with amines. However, with amines NHEt2, NEt3, NEt(i-Pr)2 in excess and in the presence of small amounts of water 1 reacts to form anionic complexes [(CO)3Mn(η4-Ph2H2C4P( O)H]− A+, where cation A = H 2 NEt 2 + (2a), HNEt 3 + (2b), HN(Et) ( Pr i ) 2 + (2c). Probably, first an unstable intermediate with Р–ОН bond is formed as a result of the attack by the activated H2O molecule at the P Atom. Afterwards, the rapid rearrangement occurs with migration of H from O to P which leads to the ligand 2,5-diphenyl-1-Н-phosphol-1-oxide, Ph2H2C4P( O)H. Salts 2а–с have been characterized by 1H, 31P, 13C NMR- and IR-spectra and the structures of 2a and 2c established by single crystal X-ray diffraction analyses. The phosphoryl ligand in anions 2a and 2c has the “envelope” conformation and is η4-coordinated with Mn(CO)3. The Phosphorus Atom is not involved in the coordination with Mn because the Mn–P distances (2.7670(4) and 2.7732(8) A) are greater than the sum of covalent radii of P and Mn.
Marco Ackermann - One of the best experts on this subject based on the ideXlab platform.
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wittig reactions of moderate ylides with heteroaryl substituents at the Phosphorus Atom
Tetrahedron, 2005Co-Authors: Marco Ackermann, Stefan BergerAbstract:Abstract The influence of various heteroaryl substituents at the Phosphorus Atom to the stereoselectivity of Wittig reactions of allylic and benzylic ylides has been studied. In the case of nitrogen bearing heteroaromatic ligands at the phosphorous Atom of benzylidenephosphoranes high E-alkene selectivity's of up to 90:10 could be observed. NMR spectroscopic investigations revealed that substituents at the Phosphorus have influences on the reactivity of ylides as well as the stability of reaction intermediates. Indications for chelation of lithium ions with ylides could also be detected and will be discussed in this article.