The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform

Carl H Schiesser - One of the best experts on this subject based on the ideXlab platform.

  • intramolecular homolytic translocation chemistry an ab initio study of 1 n silyl germyl and Stannyl Group transfer and related ring closure reactions
    Journal of Organic Chemistry, 2003
    Co-Authors: Hiroshi Matsubara, Carl H Schiesser
    Abstract:

    Ab initio calculations using 6-311G**, cc-pVDZ, aug-cc-pVDZ, and a (valence) double-ζ pseudopotential (DZP) basis set, with (MP2, QCISD, CCSD(T)) and without (UHF) the inclusion of electron correla...

  • intramolecular homolytic translocation chemistry an ab initio study of 1 n silyl germyl and Stannyl Group transfer and related ring closure reactions
    Journal of Organic Chemistry, 2003
    Co-Authors: Hiroshi Matsubara, Carl H Schiesser
    Abstract:

    Ab initio calculations using 6-311G**, cc-pVDZ, aug-cc-pVDZ, and a (valence) double-zeta pseudopotential (DZP) basis set, with (MP2, QCISD, CCSD(T)) and without (UHF) the inclusion of electron correlation, and density functional methods (B3LYP) predict that 1,n-homolytic transfers (n = 1-5) of silyl, germyl, and Stannyl Groups from Group IV heteroatoms to carbon radicals can proceed via a frontside attack mechanism. At the B3LYP/DZP level of theory, energy barriers (DeltaE++) of 101.2, 98.8, 58.9, and 63.4 kJ/mol are calculated for the 1,2-, 1,3-, 1,4-, and 1,5-translocation reactions, respectively, of SiH3 between silicon atoms. Similar results are obtained for reactions involving germanium and tin with energy barriers (DeltaE++) of 85.9-113.1, 84.4-109.0, 41.7-73.3, and 48.5-78.2 kJ/mol for the 1,2-, 1,3-, 1,4-, and 1,5-translocation reactions, respectively. This study also predicts that four- and five-membered ring-closure reactions can be competitive with the 1,4- and 1,5-translocation reactions. These results suggest that while 1,2- and 1,3-translocation four-membered ring-formation reactions are unlikely to be synthetically viable, 1,4- and 1,5-transfers and five-membered ring-formation have synthetic possibilities.

Wilhelm P. Neumann - One of the best experts on this subject based on the ideXlab platform.

  • Tin for Organic Synthesis, 14. Synthesis of Aromatic and α,β‐Unsaturated Aldehydes by a Friedel‐Crafts‐like Electrophilic DeStannylation Using 1,1‐Dichloromethyl Methyl Ether
    Chemische Berichte, 1996
    Co-Authors: Michael Niestroj, Wilhelm P. Neumann
    Abstract:

    A mild and effective method for the preparation of a variety of aromatic (7a–m), heteroaromatic (7n–r), and α,β-unsaturated aldehydes (8a–f) is described. The reaction of trialkylaryl- (2a–o), heteroaryl- (2p–t), and 1-alkenylstannanes (4a–f and 5a–f) with dichloromethyl methyl ether (1, DCME) in the presence of aluminium trichloride followed by hydrolysis provides the corresponding aldehydes. In the case of arylstannanes the ipso-isomers are generally formed; the p-alde-hydes occur as side products. The electrophilic substitution of 1-alkenylstannanes with 1 leads to α,β-unsaturated aldehydes in an ipso- and stereospecific manner. A comparison of the leaving abilities of the Stannyl and silyl Groups shows a lower or even zero reactivity of the silyl-substituted compounds 6a–c towards the electrophile 1. In the silylStannylal-kene 6c only the Stannyl Group reacts whereas the Stannyl function remains unaffected in the product, aldehyde 11.

  • Tin for organic synthesis. 10. Unconventional regiospecific syntheses of aromatic carbonamides and thiocarbonamides by means of tin-mediated Friedel-Crafts reactions
    The Journal of Organic Chemistry, 1993
    Co-Authors: Martin Arnswald, Wilhelm P. Neumann
    Abstract:

    Friedel-Crafts reactions of Stannylarenes 1 with tosyl isocyanate (TsNCO, 2) give N-tosylcarbonamides 3 via ipso substitution of the Stannyl Group. Thus, unconventionally substituted aromatic carbonamides can be obtained. The combination of the reaction of 1 and 2 with that of 1 and chlorosulfonyl isocyanate (14) allows one-pot syntheses of N-(arylsulfonyl)-substituted aromatic carbonamides with optional substitution patterns on both aromatic rings. The known ipso-specific substitutions of Stannylarenes with 14 are extended to bi- and tricyclic arenes as well as to thiophenes 6 and 22. One Stannyl Group can serve as a leaving Group for two aromatic systems, as shown with diaryldialkyltins 29. Also, Stannylalkanes such as 27 react with 14 to afford alkylsulfonyl isocyanates and products of further reactions, such as 28. From the reactions of 1 with ethoxycarbonyl isothiocyanate (32), ortho- and meta-substituted aromatic thiocarbonamides 33 which are potential precursors for further syntheses, are accessible. The scope, limitations, and mechanism of these electrophilic substitutions are outlined

  • Tin for Organic Synthesis, 7. New Regioselective Syntheses of Diaryl Sulfones, Arenesulfonamides, and Arenesulfonic Acid Sodium Salts
    Chemische Berichte, 1993
    Co-Authors: Wilhelm P. Neumann, Christian Wicenec
    Abstract:

    The reaction of (trialkylStannyl)arenes 1 with corresponding reagents containing a chlorosulfonyl Group leads, by exclusive ipso substitution, to important diaryl sulfones 2a – i, N1-alkyl-arenesulfonamides 8a – f, and sodium arenesulfonates 13a – c in high yields under mild conditions. The specific leaving ability of the Stannyl Group allows, moreover, the preparation of arylsulfonyl isomers which are not accessible under the influence of the conventional directing forces of substituents. With N, N1-dialkylamidosulfonyl chloride/AlCl3 complexes no deStannylation takes place, but the first intramolecular sulfonyltin complex 11 is formed. This result is used to discuss details of the mechanism involved.

  • Tin for Organic Synthesis, 5 A New and Regioselective Synthesis of Aromatic Diazene Derivatives
    Chemische Berichte, 1991
    Co-Authors: Wilhelm P. Neumann, Christian Wicenec
    Abstract:

    A new method for the preparation of aromatic diazene derivatives 3a — 1, 5, 7a, b, 9 under very mild conditions is described. The reaction of trialkylarylstannanes with nitro-substituted benzenediazonium tetrafluoroborates leads, by strict ipso substitution, to the corresponding diaryldiazenes in satisfactory to high yields. Due to the excellent leaving Group quality of the Stannyl Group azo compounds may be prepared which are not accessible by normal electrophilic azo coupling. The products can be valuable precursors, obtained by reduction to the amines or other derivatizations, for consecutive aromatic compounds.

Hiromichi Tanaka - One of the best experts on this subject based on the ideXlab platform.

  • radical mediated Stannylation of vinyl sulfones access to novel 4 modified neplanocin a analogues
    Tetrahedron, 2009
    Co-Authors: Hiroki Kumamoto, Kazuki Deguchi, Tadashi Wagata, Yuu Furuya, Yuki Odanaka, Yukio Kitade, Hiromichi Tanaka
    Abstract:

    Abstract Synthesis of 4′-substituted (halogeno, phenyl, ethynyl, and cyano) neplanocin A analogues was carried out. A cyclopentenol derivative having a vinylstannane structure was designed as key-intermediate in this study, which was prepared based on radical-mediated sulfur-extrusive Stannylation. The resulting Stannylated cyclopentenol 15 was successfully condensed with 6-chloropurine through the Mitsunobu reaction, leading to the carbocyclic nucleoside 20 . Compound 20 was converted to its adenine counterpart 21 by treatment with NH 3 /MeOH, during which the 4′-Stannyl Group remained intact. The title compounds were prepared by using 21 or the 4′-iodo derivative ( 22 ) mostly through the Stille reaction.

  • Radical-mediated Stannylation of vinyl sulfones: access to novel 4′-modified neplanocin A analogues
    Tetrahedron, 2009
    Co-Authors: Hiroki Kumamoto, Kazuki Deguchi, Tadashi Wagata, Yuu Furuya, Yuki Odanaka, Yukio Kitade, Hiromichi Tanaka
    Abstract:

    Abstract Synthesis of 4′-substituted (halogeno, phenyl, ethynyl, and cyano) neplanocin A analogues was carried out. A cyclopentenol derivative having a vinylstannane structure was designed as key-intermediate in this study, which was prepared based on radical-mediated sulfur-extrusive Stannylation. The resulting Stannylated cyclopentenol 15 was successfully condensed with 6-chloropurine through the Mitsunobu reaction, leading to the carbocyclic nucleoside 20 . Compound 20 was converted to its adenine counterpart 21 by treatment with NH 3 /MeOH, during which the 4′-Stannyl Group remained intact. The title compounds were prepared by using 21 or the 4′-iodo derivative ( 22 ) mostly through the Stille reaction.

  • sulfoxide metal exchange for the synthesis of the 2 tributylStannyl derivative of 2 3 didehydro 2 3 dideoxyuridine d4u a general entry to 2 carbon substituted analogues of d4u
    Nucleosides Nucleotides & Nucleic Acids, 2002
    Co-Authors: Hiroki Kumamoto, Hiromichi Tanaka, Sayoko Onuma, Kumiko Tsuchiya, Yuko Egusa, Tsuyoshi Satoh
    Abstract:

    ABSTRACT Methods are described for the synthesis of the 2′-tributylStannyl derivative of 2′,3′-didehydro-2′, 3′-dideoxyuridine (d4U). Two approaches were investigated: radical-mediated desulfonylative Stannylation of the 2′-benzenesulfonyl derivative of d4U and sulfoxide-metal exchange reaction of the 2′-benzenesulfinyl derivative. The latter approach was found to give the desired 2′-Stannyl derivative in good yield. It was also shown that manipulations of the Stannyl Group allowed the introduction of a variety of carbon-substituents to the 2′-position by applying the Stille reaction. The whole reaction sequence has opened up a highly general entry to 2′-carbon-substituted analogues of d4U.

  • an intramolecular anionic migration of a Stannyl Group from the 6 position of 1 2 deoxy d erythro pent 1 enofuranosyl uracil to the 2 position synthesis of 2 substituted 1 2 unsaturated uridines
    Tetrahedron, 2000
    Co-Authors: Hiroki Kumamoto, Hiromichi Tanaka, Satoru Shindoh, Yoshiharu Itoh, Kazuhiro Haraguchi, Atsushi Kittaka, Tadashi Miyasaka, Masato Kondo, Kazuo T Nakamura
    Abstract:

    Abstract Lithiation of 1-[3,5-bis-O-(tert-butyldimethylsilyl)-2-deoxy- d -erythro-pent-1-enofuranosyl)uracil (1) takes place exclusively at the 6-position of the uracil base. The 6-tributylStannyl (or 6-trimethylsilyl) derivative prepared by quenching the C6-lithiated species with Bu3SnCl (or Me3SiCl) was found to undergo an intramolecular anionic migration to the 2′-positon of the furanoid glycal portion. By manipulation of the 2′-Stannyl Group, 2′-halogeno and 2′-carbon-substituted 1′,2′-unsaturated uridines were prepared for the first time. In contrast to the reported instability of 1 during deprotection, the 2′-substituted analogs synthesized in the present study gave the corresponding free nucleosides uniformly in high yields upon treatment with NH4F in MeOH.

  • An Intramolecular Anionic Migration of a Stannyl Group from the 6-Position of 1-(2-Deoxy-d-erythro-pent-1-enofuranosyl)uracil to the 2′-Position: Synthesis of 2′-Substituted 1′,2′-Unsaturated Uridines
    Tetrahedron, 2000
    Co-Authors: Hiroki Kumamoto, Hiromichi Tanaka, Satoru Shindoh, Yoshiharu Itoh, Kazuhiro Haraguchi, Atsushi Kittaka, Tadashi Miyasaka, Masato Kondo, Eisen Gen, Kazuo T Nakamura
    Abstract:

    Abstract Lithiation of 1-[3,5-bis-O-(tert-butyldimethylsilyl)-2-deoxy- d -erythro-pent-1-enofuranosyl)uracil (1) takes place exclusively at the 6-position of the uracil base. The 6-tributylStannyl (or 6-trimethylsilyl) derivative prepared by quenching the C6-lithiated species with Bu3SnCl (or Me3SiCl) was found to undergo an intramolecular anionic migration to the 2′-positon of the furanoid glycal portion. By manipulation of the 2′-Stannyl Group, 2′-halogeno and 2′-carbon-substituted 1′,2′-unsaturated uridines were prepared for the first time. In contrast to the reported instability of 1 during deprotection, the 2′-substituted analogs synthesized in the present study gave the corresponding free nucleosides uniformly in high yields upon treatment with NH4F in MeOH.

Hiroshi Matsubara - One of the best experts on this subject based on the ideXlab platform.

  • intramolecular homolytic translocation chemistry an ab initio study of 1 n silyl germyl and Stannyl Group transfer and related ring closure reactions
    Journal of Organic Chemistry, 2003
    Co-Authors: Hiroshi Matsubara, Carl H Schiesser
    Abstract:

    Ab initio calculations using 6-311G**, cc-pVDZ, aug-cc-pVDZ, and a (valence) double-ζ pseudopotential (DZP) basis set, with (MP2, QCISD, CCSD(T)) and without (UHF) the inclusion of electron correla...

  • intramolecular homolytic translocation chemistry an ab initio study of 1 n silyl germyl and Stannyl Group transfer and related ring closure reactions
    Journal of Organic Chemistry, 2003
    Co-Authors: Hiroshi Matsubara, Carl H Schiesser
    Abstract:

    Ab initio calculations using 6-311G**, cc-pVDZ, aug-cc-pVDZ, and a (valence) double-zeta pseudopotential (DZP) basis set, with (MP2, QCISD, CCSD(T)) and without (UHF) the inclusion of electron correlation, and density functional methods (B3LYP) predict that 1,n-homolytic transfers (n = 1-5) of silyl, germyl, and Stannyl Groups from Group IV heteroatoms to carbon radicals can proceed via a frontside attack mechanism. At the B3LYP/DZP level of theory, energy barriers (DeltaE++) of 101.2, 98.8, 58.9, and 63.4 kJ/mol are calculated for the 1,2-, 1,3-, 1,4-, and 1,5-translocation reactions, respectively, of SiH3 between silicon atoms. Similar results are obtained for reactions involving germanium and tin with energy barriers (DeltaE++) of 85.9-113.1, 84.4-109.0, 41.7-73.3, and 48.5-78.2 kJ/mol for the 1,2-, 1,3-, 1,4-, and 1,5-translocation reactions, respectively. This study also predicts that four- and five-membered ring-closure reactions can be competitive with the 1,4- and 1,5-translocation reactions. These results suggest that while 1,2- and 1,3-translocation four-membered ring-formation reactions are unlikely to be synthetically viable, 1,4- and 1,5-transfers and five-membered ring-formation have synthetic possibilities.

Hiroki Kumamoto - One of the best experts on this subject based on the ideXlab platform.

  • radical mediated Stannylation of vinyl sulfones access to novel 4 modified neplanocin a analogues
    Tetrahedron, 2009
    Co-Authors: Hiroki Kumamoto, Kazuki Deguchi, Tadashi Wagata, Yuu Furuya, Yuki Odanaka, Yukio Kitade, Hiromichi Tanaka
    Abstract:

    Abstract Synthesis of 4′-substituted (halogeno, phenyl, ethynyl, and cyano) neplanocin A analogues was carried out. A cyclopentenol derivative having a vinylstannane structure was designed as key-intermediate in this study, which was prepared based on radical-mediated sulfur-extrusive Stannylation. The resulting Stannylated cyclopentenol 15 was successfully condensed with 6-chloropurine through the Mitsunobu reaction, leading to the carbocyclic nucleoside 20 . Compound 20 was converted to its adenine counterpart 21 by treatment with NH 3 /MeOH, during which the 4′-Stannyl Group remained intact. The title compounds were prepared by using 21 or the 4′-iodo derivative ( 22 ) mostly through the Stille reaction.

  • Radical-mediated Stannylation of vinyl sulfones: access to novel 4′-modified neplanocin A analogues
    Tetrahedron, 2009
    Co-Authors: Hiroki Kumamoto, Kazuki Deguchi, Tadashi Wagata, Yuu Furuya, Yuki Odanaka, Yukio Kitade, Hiromichi Tanaka
    Abstract:

    Abstract Synthesis of 4′-substituted (halogeno, phenyl, ethynyl, and cyano) neplanocin A analogues was carried out. A cyclopentenol derivative having a vinylstannane structure was designed as key-intermediate in this study, which was prepared based on radical-mediated sulfur-extrusive Stannylation. The resulting Stannylated cyclopentenol 15 was successfully condensed with 6-chloropurine through the Mitsunobu reaction, leading to the carbocyclic nucleoside 20 . Compound 20 was converted to its adenine counterpart 21 by treatment with NH 3 /MeOH, during which the 4′-Stannyl Group remained intact. The title compounds were prepared by using 21 or the 4′-iodo derivative ( 22 ) mostly through the Stille reaction.

  • sulfoxide metal exchange for the synthesis of the 2 tributylStannyl derivative of 2 3 didehydro 2 3 dideoxyuridine d4u a general entry to 2 carbon substituted analogues of d4u
    Nucleosides Nucleotides & Nucleic Acids, 2002
    Co-Authors: Hiroki Kumamoto, Hiromichi Tanaka, Sayoko Onuma, Kumiko Tsuchiya, Yuko Egusa, Tsuyoshi Satoh
    Abstract:

    ABSTRACT Methods are described for the synthesis of the 2′-tributylStannyl derivative of 2′,3′-didehydro-2′, 3′-dideoxyuridine (d4U). Two approaches were investigated: radical-mediated desulfonylative Stannylation of the 2′-benzenesulfonyl derivative of d4U and sulfoxide-metal exchange reaction of the 2′-benzenesulfinyl derivative. The latter approach was found to give the desired 2′-Stannyl derivative in good yield. It was also shown that manipulations of the Stannyl Group allowed the introduction of a variety of carbon-substituents to the 2′-position by applying the Stille reaction. The whole reaction sequence has opened up a highly general entry to 2′-carbon-substituted analogues of d4U.

  • an intramolecular anionic migration of a Stannyl Group from the 6 position of 1 2 deoxy d erythro pent 1 enofuranosyl uracil to the 2 position synthesis of 2 substituted 1 2 unsaturated uridines
    Tetrahedron, 2000
    Co-Authors: Hiroki Kumamoto, Hiromichi Tanaka, Satoru Shindoh, Yoshiharu Itoh, Kazuhiro Haraguchi, Atsushi Kittaka, Tadashi Miyasaka, Masato Kondo, Kazuo T Nakamura
    Abstract:

    Abstract Lithiation of 1-[3,5-bis-O-(tert-butyldimethylsilyl)-2-deoxy- d -erythro-pent-1-enofuranosyl)uracil (1) takes place exclusively at the 6-position of the uracil base. The 6-tributylStannyl (or 6-trimethylsilyl) derivative prepared by quenching the C6-lithiated species with Bu3SnCl (or Me3SiCl) was found to undergo an intramolecular anionic migration to the 2′-positon of the furanoid glycal portion. By manipulation of the 2′-Stannyl Group, 2′-halogeno and 2′-carbon-substituted 1′,2′-unsaturated uridines were prepared for the first time. In contrast to the reported instability of 1 during deprotection, the 2′-substituted analogs synthesized in the present study gave the corresponding free nucleosides uniformly in high yields upon treatment with NH4F in MeOH.

  • An Intramolecular Anionic Migration of a Stannyl Group from the 6-Position of 1-(2-Deoxy-d-erythro-pent-1-enofuranosyl)uracil to the 2′-Position: Synthesis of 2′-Substituted 1′,2′-Unsaturated Uridines
    Tetrahedron, 2000
    Co-Authors: Hiroki Kumamoto, Hiromichi Tanaka, Satoru Shindoh, Yoshiharu Itoh, Kazuhiro Haraguchi, Atsushi Kittaka, Tadashi Miyasaka, Masato Kondo, Eisen Gen, Kazuo T Nakamura
    Abstract:

    Abstract Lithiation of 1-[3,5-bis-O-(tert-butyldimethylsilyl)-2-deoxy- d -erythro-pent-1-enofuranosyl)uracil (1) takes place exclusively at the 6-position of the uracil base. The 6-tributylStannyl (or 6-trimethylsilyl) derivative prepared by quenching the C6-lithiated species with Bu3SnCl (or Me3SiCl) was found to undergo an intramolecular anionic migration to the 2′-positon of the furanoid glycal portion. By manipulation of the 2′-Stannyl Group, 2′-halogeno and 2′-carbon-substituted 1′,2′-unsaturated uridines were prepared for the first time. In contrast to the reported instability of 1 during deprotection, the 2′-substituted analogs synthesized in the present study gave the corresponding free nucleosides uniformly in high yields upon treatment with NH4F in MeOH.