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Matthias Wagner - One of the best experts on this subject based on the ideXlab platform.
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steric shielding vs structural constraint in a boron containing polycyclic aromatic hydrocarbon
Organometallics, 2017Co-Authors: Valentin M Hertz, Naoki Ando, Masato Hirai, Michael Bolte, Hans-wolfram Lerner, Shigehiro Yamaguchi, Matthias WagnerAbstract:The highly reactive boron-doped polycyclic aromatic hydrocarbon 8H-8-bromo-8-borabenzo[gh]tetraphene has been synthesized via a multistep sequence encompassing a Peterson Olefination, a stilbene-type photocyclization, and an Si/B exchange reaction. The compound was subsequently treated with mesityllithium to give the derivative 3 or with [2,6-bis(propen-2-yl)phenyl]lithium to furnish the intermediate 4. A scandium(III) triflate mediated Friedel–Crafts reaction transformed 4 into the rigid, planarized triarylborane 5. Compounds 3 and 5 are both inert toward air and moisture but are still able to bind fluoride ions, where the affinity of 3 in CHCl3 is higher than that of 5. Both arylboranes are yellow solids, and their solutions exhibit an intense blue fluorescence (ΦPL = 85% (3), 89% (5)). According to cyclic voltammetry, reversible reduction occurs at half-wave potentials of E1/2 = −2.05 V (3) and −2.14 V (5; in THF, vs FcH/FcH+). The crystal lattices consist of π-stacked dimers, arranged in herringbone p...
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Steric Shielding vs Structural Constraint in a Boron-Containing Polycyclic Aromatic Hydrocarbon
2016Co-Authors: Valentin M. Hertz, Naoki Ando, Masato Hirai, Michael Bolte, Hans-wolfram Lerner, Shigehiro Yamaguchi, Matthias WagnerAbstract:The highly reactive boron-doped polycyclic aromatic hydrocarbon 8H-8-bromo-8-borabenzo[gh]tetraphene has been synthesized via a multistep sequence encompassing a Peterson Olefination, a stilbene-type photocyclization, and an Si/B exchange reaction. The compound was subsequently treated with mesityllithium to give the derivative 3 or with [2,6-bis(propen-2-yl)phenyl]lithium to furnish the intermediate 4. A scandium(III) triflate mediated Friedel–Crafts reaction transformed 4 into the rigid, planarized triarylborane 5. Compounds 3 and 5 are both inert toward air and moisture but are still able to bind fluoride ions, where the affinity of 3 in CHCl3 is higher than that of 5. Both arylboranes are yellow solids, and their solutions exhibit an intense blue fluorescence (ΦPL = 85% (3), 89% (5)). According to cyclic voltammetry, reversible reduction occurs at half-wave potentials of E1/2 = −2.05 V (3) and −2.14 V (5; in THF, vs FcH/FcH+). The crystal lattices consist of π-stacked dimers, arranged in herringbone patterns. Importantly, 3 and 5 share nearly identical properties, despite possessing fundamentally different structures
Israel Agranat - One of the best experts on this subject based on the ideXlab platform.
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Peterson Olefination unexpected rearrangement in the overcrowded polycyclic aromatic ene series
European Journal of Organic Chemistry, 2011Co-Authors: Naela Assadi, Sergey Pogodin, Israel AgranatAbstract:An attempted synthesis of the angularly annelated 9-(11'-benzo[a]fluoren-11'-ylidene)-9H-fluorene (3) through a Peterson Olefination reaction between (9H-fluoren-9-yl)trimethylsilyl anion (5a) and 11H-benzo[a]fluoren-11-one (6) led to the linearly annelated 9-(11'-benzo[b]fluoren-11'-ylidene)-9H-fluorene (4), due to an unexpected rearrangement. The proposed mechanism of the rearrangement is illustrated. The core of the mechanism is an intramolecular Haller-Bauer cleavage of the naphthyl C 11a' -C 11' bond in the β-oxysilane anion 11 (formed from 5a and 6) to give the 1-naphthyl anion (E)-12, followed by E/Z isomerization to (Z)-12 and by proton migration to give the 3-naphthyl anion (Z)-14. The intramolecular nucleophilic addition of the naphthyl anion at C-3' of (Z)-14 to the carbonyl carbon gives the β-oxysilane anion 15, a benzo[b]fluorenylidene derivative. The mechanism is supported by the results of DFT calculations. The synthesis of 3 was achieved by application of Barton's double extrusion diazo-thione coupling method.
Brent V Tyson - One of the best experts on this subject based on the ideXlab platform.
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scope and limitations of the Peterson Olefination reaction as a route to vinylidene phosphanes
European Journal of Organic Chemistry, 2004Co-Authors: Keith Izod, William Mcfarlane, Brent V TysonAbstract:The Peterson Olefination reaction has been investigated as a route to novel P-substituted alkenes. The reaction between [(nPr2P)2(Me3Si)C]Li and paraformaldehyde cleanly gives the symmetrical vinylidene phosphane (nPr2P)2C=CH2 (4) in good to excellent yields. In contrast, reactions between [(R2P)(Me3Si)2C]Li (R = Me, nPr) and paraformaldehyde yield complex mixtures of products which do not contain the expected vinylidene species. However, the unsymmetrical vinylidene phosphanes [nPr2P(BH3)](Me3Si)C=CH2 (6), (Ph2P)(iPr2P)C=CH2 (7), [nPr2P(S)](Me3Si)C=CH2 (10), [Ph2P(S)][iPr2P(S)]C=CH2 (11) and [Ph2P(S)][Me2P(S)]C=CH2 (12) are readily accessible by the Peterson Olefination reaction {compound 7 is obtained by deprotection of the corresponding borane adduct [Ph2P(BH3)][iPr2P(BH3)]C=CH2 with pyrrolidine}. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Naela Assadi - One of the best experts on this subject based on the ideXlab platform.
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Peterson Olefination unexpected rearrangement in the overcrowded polycyclic aromatic ene series
European Journal of Organic Chemistry, 2011Co-Authors: Naela Assadi, Sergey Pogodin, Israel AgranatAbstract:An attempted synthesis of the angularly annelated 9-(11'-benzo[a]fluoren-11'-ylidene)-9H-fluorene (3) through a Peterson Olefination reaction between (9H-fluoren-9-yl)trimethylsilyl anion (5a) and 11H-benzo[a]fluoren-11-one (6) led to the linearly annelated 9-(11'-benzo[b]fluoren-11'-ylidene)-9H-fluorene (4), due to an unexpected rearrangement. The proposed mechanism of the rearrangement is illustrated. The core of the mechanism is an intramolecular Haller-Bauer cleavage of the naphthyl C 11a' -C 11' bond in the β-oxysilane anion 11 (formed from 5a and 6) to give the 1-naphthyl anion (E)-12, followed by E/Z isomerization to (Z)-12 and by proton migration to give the 3-naphthyl anion (Z)-14. The intramolecular nucleophilic addition of the naphthyl anion at C-3' of (Z)-14 to the carbonyl carbon gives the β-oxysilane anion 15, a benzo[b]fluorenylidene derivative. The mechanism is supported by the results of DFT calculations. The synthesis of 3 was achieved by application of Barton's double extrusion diazo-thione coupling method.
Piotr Majewski - One of the best experts on this subject based on the ideXlab platform.
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mechanism of formation of aromatic vinylphosphonium salts via the Peterson Olefination
ChemInform, 2013Co-Authors: Ewa Lukaszewicz, Anna Kupinska, Piotr MajewskiAbstract:Para substituents in aromatic aldehydes determine the E/Z-selectivity in the Peterson Olefination due to their electron-donating or -withdrawing character.
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mechanism of formation of aromatic vinylphosphonium salts via the Peterson Olefination
Heteroatom Chemistry, 2013Co-Authors: Ewa łukaszewicz, Anna Kupinska, Piotr MajewskiAbstract:The mechanism of the reaction of tributyl[(trimethylsilyl)methylene]phosphorane with benzaldehyde and its p-substituted analogues has been examined. It has been found that the electronic nature of the p-substituents in aromatic aldehydes strongly influences the stereochemical and kinetic outcome of the Peterson Olefination whereas temperature substantially affects their Hammett correlation. This indicates that the Peterson Olefination is a multistep reaction involving the formation of at least an oxyanion/betaine and a carbanion as intermediates. In turn, moderate Z-selectivity might be the result of “steric approach intermediate control”; however, E-selectivity seems to result from the silicon–oxygen interaction and interactions of steric substituents in competing erythro- and threo-betaines.