- Highly Enantioselective Hydrogenation of α-Arylmethylene Cycloalkanones Catalyzed by Iridium Complexes of Chiral Spiro Aminophosphine Ligands
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The highly efficient asymmetric hydrogenation of α-arylmethylene cycloalkanones catalyzed by Ir-complexes of chiral spiro aminophosphine ligands was developed, providing chiral exo-cyclic allylic alcohols at high yields with excellent enantioselectivities (up to 97% ee) and high turnover numbers (S/C up to 10,000). This new reaction provided an efficient method for the synthesis of the key intermediate of the active form of the anti-inflammatory loxoprofen.
- Xie, Jian-Bo,Xie, Jian-Hua,Liu, Xiao-Yan,Kong, Wei-Ling,Li, Shen,Zhou, Qi-Lin
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supporting information; experimental part
p. 4538 - 4539
(2010/06/17)
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- Perturbations by phenyl on the 1,5-hydrogen shift in 1,3(Z)-pentadiene. Another chameleonic transition region?
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The acyclic 1,5-dienyl hydrogen shift is accelerated by radical-stabilizing phenyl substituents without regard to the type of position occupied in the 1,3(Z)-pentadiene system. 1-Phenyl-5-p-tolyl-1,3(Z)-pentadiene has a corrected energy of activation 5.8 kcal mol-1 lower than that of the parent, while the 2-and 3-phenyl analogues, examined in cyclic systems specifically designed to obviate the otherwise general need for a thermochemical correction to the immediately precursory s-cis conformation, reveal stabilizing effects of 3.6 and 3.4 kcal mol-1, respectively. These relatively small effects are consistent with a chameleonic conceptual scheme for the transition region.
- Doering, William Von E.,Keliher, Edmund J.,Zhao, Xin
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p. 14206 - 14216
(2007/10/03)
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- The reaction of enaminones with grignard reagents: Synthesis of α,β- unsaturated ketones
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Enaminones in toluene react with Grignard reagents in tetrahydrofuran at 0-25 °C, to give selectively and with high yields the corresponding α,β- unsaturated ketones.
- Fontenas,Ait-Haddou,Bejan,Balavoine
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p. 1743 - 1753
(2007/10/03)
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- α-ALKYLATION AND α-ALKYLIDENATION OF CARBONYL COMPOUNDS BY O-SILYLATED ENOLATE PHENYLTHIOALKYLATION
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For many reactions next to a carbonyl group, the use of O-silylated enolate chemistry offers improvements in yield and selectivity over the corresponding reactions of Group I metal enolates.In the case of α-alkylation of carbonyl compounds, Lewis acid (TiCl4 or ZnBr2) promoted phenylthioalkylation of O-silylated enolates 3 by α-chlorosulphides 4 (R3=H, Me, Prn, Pri, Bui, and Me3Si), followed by reductive sulphur removal by Raney nickel, 5->6, is found to be a reliable method for this synthetically important C-C bond forming step.An alternative sulphur elimination pathway via the sulphoxide, 5->7, allows the regio- and stereocontrolled α-alkylidenation of carbonyl compounds.The phenylthioalkylation reaction is applicable to ketones, aldehydes, esters, and lactones.
- Paterson, Ian
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p. 4207 - 4220
(2007/10/02)
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- A Michael Addition-Induced Favorskii Rearrangement
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Reaction of 6-chloro-2-vinylidenecyclohexanone with sodium methoxide gave methyl 2-vinylidene-1-cyclopentanecarboxylate and methyl trans-2-(1-methoxy-alkyl)-1-cyclopentanecarboxylate along with 6-methoxy-2-vinylidenecyclohexanone via a Michael addition-induced Favorskii rearrangement.
- Tsuboi, Sadao,Nagae, Hiroyuki,Yamato, Hirofumi,Takeda, Akira
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p. 836 - 838
(2007/10/02)
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- Cross-Condensation Reactions of Cycloalkanones with Aldehydes and Primary Alcohols under the Influence of Zirconocene Complexes.
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Under the influence of zirconocene complex,Cp2ZrH2 (1) or Cp2Zr(O-i-Pr)2 (9),cycloalkanones 2 condensed directly with aliphatic aldehydes 3 or primary alcohols 7 to form 2-alkylidenecycloalkanones 4 or 2-alkyl-2-cycloalken-1-ones 8,respectively,in fair to substantial yields.The selectivity of the cross-condensations was slighty improved by using 1 in combination with a metal salt such as NiCl2.Dihydrojasmone (13) was synthesized in 35percent yield by one-step reaction from the commercially available 3-methylpentanone (2e) with pentanol (7b) in the presence of 1 and NiCl2.
- Nakano Tatsuya,Irifune Shinji,Umano Shigetoshi,Inada Akihiro,Ishii Yasutaka,Ogawa Masaya
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p. 2239 - 2244
(2007/10/02)
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- Synthesis of β,γ-Unsaturated Ketones and γ-Hydroxy Carbonyl Compounds from Methyl 2-Siloxycyclopropanecarboxylates
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Several methyl 2-siloxycyclopropanecarboxylates 5 are smoothly transformed into isomerically pure β,γ-unsaturated carbonyl compounds 10 by reduction with LiAlH4 or by addition of methyllithium followed by ring cleavage with acid.The method fails with bicyclic and phenyl-substituted starting materials.The intermediates obtained by reduction can also be treated with base affording γ-hydroxy carbonyl compounds 12 regioselectively.
- Bretsch, Wolfgang,Reissig, Hans-Ulrich
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p. 175 - 178
(2007/10/02)
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- On Conformational Sensitivity in the Ultraviolet Spectra of Cyclopropyl Ketones and Olefins
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Selected cyclopropyl ketones and olefins have been prepared to approximate the three principal conformers (s-trans, s-cis, and gauche) of vinylcyclopropane and cyclopropanecarboxaldehyde.The model systems are as follows: for the s-cis form, 4-oxo- (VI) an
- Van-Catledge, Frederic A.,Boerth, Donald W.,Kao, James
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p. 4096 - 4106
(2007/10/02)
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