- TADDOL-TiCl2 catalyzed Diels-Alder reactions: Unexpected influence of the substituents in the 2-position of the dioxolane ring on the stereoselectivity
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Several α,α,α',α'-tetra(3,5-dimethylphenyl)-1,3-dioxolane-4,5-dimethanols have been synthesized, and their TiCl2 derivatives used as catalysts in the reaction of cyclopentadiene with (E)-2-butenoyl-1,3-oxazolidin-2-one. The substituents in the 2-position of the dioxolane ring exert a decisive influence on the extent and direction of the asymmetric induction and, consequently any possible enantiomer of the cycloadducts can be preferentially obtained by changing these substituents. Molecular mechanics calculations of the structures and relative energies of the possible dienophile-catalyst complexes offer a tentative explanation for the results described.
- Altava, Belen,Burguete, Ma. Isabel,Fraile, Jose M.,Garcia, Jose I.,Luis, Santiago V.,Mayoral, Jose A.,Royo, Ana J.,Vicent, Maria J.
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- P-Anisaldehyde-Photosensitized Sulfonylcyanation of Chiral Cyclobutenes: Enantioselective Access to Cyclic and Acyclic Systems Bearing All-Carbon Quaternary Stereocenters
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The photosensitized p-Anisaldehyde-mediated addition of sulfonylcyanides onto the I -system of cyclobutenes is shown to afford highly functionalized cyclobutanes in high yields and diastereocontrol. The homochiral cyclobutene precursors are accessible on multigram scale in two steps through an asymmetric [2 + 2] cycloaddition/vinyl thioether reduction sequence. The enantiopure cyclobutylnitriles can be elaborated further through SmI2-mediated ring opening or converted into new enantiopure cyclobutenes through base-mediated sulfone elimination.
- Pirenne, Vincent,Traboulsi, Iman,Rouvière, Lisa,Lusseau, Jonathan,Massip, Stéphane,Bassani, Dario M.,Robert, Frédéric,Landais, Yannick
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- Asymmetric Diels-Alder Reaction Catalyzed by a Chiral Titanium Reagent
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A highly enantioselective Diels-Alder reaction has been developed by employing a chiral titanium reagent generated in situ from dichlorodiisopropoxytitanium and the chiral diol 1d, which is easily derived from tartaric acid.With a catalytic amount of the
- Narasaka, Koichi,Iwasawa, Nobuharu,Inoue, Masayuki,Yamada, Tohru,Nakashima, Masako,Sugimori, Jun
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p. 5340 - 5345
(2007/10/02)
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- Asymmetric Hydrocyanation of Aldehydes Using Chiral Titanium Reagents
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Two highly enantioselective methods for hydrocyanation of aldehydes were developed by using chiral alkoxytitanium reagents.Treatment of benzaldehyde with cyanotrimethylsilane in the presence of a chiral alkoxytitanium affords mandelonitrile in good chemic
- Minamikawa, Hiroyuki,Hayakawa, Satoshi,Yamada, Tohru,Iwasawa, Nobuharu,Narasaka, Koichi
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p. 4379 - 4384
(2007/10/02)
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- ASYMMETRIC DIELS-ALDER REACTION PROMOTED BY A CHIRAL TITANIUM REAGENT
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The asymmetric Diels-Alder reaction between prochiral dienes and dienophiles prepared from α,β-unsaturated acids and 1,3-oxazolidin-2-one proceeds by the use of a chiral alkoxy titanium(IV) to give the corresponding cycloadducts in high enantioselectivity
- Narasaka, Koichi,Inoue, Masayuki,Okada, Naoko
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p. 1109 - 1112
(2007/10/02)
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