- Copper-Catalyzed Enantioselective Conjugate Addition to α,β-Unsaturated Aldehydes with Various Organometallic Reagents
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β-Substituted aldehydes constitute a very important class of compounds found in nature. Synthesis of this motif can be envisioned by C-C bond formation on enals. For this purpose, we report herein the development of enantioselective copper-catalyzed conjugate addition of various organometallic reagents to α,β-unsaturated aldehydes with (R)-H8BINAP, (R)-TolBINAP, and (R)-SEGPHOS as chiral ligands. Three sets of conditions were successfully developed and several enals were used. Reactivity and regio- and enantioselectivities were strongly dependent on reaction conditions and substrates. Good to excellent regio- and enantioselectivities were obtained with zinc reagents R2Zn and aluminum reagents R3Al. However, the asymmetric conjugate addition of Grignard reagents afforded only moderate to good regio- and enantioselectivities.
- Goncalves-Contal, Sylvie,Gremaud, Ludovic,Palais, La?titia,Babel, Lucille,Alexakis, Alexandre
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p. 3301 - 3308
(2016/09/12)
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- Copper-catalyzed enantioselective 1,4-addition to α,β- unsaturated aldehydes
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Figure presented The first asymmetric Cu-catalyzed conjugate addition of dialkylzinc zinc reagents to a large scope of enals in presence of phosphoramidite, SimplePhos, or (R)-BINAP ligands with enantiomeric excesses up to 90% is reported. Moreover, ACA of Grignard reagents afforded moderate to good 1,4-regioselectivities with enantioselectivities up to 90%.
- Palais, Laetitia,Babel, Lucille,Quintard, Adrien,Belot, Sebastien,Alexakis, Alexandre
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supporting information; experimental part
p. 1988 - 1991
(2010/07/10)
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- Rhodium(I) complexes with N-heterocyclic carbenes bearing a 2,3,4,5-tetraphenylphenyl and its higher dendritic frameworks
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Novel rhodium(i) complexes with N-heterocyclic carbenes bearing a 2,3,4,5-tetraphenylphenyl and its higher dendritic frameworks were synthesized and the complexes were used as catalysts in rhodium-catalyzed hydrosilylation of α,β-unsaturated ketones to show high 1,4-adduct selectivity. The Royal Society of Chemistry.
- Sato, Hiromichi,Fujihara, Tetsuaki,Obora, Yasushi,Tokunaga, Makoto,Kiyosu, Junya,Tsuji, Yasushi
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p. 269 - 271
(2007/10/03)
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- Acid-catalyzed rearrangement of α-hydroxytrialkylsilanes
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Cationic rearrangement of several α-hydroxysilanes is described. Treatment of both (1R,1′R,2′S)-α-hydroxycyclopropylsilane syn-9 and (1S,1′R,2′S)-anti-9 under aqueous H2SO4 underwent rearrangement via a common α-silyl cation intermediate A to give a mixture of the ring-opened (R)-vinylsilane 13, the tandem [1,2]-CC bond migration product (1R,2S,1′R)-14, and its 1′S isomer 15. On the other hand, the acidic treatment of (R,E)-α-hydroxyalkenylsilane 8 or (R,Z)-8 was each accompanied with partial racemization to give an enantiomeric isomer of allylic alcohol 23 via a preferential syn-facial SN2′ reaction, respectively. Both α-hydroxyalkynylsilane 6 and α-hydroxyalkylsilane 12 were inert to the acidic conditions; however, treatment of (R)-α-mesyloxyalkynylsilane 26 under aqueous H2SO4 gave a mixture of the optically active rearranged allene 27, α,β-unsaturated ketone 28, and (S)-α-hydroxyalkynylsilane 6 with partial racemization. Comparisons of the reactivities of these α-hydroxysilanes under acidic conditions are also disclosed.
- Sakaguchi, Kazuhiko,Higashino, Masato,Ohfune, Yasufumi
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p. 6647 - 6658
(2007/10/03)
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