- Asymmetric Nazarov Cyclizations of Unactivated Dienones by Hydrogen-Bond-Donor/Lewis Acid Co–Catalyzed, Enantioselective Proton-Transfer
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We report an enantioselective Nazarov cyclization catalyzed by chiral hydrogen-bond-donors in concert with silyl Lewis acids. The developed transformation provides access to tri-substituted cyclopentenones in high levels of enantioselectivity (up to 95% e.e.) from a variety of simple unactivated dienones. Kinetic and mechanistic studies are consistent with a reversible 4π-electrocyclization C?C bond-forming step followed by rate- and enantio-determining proton-transfer as the mode of catalysis. (Figure presented.).
- Metternich, Jan B.,Reiterer, Martin,Jacobsen, Eric N.
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supporting information
p. 4092 - 4097
(2020/09/01)
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- Dianionic Phase-Transfer Catalyst for Asymmetric Fluoro-cyclization
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Inspired by the dicationic nature of the electrophilic fluorinating reagent, Selectfluor (1), we rationally designed a series of dicarboxylic acid precatalysts (2), which, when deprotonated, act as anionic phase-transfer catalysts for asymmetric fluorination of alkenes. Among them, 2a having the shortest linker moiety efficiently catalyzed unprecedented 6-endo-fluoro-cyclization of various allylic amides, affording fluorinated dihydrooxazine compounds with high enantioselectivity (up to 99% ee). In addition to cyclic substrates, acyclic trisubstituted alkenes underwent the reaction with good diastereoselectivity, whereas low diastereoselectivity was observed for linear disubstituted alkenes. Results suggest that the reaction proceeds via a fluoro-carbocation intermediate.
- Egami, Hiromichi,Niwa, Tomoki,Sato, Hitomi,Hotta, Ryo,Rouno, Daiki,Kawato, Yuji,Hamashima, Yoshitaka
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supporting information
p. 2785 - 2788
(2018/03/08)
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- β-disubstituted allylic chlorides: Substrates for the Cu-catalyzed asymmetric SN2′ reaction
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Scope broadened: A previously developed asymmetric Cu-catalyzed allylic substitution can be applied to more substituted allylic patterns. Two classes of β-disubstituted substrates, cinnamyl derivatives and aliphatic endocyclic allylic chlorides, afford excellent regio- and enantioselectivities (see schemes; L* = phosphoramidite ligand). (Chemical Equation Presented).
- Falciola, Caroline A.,Tissot-Croset, Karine,Alexakis, Alexandre
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p. 5995 - 5998
(2007/10/03)
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