title: Regioselective Synthesis of α-Fluorinated Cyclopentenones by Organocatalytic Difluorocyclopropanation and Fluorine-Directed and Fluorine-Activated Nazarov Cyclization.
abstract: Silyl dienol ethers, prepared from α,β-unsaturated ketones, underwent proton sponge-catalyzed difluorocyclopropanation with trimethylsilyl 2,2-difluoro-2-fluorosulfonylacetate in a regioselective manner, leading to 1,1-difluoro-2-siloxy-2-vinylcyclopropanes in good yields. The cyclopropanes thus obtained were in turn subjected to fluoride-ion-catalyzed ring opening to afford 1-fluorovinyl vinyl ketones (i.e., Nazarov precursors). Treatment of the precursors with Me3Si+B(OTf)4-regioselectively promoted the Nazarov cyclization, the rate and regioselectivity of which were drastically enhanced by the fluoro substituent, which thus facilitated efficient synthesis of biologically promising α-fluorocyclopentenone derivatives.
authors.affiliation: Division of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8571, Japan.
authors.forename: Kohei
authors.initials: K
authors.lastname: Fuchibe
authors.affiliation: Division of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8571, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Takayama
authors.affiliation: Department of Applied Chemistry, Faculty of Engineering, Kyushu Institute of Technology, Kitakyushu, Fukuoka, 804-8550, Japan.
authors.forename: Takaharu
authors.initials: T
authors.lastname: Yokoyama
authors.affiliation: Division of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8571, Japan.
authors.forename: Junji
authors.identifier: http://orcid.org/0000-0001-6498-326X
authors.initials: J
authors.lastname: Ichikawa
keywords: carbenes; cyclization; fluorine; organocatalysis; regioselectivity