title: Highly Functionalized Cyclopentane Derivatives by Tandem Michael Addition/Radical Cyclization/Oxygenation Reactions.
abstract: Densely functionalized cyclopentane derivatives with up to four consecutive stereocenters are assembled by a tandem Michael addition/single-electron transfer oxidation/radical cyclization/oxygenation strategy mediated by ferrocenium hexafluorophosphate, a recyclable, less toxic single-electron transfer oxidant. Ester enolates were coupled with α-benzylidene and α-alkylidene β-dicarbonyl compounds with switchable diastereoselectivity. This pivotal steering element subsequently controls the diastereoselectivity of the radical cyclization step. The substitution pattern of the radical cyclization acceptor enables a switch of the cyclization mode from a 5-exo pattern for terminally substituted olefin units to a 6-endo mode for internally substituted acceptors. The oxidative anionic/radical strategy also allows efficient termination by oxygenation with the free radical 2,2,6,6-tetramethyl-1-piperidinoxyl, and two C-C bonds and one C-O bond are thus formed in the sequence. A stereochemical model is proposed that accounts for all of the experimental results and allows the prediction of the stereochemical outcome. Further transformations of the synthesized cyclopentanes are reported.
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo náměstí 2, 16610 Prague (Czech Republic).
authors.forename: Martin
authors.initials: M
authors.lastname: Holan
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo náměstí 2, 16610 Prague (Czech Republic).
authors.forename: Radek
authors.initials: R
authors.lastname: Pohl
authors.affiliation: Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030/8, 12843 Prague (Czech Republic).
authors.forename: Ivana
authors.initials: I
authors.lastname: Císařová
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo náměstí 2, 16610 Prague (Czech Republic).
authors.forename: Blanka
authors.initials: B
authors.lastname: Klepetářová
authors.affiliation: Institut für Anorganische und Allgemeine Chemie, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig (Germany).
authors.forename: Peter G
authors.initials: PG
authors.lastname: Jones
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo náměstí 2, 16610 Prague (Czech Republic). jahn@uochb.cas.cz.
authors.forename: Ullrich
authors.initials: U
authors.lastname: Jahn
keywords: Michael addition; cyclization; domino reactions; electron transfer; radical reactions