title: Radical 4-exo cyclizations via template catalysis.
abstract: The mechanism of catalytic 4-exo cyclizations without gem-dialkyl substitution was investigated by a comparison of cyclic voltammetry, EPR, and computational studies with previously published synthetic results. The most active catalyst is a super-unsaturated 13-electron titanocene(III) complex that is formed by supramolecular activation through hydrogen bonding. The template catalyst binds radicals via a two-point binding that is mandatory for the success of the 4-exo cyclization. The computational investigations revealed that formation of the observed trans-cyclobutane product is not possible from the most stable substrate radical. Instead, the most stable product is formed with the lowest energy of activation from a disfavored substrate in a Curtin-Hammett related scenario.
authors.affiliation: Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Gerhard Domagk Str. 1, 53121 Bonn, Germany. andreas.gansaeuer@uni-bonn.de
authors.forename: Andreas
authors.initials: A
authors.lastname: Gansäuer
authors.forename: Karsten
authors.initials: K
authors.lastname: Knebel
authors.forename: Christian
authors.initials: C
authors.lastname: Kube
authors.forename: Maurice
authors.initials: M
authors.lastname: van Gastel
authors.forename: Asli
authors.initials: A
authors.lastname: Cangönül
authors.forename: Kim
authors.initials: K
authors.lastname: Daasbjerg
authors.forename: Tim
authors.initials: T
authors.lastname: Hangele
authors.forename: Michael
authors.initials: M
authors.lastname: Hülsen
authors.forename: Michael
authors.initials: M
authors.lastname: Dolg
authors.forename: Joachim
authors.initials: J
authors.lastname: Friedrich
mesh_terms: D000473:Alkanes / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D006860:Hydrogen Bonding; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000473:Alkanes; D009942:Organometallic Compounds; C406884:titanocene