title: Asymmetric Hydrogenation of 3-Substituted Pyridinium Salts.
abstract: The use of an equivalent amount of an organic base leads to high enantiomeric excess in the asymmetric hydrogenation of N-benzylated 3-substituted pyridinium salts into the corresponding piperidines. Indeed, in the presence of Et3 N, a Rh-JosiPhos catalyst reduced a range of pyridinium salts with ee values up to 90 %. The role of the base was elucidated with a mechanistic study involving the isolation of the various reaction intermediates and isotopic labeling experiments. Additionally, this study provided some evidence for an enantiodetermining step involving a dihydropyridine intermediate.
authors.affiliation: DSM Ahead R&D B.V.-Innovative Synthesis, P. O. Box 18, 6160 MD, Geleen, The Netherlands.|Dipartimento di Chimica, Università degli Studi di Milano, via C. Golgi 19, 20133, Milan, Italy.
authors.forename: Marc
authors.initials: M
authors.lastname: Renom-Carrasco
authors.affiliation: DSM Ahead R&D B.V.-Innovative Synthesis, P. O. Box 18, 6160 MD, Geleen, The Netherlands.|Dipartimento di Chimica, Università degli Studi di Milano, via C. Golgi 19, 20133, Milan, Italy.
authors.forename: Piotr
authors.initials: P
authors.lastname: Gajewski
authors.affiliation: Dipartimento di Chimica, Università degli Studi di Milano, via C. Golgi 19, 20133, Milan, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Pignataro
authors.affiliation: Leibniz-Institut für Katalyse e.V. an der, Universität Rostock, Albert-Einstein-Str. 29a, 18059, Rostock, Germany.
authors.forename: Johannes G
authors.identifier: http://orcid.org/0000-0001-5245-7748
authors.initials: JG
authors.lastname: de Vries
authors.affiliation: Dipartimento di Scienza e Alta Tecnologia, Università degli Studi dell'Insubria, via Valleggio 11, 22100, Como, Italy.
authors.forename: Umberto
authors.initials: U
authors.lastname: Piarulli
authors.affiliation: Dipartimento di Chimica, Università degli Studi di Milano, via C. Golgi 19, 20133, Milan, Italy.
authors.forename: Cesare
authors.initials: C
authors.lastname: Gennari
authors.affiliation: DSM Ahead R&D B.V.-Innovative Synthesis, P. O. Box 18, 6160 MD, Geleen, The Netherlands. laurent.lefort@dsm.com.
authors.forename: Laurent
authors.identifier: http://orcid.org/0000-0003-2973-6540
authors.initials: L
authors.lastname: Lefort
keywords: asymmetric catalysis; homogeneous catalysis; hydrogenation; pyridines; reaction mechanisms