Asymmetric Hydrogenation of 3-Substituted Pyridinium Salts

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 Et3N, a Rh‐JosiPhos catalyst reduced a range of pyridinium salts with ee...

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Veröffentlicht in:	Chemistry : a European journal Jg. 22; H. 28; S. 9528 - 9532
Hauptverfasser:	Renom-Carrasco, Marc, Gajewski, Piotr, Pignataro, Luca, de Vries, Johannes G., Piarulli, Umberto, Gennari, Cesare, Lefort, Laurent
Format:	Journal Article
Sprache:	Englisch
Veröffentlicht:	WEINHEIM Blackwell Publishing Ltd 04.07.2016 Wiley Wiley Subscription Services, Inc
Schlagworte:	asymmetric catalysis Asymmetry Chemistry Chemistry, Multidisciplinary Equivalence homogeneous catalysis Hydrogenation Isotopic labeling Labyrinth Pathways Physical Sciences Piperidine Pyridines reaction mechanisms Salts Science & Technology SCOPE MONODENTATE PHOSPHORAMIDITE LIGANDS reaction mechanisms QUINOLINES asymmetric catalysis DEHYDROAMINO ACID-DERIVATIVES hydrogenation MULTIPLE STEREOGENIC CENTERS IRIDIUM-CATALYZED HYDROGENATION HIGHLY ENANTIOSELECTIVE HYDROGENATION pyridines homogeneous catalysis REDUCTION PIPERIDINES ISOQUINOLINIUM SALTS
ISSN:	0947-6539, 1521-3765, 1521-3765
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Zusammenfassung:	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 Et3N, 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. Ariadne′s thread: The asymmetric hydrogenation of 3‐substitued pyridines has been achieved with up to 90 % ee. The use of an equivalent amount of an organic base turned out to be crucial to avoid unwanted pathways leading to non‐enantioselective reduction. An in‐depth investigation of the mechanism revealed a labyrinth of hydrogenation pathways with many dead ends (see figure).
Bibliographie:	ArticleID:CHEM201601501 European Commission ark:/67375/WNG-7C78WR4T-T ITN-EID "REDUCTO" - No. PITN-GA-2012-316371 istex:5906FA8FEBE3E02BBD230789F973CC92D9AAC2CF ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 14 content type line 23
ISSN:	0947-6539 1521-3765 1521-3765
DOI:	10.1002/chem.201601501