Universität zu Köln

Ratsch, Friederike, Schlundt, Waldemar, Albat, Dominik, Zimmer, Anne, Neudoerfl, Joerg-Martin, Netscher, Thomas and Schmalz, Hans-Guenther ORCID: 0000-0003-0489-1827 (2019). Total Synthesis of alpha-Tocopherol through Enantioselective Iridium-Catalyzed Fragmentation of a Spiro-Cyclobutanol Intermediate. Chem.-Eur. J., 25 (19). S. 4941 - 4946. WEINHEIM: WILEY-V C H VERLAG GMBH. ISSN 1521-3765

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Abstract

A conceptionally new strategy for the asymmetric (2R-selective) synthesis of alpha-tocopherol (vitamin E) was developed. In the stereocontrolled key step, a prochiral spiro[chromane-2,3 '-cyclobutanol] unit is effectively desymmetrized under C-C bond activation in an unprecedented iridium-catalyzed transformation using (S)-DTBM-SegPhos as a chiral ligand (e.r. 97:3). To complete the synthesis, the side chain was attached through Ru-catalyzed cross-metathesis employing an alkene derived from (R,R)-hexahydrofarnesol. To suppress epimerization during the final hydrogenation, PtO2 had to be used as a catalyst instead of Pd/C. In an alternative approach (employing a propargyl-substituted spiro-cyclobutanol), the side chain was constructed prior to the Ir-catalyzed ring fragmentation (>99:1 d.r.) through enyne cross-metathesis (using an alkene derived from (R)-dihydrocitronellal) followed by Cr-catalyzed 1,4-hydrogenation and (diastereoselective) Pfaltz hydrogenation of the resulting triple-substituted olefin. The work demonstrates the potential of iridium catalysis for enantioselective C-C bond activation.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Ratsch, Friederike UNSPECIFIED UNSPECIFIED UNSPECIFIED Schlundt, Waldemar UNSPECIFIED UNSPECIFIED UNSPECIFIED Albat, Dominik UNSPECIFIED UNSPECIFIED UNSPECIFIED Zimmer, Anne UNSPECIFIED UNSPECIFIED UNSPECIFIED Neudoerfl, Joerg-Martin UNSPECIFIED UNSPECIFIED UNSPECIFIED Netscher, Thomas UNSPECIFIED UNSPECIFIED UNSPECIFIED Schmalz, Hans-Guenther UNSPECIFIED orcid.org/0000-0003-0489-1827 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-152219
DOI:	10.1002/chem.201900564
Journal or Publication Title:	Chem.-Eur. J.
Volume:	25
Number:	19
Page Range:	S. 4941 - 4946
Date:	2019
Publisher:	WILEY-V C H VERLAG GMBH
Place of Publication:	WEINHEIM
ISSN:	1521-3765
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Chemistry > Institute of Organic Chemistry
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language C BOND-CLEAVAGE; VITAMIN-E; GRIGNARD-REAGENTS; CROSS-METATHESIS; ASYMMETRIC HYDROGENATION; ENYNE METATHESIS; CONSTRUCTION; HYDROCARBONS; ALCOHOLS; OLEFINS Multiple languages Chemistry, Multidisciplinary Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/15221