Publications by authors named "Christoph Schotes"

8 Publications

  • Page 1 of 1

Total synthesis of (18S)- and (18R)-homolargazole by rhodium-catalyzed hydrocarboxylation.

Chemistry 2014 Feb 29;20(8):2164-8. Epub 2014 Jan 29.

Institut für Organische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104 Freiburg i. Bg. (Germany), Fax: (+49) 761-203-8715.

Homolargazole derivatives, in which the macrocycle of natural largazole is extended by one methylene group, were prepared by the recently developed rhodium-catalyzed hydrocarboxylation reaction onto allenes. This strategy gives access to both the (18S)- and (18R)-stereoisomers in high stereoselectivity under ligand control.
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http://dx.doi.org/10.1002/chem.201303300DOI Listing
February 2014

Asymmetric hydrogenation of ketones with H2 and ruthenium catalysts containing chiral tetradentate S2N2 ligands.

Angew Chem Int Ed Engl 2013 Sep 12;52(39):10352-5. Epub 2013 Aug 12.

Corporate R&D Division, Firmenich SA route des Jeunes 1, P.O. Box 239, 1211 Genève 8 (Switzerland).

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http://dx.doi.org/10.1002/anie.201304844DOI Listing
September 2013

Asymmetric Diels-Alder and Ficini reactions with alkylidene β-ketoesters catalyzed by chiral ruthenium PNNP complexes: mechanistic insight.

J Am Chem Soc 2012 Jan 6;134(2):1331-43. Epub 2012 Jan 6.

Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland.

Hydride abstraction from the β-position of the enolato ligand of the previously reported complex [Ru(3a-H)(PNNP)]PF(6) (5a; 3a-H is the enolate of 2-tert-butoxycarbonylcyclopentanone) with (Ph(3)C)PF(6) gives the dicationic complex [Ru(6a)(PNNP)](2+) (7a) as a single diastereoisomer, which contains the unsaturated β-ketoester 2-tert-butoxycarbonyl-2-cyclopenten-1-one (6a) as a chelating ligand. The methyl analogue 2-methoxycarbonylcyclopentanone (3b) gives [Ru(3b-H)(PNNP)]PF(6) as a mixture of noninterconverting diastereoisomers (ester group of 3b trans to P, 5b; or to N, 5c), which were separated by column chromatography. Hydride abstraction from 5b (or 5c) yields diastereomerically pure [Ru(6b)(PNNP)](2+) (7b or 7c). Complexes 7b and 7c do not interconvert at room temperature in CD(2)Cl(2) and form opposite enantiomers of the Diels-Alder adduct upon reaction with Dane's diene (1 equiv). X-ray studies of 7a, 5b, and 5c give insight into the origin of enantioselection and the sense of asymmetric induction in the previously reported asymmetric Diels-Alder and Ficini cycloaddition reactions with 2,3-disubstituted butadienes and ynamides, respectively. Stoichiometric reactions (substrate coordination, cycloaddition, and product displacement) between [Ru(OEt(2))(2)(PNNP)](2+) (2), 6b (or 6a), and Dane's diene (15, to give estrone derivatives) or N-benzyl-N-(cyclohexylethynyl)-4-methylbenzenesulfonamide (17, to give cyclobutenamides) suggest that product displacement from the catalyst is turnover limiting.
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http://dx.doi.org/10.1021/ja210372uDOI Listing
January 2012

Enantioselective Diels-Alder reactions of unsaturated beta-ketoesters catalyzed by chiral ruthenium PNNP complexes.

Chimia (Aarau) 2011 ;65(4):231-4

Laboratory of Inorganic Chemistry, ETH Zürich, CH-8093 Zürich.

We report here dicationic ruthenium PNNP complexes that promote the enantioselective Diels-Alder reaction of alpha-methylene beta-ketoesters with various dienes. Complex [Ru(OEt2)2(PNNP)](PF6)2, formed in situ from [RuCl2,(PNNP)] and (Et3O)PF6 (2 equiv.), catalyzes the Diels-Alder reaction of such unsaturated beta-ketoesters to give novel alkoxycarbonyltetrahydro-1-indanone derivatives (nine examples) with up to 93% ee. The crystal structure of the substrate-catalyst adduct shows that the lower face of the substrate is shielded by a phenyl ring of the PNNP ligand, which accounts for the high enantioselectivity. The attack of the diene from the open re enantioface of the unsaturated beta-ketoester is consistent with the absolute configuration of the product. A useful application of this method is the reaction with Dane's diene to give estrone derivatives with up to 99% ee and an ester-exo:endo ratio of up to 145:1 (after recrystallization). Besides the enantioselective formation of all-carbon quaternary centers, this methodology is notable because unsaturated beta-ketoesters have been rarely used in Diels-Alder reactions. Furthermore, enantiomerically pure estrone derivatives are interesting in view of their potential applications, including the treatment of breast cancer.
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August 2011

Cu(I)- and Cu(II)-catalyzed cyclo- and Michael addition reactions of unsaturated β-ketoesters.

J Org Chem 2011 Jul 15;76(14):5862-6. Epub 2011 Jun 15.

Department of Chemistry and Applied Biosciences, ETH Zürich, Zürich, Switzerland.

The α-alkylidene β-ketoesters 2-carbethoxycyclopentenone (1a) and ethyl 2-benzoylacrylate (1b) react with 1,2-dimethylbutadiene (2) (Diels-Alder), N-benzyl-N-(cyclohexylethynyl)-4-methylbenzenesulfonamide (3) (Ficini reaction), ethynyl(phenyl)sulfane (4) ([2 + 2] cycloaddition), and 1,2,5-trimethyl-1H-pyrrole (5) (Michael addition) in the presence of copper(I) (6) or copper(II) triflate (7) (1-2 mol %) in dichloromethane. This convenient protocol converts 1a and 1b to the corresponding cycloaddition (8-10) or Michael addition (11) products in good yields after reaction times of 0.5-3 h without requiring purified solvents or inert gas atmosphere.
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http://dx.doi.org/10.1021/jo200776cDOI Listing
July 2011

Enantioselective Ficini reaction: ruthenium/PNNP-catalyzed [2+2] cycloaddition of ynamides with cyclic enones.

Angew Chem Int Ed Engl 2011 Mar 25;50(13):3072-4. Epub 2011 Feb 25.

Departement Chemie und Angewandte Biowissenschaften, ETH Zürich, Zürich, Switzerland.

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http://dx.doi.org/10.1002/anie.201007753DOI Listing
March 2011

Asymmetric Diels-Alder reactions of unsaturated beta-ketoesters catalyzed by chiral ruthenium PNNP complexes.

J Am Chem Soc 2010 Mar;132(11):3652-3

Department of Chemistry and Applied Biosciences, ETH Zurich, CH-8093 Zürich, Switzerland.

Cyclic alpha-unsaturated beta-ketoesters undergo cycloaddition with di- and trisubstituted butadienes to give tetrahydro-1-indanone derivatives with up to 93% ee in the presence of a ruthenium catalyst formed by activation of [RuCl(2)(PNNP)] with (Et(3)O)PF(6) (2 equiv) (PNNP = (1S,2S)-N,N'-bis[o-(diphenylphosphino)benzylidene]cyclohexane-1,2-diamine). The protocol has been used to prepare the estrone derivative (8R,13S,14S)-13-tert-butoxycarbonyl-3-methoxy-7,8,12,13,15,16-hexahydro-6H-cyclopenta[a]phenanthren-17(14H)-one as a single diastereoisomer with 85% yield and 99% ee after one crystallization step. Its absolute configuration, which has been determined by X-ray diffraction after reduction to the alcohol and esterification with camphanic chloride, is in agreement with the attack of the diene onto the open enantioface of the beta-keto ester (O-O) in the ruthenium complex [Ru(O-O)(PNNP)](2+), whose X-ray structure has been determined.
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http://dx.doi.org/10.1021/ja910039eDOI Listing
March 2010
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