Publications by authors named "Isa Kallweit"

3 Publications

  • Page 1 of 1

Brønsted-Acid-Catalyzed (3+2)-Cycloannulation of In-Situ-Generated 3-Methide-3-pyrroles: Asymmetric Synthesis of Cyclopenta[]pyrroles.

Org Lett 2020 Nov 11;22(22):9065-9070. Epub 2020 Nov 11.

Institut für Organische Chemie, Universität Leipzig, Johannisallee 29, 04103 Leipzig, Germany.

An organocatalytic, highly enantioselective addition of cyclic enamides to in-situ-generated 3-methide-3-pyrroles with subsequent cyclization and elimination has been developed. This protocol represents a novel and straightforward route toward polycyclic cyclopenta[]pyrroles with high yields and excellent enantioselectivity. Central to the success is the formation of a chiral, hydrogen-bonded 3-methide-3-pyrrole upon phosphoric-acid-catalyzed dehydration of the starting 1-pyrrol-3-yl carbinol that reacts with the enamide in a stepwise cycloannulation process.
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http://dx.doi.org/10.1021/acs.orglett.0c03452DOI Listing
November 2020

Brønsted Acid Catalyzed [6 + 2]-Cycloaddition of 2-Vinylindoles with in Situ Generated 2-Methide-2 H-pyrroles: Direct, Catalytic, and Enantioselective Synthesis of 2,3-Dihydro-1 H-pyrrolizines.

Org Lett 2019 01 8;21(2):519-523. Epub 2019 Jan 8.

Institut für Organische Chemie , Universität Leipzig , Johannisallee 29 , 04103 Leipzig , Germany.

We describe herein an organocatalytic, diastereo- and enantioselective [6 + 2]-cycloaddition toward the synthesis of densely substituted 2,3-dihydro-1 H-pyrrolizines bearing three contiguous stereogenic centers which are obtained with good yields, as single diastereomers, and with excellent enantioselectivity. A crucial feature of this one-step process leading to a prominent structural motif in many biologically active natural products is a BINOL-derived phosphoric acid catalyzed reaction of 1 H-pyrrole-2-yl carbinols with 2-vinylindoles via the corresponding hydrogen-bonded chiral 2-methide-2 H-pyrroles.
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http://dx.doi.org/10.1021/acs.orglett.8b03833DOI Listing
January 2019

A Highly Stereoselective Synthesis of Tetrahydrofurans.

Angew Chem Int Ed Engl 2017 06 9;56(24):6758-6761. Epub 2017 May 9.

Institut für Organische Chemie, Universität Leipzig, Johannisallee 29, 04103, Leipzig, Germany.

The development of a direct and highly stereoselective synthesis of 2,3,5-substituted tetrahydrofurans has been accomplished through a combination of batch- and microchip-MS-experiments. This sequential transformation comprises a Lewis acid-mediated reaction of bis(silyl) dienediolate 1 and a broad range of aldehydes, furnishing products with three new σ-bonds and three stereogenic centers in a one-pot process with typically good yields and excellent stereoselectivity. Key steps which have been elucidated primarily with microchip-MS-experiments include a vinylogous aldol reaction and a Prins-type cyclization. Furthermore, a titanium BINOL complex is a powerful chiral catalyst for this process. The products were further converted into bi- and tricylic products by carbonyl-ene reactions, proceeding with excellent yields and diastereoselectivity.
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http://dx.doi.org/10.1002/anie.201700774DOI Listing
June 2017