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Current research

Natural product synthesis

Total Synthesis of ent-Lepadin F and G by a Tandem Ene-Yne-Ene Ring Closing Metathesis

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The first total synthesis of the decahydroquinoline-alkaloids lepadin F and G is described. As key steps, the decahydroquinoline skeleton has been synthesized by utilizing a tandem ene-yne-ene ring closing metathesis of an acyclic precursor followed by a stereoselective hydrogenation of the resulting diene moiety. more to: Total Synthesis of ent-Lepadin F and G by a Tandem Ene-Yne-Ene Ring Closing Metathesis

Macrolide antibiotic (-)-A26771B

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The preparation of macrolides has received much attention due to their challenging structures and high biological activities. The key step of our synthesis was a macrolactonization strategy leading to a 16-membered ring. The thermal cycloreversion of dioxolenones followed by intramolecular ketene trapping constitutes a rather unexplored means for this conversion. Another key step was the introduction of the trans-diol moiety by Sharpless AD-methodology. more to: Macrolide antibiotic (-)-A26771B

(+)-Phomopsolide C

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Ring-size selective RCM and chemoselective CM as key bond forming reactions in the total synthesis of (+)-Phomopsolide C The phomopsolides belong to a series of related 6-substituted 5,6-dihydro-5-hydroxypyran-2-ones and are a new class of natural products possessing an effective antiboring/antifeeding activity against the elm bark beetle, which is responsibe for Dutch elm disease. more to: (+)-Phomopsolide C

(+)-trans-195A

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Decahydroquinoline trans-195A was first isolated as a trace compound from neotropical dendrobatid frogs of the genus Epipedobates bassleri. These amphibian alkaloids have proven to be non-competitive blockers of nicotinic receptor channels and are thus interesting agents for biomedical research. more to: (+)-trans-195A

Metathesis

Alternating Copolymerizations Using a Grubbs-Type Initiator Based on an Unsymmetrical, Chiral N-Heterocyclic Carbene

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Good for a ROMP: Initiators 1 and 2, which both contain an unsymmetric, chiral N-heterocyclic carbene (NHC) ligand, mediate the alternating copolymerization of norborn-2-ene with other cyclic olefins including cyclopentene and cyclooctene. The selectivity of the copolymerization is explained by the steric interaction of the growing polymer chain with the 1-phenylethyl substituent and the nitrogen atom of the NHC ligand. more to: Alternating Copolymerizations Using a Grubbs-Type Initiator Based on an Unsymmetrical, Chiral N-Heterocyclic Carbene

Catalyst development

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Kristallstruktur eines Rutheniumkomplexes mit NHC-Liganden.

New unsymmetrical NHC-ligands have been prepared from simple starting materials. They have also been complexed to ruthenium to give new metathesis initiators. The new complexes gave significantly different E/Z ratios in cross metathesis reactions and gave improved selectivity in diastereoselective ring-closing metathesis in comparison to the corresponding Grubbs II and Hoveyda-Grubbs complexes. more to: Catalyst development

Sequential Catalysis

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A common goal in the developement of new reactions is not only high catalyst efficiency, but also the use of a single catalyst for more than one chemical transformation in a single synthetic operation. Ultimately this could lead to the use of a single catalyst to mediate two or more reactions that are fundamentally different in nature, so-called sequential catalysis. more to: Sequential Catalysis

Ring rearrangement metathesis

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Ring rearrangement metathesis is a strategy for the introduction of new stereocenters to carbo- and heterocycles. This methodology has now been applied diastereoselectively. Depending on catalyst and substrate, moderate to good yields were observed. In these conversions diastereoisomeric ratios of up to 14:1 were obtained. more to: Ring rearrangement metathesis

Hydroamination

Hydroamination

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The construction of C-N-bonds is of great interest for both academic and industrial research. There is still need for the development of new catalytic systems as most of the well-known catalysts display drawbacks like air and moisture sensitivity. more to: Hydroamination

Cascade reactions

Cascade reactions

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Uleine-type alkaloids have been of synthetic interest over the past decades. Gilbertine was first discovered in 1982 and remained a challenge for synthetic organic chemists for more than 20 years. Gilbertine displays a much more complex structure than uleiene itself as it consists of a pentacyclic skeleton and an additional stereocenter. Our strategy was based on a cationic cascade reaction of a chiral tetrahydrocarbazole which was synthesized by a convenient Fischer indole synthesis. The stereochemistry was set up by a Shibasaki Michael addition. In summary the Uleine-type indole alkaloide (-)-Gilbertine has been synthesised starting from cyclohexenone in 17 steps in a 5.5 % overall yield. The key step, a cationic cascade cyclisation forming a tetrahydropyrane and piperidine ring and the pentacyclic framework in one step, was shown to be highly steroselective. more to: Cascade reactions

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