Polymer- und mizellar-gebundene N-heterocyclische Carbene als Nanoreaktoren für die organische Chemie und Studien zur Totalsynthese von Virgiboidin und Virgidivarin mittels Enin-Ringumlagerungs-Metathese [article]

Jochen Weckesser, Siegfried Blechert, Technische Universität Berlin, Technische Universität Berlin
2010
Two topics from the area of olefin metathesis were investigated in the course of this thesis. In the first part, monomers were synthesized for the generation of linear, amphiphilic blockcopolymers that carry N-heterocyclic carbenes (NHCs) in their hydrophobic block. These polymers were to be used as micellar nanoreactors, in which either a metal atom which is coordinated to the NHC displays the catalytic activity, or the free NHC itself functions as nucleophilic organocatalyst. Hence, numerous
more » ... t. Hence, numerous ROMP-monomers were synthesized which can be classified into three subgroups: Polar monomers, unpolar monomers and monomers which contain an NHC-precursor moiety or an NHC-metal-complex. All monomers are norbornene- or oxanorbornene-derivatives, whose starting materials are either commercially available or were prepared by Diels-Alder reactions or coupling reactions to norbornadiene. These monomers were polymerized in cooperation with the group of Prof. Buchmeiser with catalysts of the Grubbs- and Schrock-type. In a proof of principle, a Rh-catalyzed hydroformylation of 1-octene was successfully carried out in a micellar system. However, the Rh-atom was coordinated to a bipyridine ligand instead of an NHC. Furthermore, studies towards the enantioselective total synthesis of the two alkaloids virgiboidine and virgidivarine were carried out. The key step of the synthesis is the preparation of a dipiperidine skeleton in a single step via enyne ring rearrangement metathesis, starting from an appropriately substituted cyclopentene. The metathesis precursor can be prepared in few steps from commercially available (+)-(1R,4S)-4-hydroxycyclopent-2-enyl-acetate. Virgiboidine, a quinolizidine-alkaloid can be obtained in one step from virgidivarine by condensation. The synthesis is based on previous achievements by S. Schulz an M. Schaudt. The focus of this thesis lies on the selective functionalization of the terminal double bond of the 1,3-butadiene moiety of the product of the enyne ring rearrangement metathesis. Various oxidation m [...]
doi:10.14279/depositonce-2453 fatcat:uinwf7pplbamjpzito2ue6orkq