Palladium(II)-Catalyzed Oxidative Carbocyclization/Functionalization of Allenynes
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
The selective formation of carbon-carbon bonds constitutes a key transformation in organic synthesis with useful applications in pharmaceutical or material industry. A particularly versatile tool for carbon-carbon as well as carbon-heteroatom bond formation is palladium catalysis, which allows for mild and selective routes even towards complex structures.
The work in this thesis describes the development and the mechanistic investigation of a palladium(II)-catalyzed oxidative carbocyclization/functionalization methodology, which converts 1,5-allenynes into either arylated or borylated carbocycles. To this end, either boronic acids or B2pin2 are employed and 1,4-benzoquinone serves as the stoichiometric oxidant. These protocols provide access to two products, a cyclic triene and a cyclic vinylallene. Their formation is dependent on the substrate structure as the latter product requires a propargylic C–H bond to be present in the substrate. Based on kinetic isotope effects, mechanisms involving either an initial allenic or propargylic C–H abstraction, respectively, were proposed. Full control of product selectivity to give either trienes or vinylallenes was achieved by modifying the reaction conditions with additives. Using substoichiometric amounts of BF3·OEt2 leads selectively to borylated or arylated vinylallenes. Under arylating conditions the reaction is zero order in allenyne and oxidant, and first order in phenylboronic acid. Transmetalation and, to some extent, propargylic C–H cleavage were found to be turnover-limiting. The selective reaction towards functionalized trienes was achieved by addition of either substoichiometric LiOAc·2H2O (borylation) or excess amounts of H2O (arylation). For the latter case, a kinetic study revealed an unusually slow catalyst activation. Lower concentrations of H2O gave product mixtures, and it was shown that vinylallenes are formed with either boronic acid or boroxine, whereas the formation of trienes requires boronic acid.
Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University , 2014. , 95 p.
palladium catalysis, oxidation, carbocyclization, allenynes, boron reagents, kinetics, selectivity, reaction mechanism
Research subject Organic Chemistry
IdentifiersURN: urn:nbn:se:su:diva-108587ISBN: 978-91-7649-019-8OAI: oai:DiVA.org:su-108587DiVA: diva2:759706
2014-12-04, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 14:00 (English)
Cárdenas, Diego J., Professor
Bäckvall, Jan-Erling, Professor
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.2014-11-122014-10-302014-11-21Bibliographically approved
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