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Control of Selectivity in Palladium-Catalyzed Oxidative Carbocyclization/Borylation of Allenynes
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.
2013 (English)In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 52, no 24, 6283-6287 p.Article in journal (Refereed) Published
Abstract [en]

In control: A highly selective carbocyclization/borylation of allenynes with bis(pinacolato)diboron (B2pin2) under palladium catalysis and with p-benzoquinone (BQ) as the oxidant was developed. The use of either LiOAc⋅2 H2O with 1,2-dichloroethane (DCE) as the solvent or BF3⋅Et2O together with THF is crucial for the selective formation of borylated trienes and vinylallenes, respectively.

Place, publisher, year, edition, pages
2013. Vol. 52, no 24, 6283-6287 p.
Keyword [en]
allenes, boronates, cyclization, oxidation, palladium
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:su:diva-90111DOI: 10.1002/anie.201301167ISI: 000320375800028OAI: oai:DiVA.org:su-90111DiVA: diva2:622745
Funder
EU, European Research Council, 247014Swedish Research CouncilKnut and Alice Wallenberg FoundationThe Wenner-Gren FoundationBerzelii Centre EXSELENT
Note

AuthorCount: 3;

Available from: 2013-05-23 Created: 2013-05-23 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Palladium(II)-Catalyzed Oxidative Carbocyclization/Functionalization of Allenynes
Open this publication in new window or tab >>Palladium(II)-Catalyzed Oxidative Carbocyclization/Functionalization of Allenynes
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Palladium catalysis has emerged as an outstanding tool in synthetic organic chemistry for the mild and selective formation of carbon-carbon and carbon-heteroatom bonds. This thesis has been directed towards the extension of palladium(II)-catalyzed carbocyclization chemistry under oxidative conditions. An oxidative carbocyclization/functionalization methodology utilizing boron-containing transmetalation reagents was exploited to convert 1,5-allenynes into either arylated or borylated carbocycles. Two protocols were developed that use minimal amounts of Pd(OAc)2, stoichiometric para-benzoquinone as the oxidant and either bis(pinacolato)diboron or different arylboronic acids under mild conditions. A wide substrate scope is applicable to both methods. When the allenyne substrate bears a propargylic hydrogen, two isomeric functionalized carbocycles can be formed. By controlling the reaction conditions the reaction can be directed towards either of these two isomeric products. Kinetic isotope effect studies suggest that the mechanism leading to the different products proceeds through allylic or propargylic C-H bond cleavage, respectively. Moreover, it was observed that water has an interesting effect on the product selectivity when arylboronic acids are used in the oxidative carbocyclization of allenynes.

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University, 2013. 59 p.
National Category
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-88935 (URN)
Presentation
2013-04-23, Magnéli Hall, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 11:00
Opponent
Supervisors
Available from: 2013-05-22 Created: 2013-04-08 Last updated: 2013-05-23Bibliographically approved
2. Palladium(II)-Catalyzed Oxidative Carbocyclization/Functionalization of Allenynes
Open this publication in new window or tab >>Palladium(II)-Catalyzed Oxidative Carbocyclization/Functionalization of Allenynes
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.
Keyword
palladium catalysis, oxidation, carbocyclization, allenynes, boron reagents, kinetics, selectivity, reaction mechanism
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-108587 (URN)978-91-7649-019-8 (ISBN)
Public defence
2014-12-04, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.

Available from: 2014-11-12 Created: 2014-10-30 Last updated: 2014-11-21Bibliographically approved

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