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Carbocations as Lewis Acid Catalysts in Diels-Alder and Michael Addition Reactions
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.ORCID iD: 0000-0003-1933-4193
2014 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, no 4, 1066-1072 p.Article in journal (Refereed) Published
Abstract [en]

In general, Lewis acid catalysts are metal-based compounds that owe their reactivity to a low-lying empty orbital. However, one potential Lewis acid that has received negligible attention as a catalyst is the carbocation. We have demonstrated the potential of the carbocation as a highly powerful Lewis acid catalyst for organic reactions. The stable and easily available triphenylmethyl (trityl) cation was found to be a highly efficient catalyst for the Diels-Alder reaction for a range of substrates. Catalyst loadings as low as 500ppm, excellent yields, and good endo/exo selectivities were achieved. Furthermore, by changing the electronic properties of the substituents on the tritylium ion, the Lewis acidity of the catalyst could be tuned to control the outcome of the reaction. The ability of this carbocation as a Lewis acid catalyst was also further extended to the Michael reaction.

Place, publisher, year, edition, pages
2014. Vol. 20, no 4, 1066-1072 p.
Keyword [en]
carbocations, catalysis, Diels-Alder reactions, Michael addition, organocatalysis, tritylium ions
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-141061DOI: 10.1002/chem.201304160ISI: 000329548000022ScopusID: 2-s2.0-84892615130OAI: diva2:695578
Swedish Research Council

QC 20140211

Available from: 2014-02-11 Created: 2014-02-07 Last updated: 2014-04-25Bibliographically approved
In thesis
1. Metal-Free Catalysis for Efficient Synthesis
Open this publication in new window or tab >>Metal-Free Catalysis for Efficient Synthesis
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The strength of efficient metal-free catalysis will be examined in this thesis. Efforts towards more sustainable processes will be demonstrated through implementation of strategies that meet several of the 12 principles of Green Chemistry.In the first part, a stereoselective total synthesis of multiple alkaloids from the Corynantheine and Ipecac families together with their non-natural analogues will be disclosed. A highly efficient, common synthetic strategy is applied leading to high overall yields starting from easily available starting material. Overall operational simplicity and sustainability have been the main focus. Time-consuming and waste-generating isolations and purifications of intermediates have been minimized, as well as the introduction of protection-group chemistry. Moreover, the first example of the total synthesis of Hydroxydihydrocorynantheol together with its non-natural epimer has been accomplished in multi-gram scale without protection groups and without a single isolation or purification step in high overall yield and diastereoselectivity.In the second part, carbocations will be presented as highly effective and versatile non-metal Lewis acid catalysts. Lewis acidity-tuning of carbocations will be introduced and applied in several reactions to suppress competing reactions. Finally, the broad scope of carbocation catalyzed transformations will be exposed.At large, evident progress has been made towards more sustainable chemistry.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2014. 69 p.
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:15
Homogeneous c atalysi s, O rga nocatalysis, Green C hemistry, T o tal S ynthesis, A lkaloids, A symmetric S ynthesis, N on - metal Lewis acid s, C arbocations, Sustainability
National Category
Organic Chemistry
Research subject
urn:nbn:se:kth:diva-144577 (URN)978-91-7595-110-2 (ISBN)
Public defence
2014-05-08, E3, Osquars Backe 14, 5 tr, Stockholm, 13:00 (English)

QC 20140425

Available from: 2014-04-25 Created: 2014-04-24 Last updated: 2014-04-25Bibliographically approved

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