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A mechanistic study on modern palladium catalyst precursors as new gateways to Pd(0) in cationic Heck reactions
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Medicinal Chemistry, Organic Pharmaceutical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Medicinal Chemistry, Organic Pharmaceutical Chemistry.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Medicinal Chemistry. ORGFARM.
2008 (English)In: Tetrahedron, ISSN 0040-4020, E-ISSN 1464-5416, Vol. 64, no 8, 1808-1812 p.Article in journal (Refereed) Published
Abstract [en]

Electrospray ionization mass spectrometry (ESI-MS) was used as a means to directly identify catalytic cationic organopalladium species in ligand-controlled Heck reactions involving electron-rich olefins and different Pd-sources. In these high-temperature Heck arylations, the oxidative addition intermediates were observed as bidentate ligand chelated cationic aryl palladium species, suggesting that the used ligand attaches to the metal center at the very beginning of the catalytic cycle. This was also in agreement with the obtained regioisomeric profile of the isolated products. The investigation supports the standard Pd(0)/Pd(II) Heck mechanism and provides further insight regarding the conceivable composition of fundamental Pd(II) intermediates in an ongoing Heck reaction.

Place, publisher, year, edition, pages
2008. Vol. 64, no 8, 1808-1812 p.
Keyword [en]
ESI-MS, Heck, palladium, microwave
National Category
Pharmaceutical Sciences
URN: urn:nbn:se:uu:diva-95221DOI: 10.1016/j.tet.2007.11.111ISI: 000253620600028OAI: oai:DiVA.org:uu-95221DiVA: diva2:169350
Available from: 2006-11-23 Created: 2006-11-23 Last updated: 2013-07-04Bibliographically approved
In thesis
1. Fast Microwave-Enhanced Intra-, Pseudo-intra- and Intermolecular Heck Reactions
Open this publication in new window or tab >>Fast Microwave-Enhanced Intra-, Pseudo-intra- and Intermolecular Heck Reactions
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Heck reaction is one of the most appreciated methods for carbon-carbon bond formation. Due to its mildness and ability to be tuned by additives, it often leaves few alternative competitive reactions. It has also proven easy to develop the reaction conditions in an environmentally benign direction. Through the introduction of palladium chelating groups in olefinic precursors for the Heck reaction, it has been possible to direct the substitution in the following Heck arylation in favor of the terminal position with good regioselectivity. In this thesis, the concept has been utilized to produce a small array of drug-like compounds at useful yields under fast microwave-enhanced conditions utilizing the thermostable Herrmanns palladacycle. During the last decade, this, together with other palladacycles has become commonly employed as precatalyst for the Heck reaction. However, there have been conflicting opinions regarding the mechanisms governing its catalytic effect. A PdII-PdIV catalytic cycle has been suggested to be operative, in contrast to the classical Pd0-PdII cycle. In order to clarify the presence of such a mechanism, a set of Heck reactions was performed with the advent of different palladium precatalysts (classical and palladacycles), which revealed that the regiochemicαal substitution pattern is highly conserved, regardless of which precatalyst was employed, and thus, the same mechanism seems to be operative. This is also supported by data from ESI-MS investigations where all the reactions investigated gave rise to the same set of oxidative addition complexes. A crafted route to 3-aryl-1,2-cyclohexandiones has been developed in which 1,2-cyclohexandione is produced is situ from 2,3-epoxycyclohexanone, followed by Heck arylation. A diverse array of aryl bromides encompassing electron-rich, electron-poor, neutral and sterically hindered repressentatives has been successfully utilized to produce the corresponding products at useful yields.The intramolecular Heck reaction offers a route to quaternary carbonic centersand is being increasingly exploited in synthetic endeavors. However, the use of electron-rich olefinic precursors is only reported in a few cases. The implementation of one capto-dative and five electron-rich olefins has therefore been successfully subjected to Heck reaction conditions rendering the corresponding spiro compounds.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 74 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, ISSN 1651-6192 ; 45
Pharmaceutical chemistry, palladium, Heck reaction, chelation control, microwave, Farmaceutisk kemi
urn:nbn:se:uu:diva-7368 (URN)91-554-6742-3 (ISBN)
Public defence
2006-12-15, B41, BMC, Husargatan 3, Uppsala, 09:15
Available from: 2006-11-23 Created: 2006-11-23Bibliographically approved

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Sjöberg, PerLarhed, MatsNilsson, Peter
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