Molecules 2011, 16(1), 951-969; doi:10.3390/molecules16010951
Review

Palladium Catalyzed Allylic C-H Alkylation: A Mechanistic Perspective

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Received: 30 November 2010; in revised form: 13 January 2011 / Accepted: 18 January 2011 / Published: 21 January 2011
(This article belongs to the Special Issue Homogeneous Catalysis)
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract: The atom-efficiency of one of the most widely used catalytic reactions for forging C-C bonds, the Tsuji-Trost reaction, is limited by the need of preoxidized reagents. This limitation can be overcome by utilization of the recently discovered palladium-catalyzed C-H activation, the allylic C-H alkylation reaction which is the topic of the current review. Particular emphasis is put on current mechanistic proposals for the three reaction types comprising the overall transformation: C-H activation, nucleophillic addition, and re-oxidation of the active catalyst. Recent advances in C-H bond activation are highlighted with emphasis on those leading to C-C bond formation, but where it was deemed necessary for the general understanding of the process closely related C-H oxidations and aminations are also included. It is found that C-H cleavage is most likely achieved by ligand participation which could involve an acetate ion coordinated to Pd. Several of the reported systems rely on benzoquinone for re-oxidation of the active catalyst. The scope for nucleophilic addition in allylic C-H alkylation is currently limited, due to demands on pKa of the nucleophile. This limitation could be due to the pH dependence of the benzoquinone/hydroquinone redox couple. Alternative methods for re-oxidation that does not rely on benzoquinone could be able to alleviate this limitation.
Keywords: palladium; C-H activation; allylic alkylation; catalysis
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MDPI and ACS Style

Engelin, C.J.; Fristrup, P. Palladium Catalyzed Allylic C-H Alkylation: A Mechanistic Perspective. Molecules 2011, 16, 951-969.

AMA Style

Engelin CJ, Fristrup P. Palladium Catalyzed Allylic C-H Alkylation: A Mechanistic Perspective. Molecules. 2011; 16(1):951-969.

Chicago/Turabian Style

Engelin, Casper Junker; Fristrup, Peter. 2011. "Palladium Catalyzed Allylic C-H Alkylation: A Mechanistic Perspective." Molecules 16, no. 1: 951-969.

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