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Issue 31, 2012
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Mechanistic study on the palladium-catalyzed (3 + 2) intramolecular cycloaddition of alk-5-enylidenecyclopropanes

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Abstract

The intramolecular (3 + 2) cycloaddition of alkenylidenecyclopropanes to alkenes under palladium catalysis provides a practical and stereoselective entry into a variety of interesting bicycles. The reaction outcome and stereoselectivity of the process are somewhat dependent on the characteristics of the substrate and of the palladium ligand, which is not easy to justify on the basis of the current mechanistic understanding. We therefore decided to study the different mechanistic alternatives from a theoretical point of view. The energies of the reaction intermediates and transition states for different possible pathways have been explored at DFT level in a model system, and using PH3 and P(OMe)3 as ligands. The results obtained suggest that the most favourable reaction pathway involves an initial oxidative addition of Pd(0) at the distal position of the cyclopropane to afford a palladacyclobutane intermediate. The evolution of this intermediate into the final cycloadduct can occur following different paths, the most favorable depending on the configuration and substitution of the alkene cycloaddition partner, and the number of ancillary ligands coordinated to Pd. The computational results are consistent with the experimental observations and provide the basis for proposing which would be the operative mechanistic pathway in different cases. The results also allow us to explain the stereochemical divergences observed in some of the reactions.

Graphical abstract: Mechanistic study on the palladium-catalyzed (3 + 2) intramolecular cycloaddition of alk-5-enylidenecyclopropanes

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Publication details

The article was received on 17 Oct 2011, accepted on 18 Jun 2012 and first published on 03 Jul 2012


Article type: Paper
DOI: 10.1039/C2DT11955B
Dalton Trans., 2012,41, 9468-9481

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    Mechanistic study on the palladium-catalyzed (3 + 2) intramolecular cycloaddition of alk-5-enylidenecyclopropanes

    R. García-Fandiño, M. Gulías, J. L. Mascareñas and D. J. Cárdenas, Dalton Trans., 2012, 41, 9468
    DOI: 10.1039/C2DT11955B

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