Stereoselective rhodium-catalysed [2+2+2] Cycloaddition of linear allene-ene/yne-allene substrates: Reactivity and theoretical mechanistic studies

Ewelina Haraburda, Òscar Torres, Teodor Parella, Miquel Solà, Anna Pla-Quintana

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    Abstract

    Allene-ene-allene (2 and 5) and allene-yne-allene (3 and 7) N-tosyl and O-linked substrates were satisfactorily synthesised. The [2+2+2] cycloaddition reaction catalysed by the Wilkinson catalyst [RhCl(PPh3)3] was evaluated. Substrates 2 and 5, which bear a double bond in the central position, gave a tricyclic structure in a reaction in which four contiguous stereogenic centres were formed as a single diastereomer. The reaction of substrates 3 and 7, which bear a triple bond in the central position, gave a tricyclic structure with a cyclohexenic ring core, again in a diastereoselective manner. All cycloadducts were formed by a regioselective reaction of the inner allene double bond and, therefore, feature an exocyclic diene motif. A Diels-Alder reaction on N-tosyl linked cycloadducts 8 and 10 allowed pentacyclic scaffolds to be diastereoselectively constructed. The reactivity of the allenes on [2+2+2] cycloaddition reactions was studied for the first time by density functional theory calculations. This mechanistic study rationalizes the order in which the unsaturations take part in the catalytic cycle, the reactivity of the two double bonds of the allene towards the [2+2+2] cycloaddition reaction, and the diastereoselectivity of the reaction. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Original languageEnglish
    Pages (from-to)5034-5045
    JournalChemistry - A European Journal
    Volume20
    Issue number17
    DOIs
    Publication statusPublished - 22 Apr 2014

    Keywords

    • allenes
    • cycloaddition
    • density functional calculations
    • reaction mechanisms
    • rhodium

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    Haraburda, E., Torres, Ò., Parella, T., Solà, M., & Pla-Quintana, A. (2014). Stereoselective rhodium-catalysed [2+2+2] Cycloaddition of linear allene-ene/yne-allene substrates: Reactivity and theoretical mechanistic studies. Chemistry - A European Journal, 20(17), 5034-5045. https://doi.org/10.1002/chem.201304463