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首页> 外文期刊>Chemistry: A European journal >Palladium-catalysed [3+2] cycloaddition of alk-5-ynylidenecyclopropanes to alkynes: A mechanistic DFT study
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Palladium-catalysed [3+2] cycloaddition of alk-5-ynylidenecyclopropanes to alkynes: A mechanistic DFT study

机译：钯催化[3 + 2]烷基-5-亚萘基环丙烷与炔烃的加成反应：机理DFT研究

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摘要

The mechanism of the palladium-catalysed [3+2] intramolecular cycloaddition of alkylidenecyclopropanes to alkynes has been computationally explored at DFT level. The energies of the reaction intermediates and transition states for different possible pathways have been calculated in a model system that involves the use of PH3 as a ligand. The results obtained suggest that the most favourable reaction pathway involves the initial C-C oxidative addition of the cyclopropane to a Pd-0 complex to give an alkylidene-palladacyclobutane, which isomerises to a methylenepalladacyclobutane intermediate. Subsequent cyclisation by alkyne carbometallation, followed by reductive elimination affords the final product. An alternative mechanism consisting of a palladaene-type rear-rangement is less probable in terms of Gibbs energy, but cannot be fully discarded because it is competitive if one considers electronic energies. For substrates that present an ester group at the terminal position of the triple bond we have found an alternative, more favourable mechanistic route that explains why the [3+2] cycloaddition of these types of systems does not lead to the expected cycloadducts.
机译：在DFT级别上已通过计算探索了钯催化的亚烷基环丙烷向炔烃的[3 + 2]分子内环加成的机理。已在涉及使用PH3作为配体的模型系统中计算了不同中间体可能的反应中间体的能量和跃迁状态。所获得的结果表明，最有利的反应途径涉及将环丙烷最初的C-C氧化加成到Pd-0络合物上，以得到亚烷基-Palladacyclobutane异构化成亚甲基Palladacyclocyclobutane中间体。随后通过炔烃碳金属化进行环化，然后还原消除，得到最终产物。就吉布斯能量而言，由戊二烯类型的重排组成的另一种机制不太可能，但由于考虑到电子能量具有竞争性，因此无法完全抛弃。对于在三键末端具有酯基的底物，我们发现了另一种更有利的机理路线，该路线解释了为什么这些类型系统的[3 + 2]环加成反应不会产生预期的环加成物。

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