Ab initio multireference study of Hetero-Diels-Alder reaction of buta-1,3-diene with alkyl glyoxylates
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Hetero-Diels-Alder (HDA) reaction of methyl glyoxylate with buta-1,3-diene has been investigated using multireference methods (complete active space SCF and multi-reference perturbation theory) and compared with several single-reference methods (including DFT) often used in calculations of catalysed [4+2] cycloadditions. Concerted and stepwise mechanisms, found in the literature, are compared. It is shown, that the stepwise mechanism may be a result of choosing unbalanced active space. Such choice leads to very close singlet and triplet states in the intermediate geometry - an artificial effect, that disappears if properly balanced active space is used (here, we use active space of 12 orbitals and 12 electrons). Conclusions concerning the mechanism and usefulness of the applied methodology are drawn, which might be important for theoretical investigation of stereoselectivity and specificity of catalysts for the HDA reaction.
KeywordsComplete active space - self consistent field method [4+2] cycloaddition Density functional theory Hetero-Diels-Alder reaction mechanism
Authors would like to acknowledge Wroclaw University of Technology, where the work was performed. This research is supported by the Marie Curie European Reintegration Grant (MERG-CT-2004–516486). B. Szefczyk would like to thank the Foundation for Polish Science for a fellowship. Calculations have been performed at Wroclaw (WCSS), Poznań (PSNC) and Warsaw (ICM) Supercomputer Centres. Authors are grateful to Prof. Janusz Jurczak and Dr Piotr Kwiatkowski from the Institute of Organic Chemistry, Polish Academy of Science for suggesting these interesting topics and fruitful discussions.
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