Abstract
N-Heterocyclic carbenes (NHCs), which were first isolated in the early 1990s, have received a great deal of scientific attention as ligands for transition metal complexes and organocatalysts for more than a decade. Organocatalysis by NHCs primarily involves the reaction of carbonyl compounds, particularly the umpolung of aldehydes, although we and others have been developing the reactions and the polymerizations of Michael acceptors. This review focuses on the NHC-catalyzed transformations of Michael acceptors that were developed by our research group, including (1) tail-to-tail dimerization of a wide variety of substrates, (2) cyclotetramerization of acrylates, (3) tandem oxa-Michael addition and head-to-tail dimerization of methacrolein and (4) oxa-Michael addition polymerization of hydroxyl-functionalized acrylates. For the former two reactions, the NHCs turn the β-carbon of the Michael acceptors into nucleophilic sites (umpolung), thereby generating the deoxy-Breslow intermediate and enabling bond formation between the β-carbon and electrophiles. The latter two reactions are based on the O–C bond formation between alcohols and Michael acceptors, in which the NHC catalysts act as a Lewis base. Thus, the use of NHC catalysts allowed new modes of reactivity of Michael acceptors other than the conventional addition polymerizations.
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Acknowledgements
I thank Professor Masato Suzuki and Professor Koji Takagi of the Nagoya Institute of Technology for their helpful discussions. I also acknowledge Mr Atsushi Washio, Mr Yoshiya Ota, Mr Shintaro Shimakawa, Ms Akiho Katada, Mr Yusuke Tochigi, Mr Terumasa Kato, Ms Shoko Namera and Mr Masanori Nakazawa for their experimental contributions. This work was partially supported by Grant-in-Aid for Scientific Research for Young Scientists (B) No. 24750102, the Hibi Science Foundation, and the Toukai Foundation for Technology.
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Matsuoka, Si. N-Heterocyclic carbene-catalyzed dimerization, cyclotetramerization and polymerization of Michael acceptors. Polym J 47, 713–718 (2015). https://doi.org/10.1038/pj.2015.59
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DOI: https://doi.org/10.1038/pj.2015.59
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