2-Methylene-1,2-dihydropyridines (2-pyNHOs): highly nucleophilic enamines

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dc.contributor.authorBehnke, Annika
dc.contributor.authorEitzinger, Andreas
dc.contributor.authorHe, Yijie
dc.contributor.authorAntoni, Patrick W.
dc.contributor.authorOfial, Armin R.
dc.contributor.authorHansmann, Max M.
dc.date.accessioned2025-04-25T13:57:23Z
dc.date.available2025-04-25T13:57:23Z
dc.date.issued2024-04-30
dc.description.abstractThe high reactivity of 2-methylene-1,2-dihydropyridines also known as 2-methylpyridinium derived N-heterocyclic olefins (2-pyNHOs) has been recognized in organic synthesis, yet a quantification of their nucleophilicity is lacking. Herein we used stopped-flow photometry to determine the nucleophilicity of a series of 2-pyNHOs from the kinetics of their reactions with quinone methides and benzhydrylium ions as reference electrophiles in four organic solvents at 20 °C. The kinetic data was evaluated by using the Mayr-Patz equation, lg k(20 °C)=sN(N+E), which gave nucleophilicity parameters N (and sN). With N in the range of 19.4–21.2 (in DMSO), 2-pyNHOs exceed the reactivity of classical enamines, such as pyrrolidino-cyclopent-1-ene. The addition of 2-pyNHOs to quinone methides resulted in the formation of zwitterionic adducts with pyridinium and phenolate moieties. Subsequent tautomerization yielded entirely neutral pyridine-2(1H)-ylidene-phenol species in several cases. Formation of the zwitterionic adducts from 2-pyNHOs and neutral electrophiles was almost equally fast in the polar solvents acetonitrile and DMSO, but proceeded one to two orders of magnitude slower in the less polar solvents dichloromethane or THF.en
dc.identifier.urihttp://hdl.handle.net/2003/43682
dc.identifier.urihttp://dx.doi.org/10.17877/DE290R-25455
dc.language.isoen
dc.relation.ispartofseriesEuropean journal of organic chemistry; 27(39)
dc.rights.urihttps://creativecommons.org/licenses/by/4.0/
dc.subjectkineticsen
dc.subjectnucleophilicityen
dc.subjectlinear free energy relationshipsen
dc.subjectN-heterocyclic olefinsen
dc.subjectC−C bond polarizationen
dc.subject.ddc540
dc.title2-Methylene-1,2-dihydropyridines (2-pyNHOs): highly nucleophilic enaminesen
dc.typeText
dc.type.publicationtypeResearchArticle
dcterms.accessRightsopen access
eldorado.openaire.projectidentifierinfo:eu-repo/grantAgreement/EC/HE/101077332/EU/NAME/CC-CHARGED
eldorado.secondarypublicationtrue
eldorado.secondarypublication.primarycitationA. Behnke, A. Eitzinger, Y. He, P. W. Antoni, A. R. Ofial, M. M. Hansmann, Eur. J. Org. Chem. 2024, 27, e202400373. https://doi.org/10.1002/ejoc.202400373
eldorado.secondarypublication.primaryidentifierhttps://doi.org/10.1002/ejoc.202400373

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