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Mousavi, Mohammad S.; Di Mola, Antonia; Pierri, Giovanni; Tedesco, Consiglia; Hensinger, Magenta J.; Sun, Aijia; Wang, Yilan; Mayer, Peter ORCID logoORCID: https://orcid.org/0000-0002-1847-8032; Ofial, Armin R. ORCID logoORCID: https://orcid.org/0000-0002-9600-2793 und Massa, Antonio (30. April 2024): Lactone Enolates of Isochroman-3-ones and 2‑Coumaranones: Quantification of Their Nucleophilicity in DMSO and Conjugate Additions to Chalcones. In: Journal of Organic Chemistry, Bd. 89, Nr. 10: S. 6915-6928 [PDF, 2MB]

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Abstract

Owing to stereoelectronic effects, lactones often deviate in reactivity from their open-chain ester analogues as demonstrated by the CH acidity (in DMSO) of 3-isochromanone (pKa = 18.8) and 2-coumaranone (pKa = 13.5), which is higher than that of ethyl phenylacetate (pKa = 22.6). We have now characterized the reactivity of the lactone enolates derived from 3-isochromanone and 2-coumaranone by following the kinetics of their Michael reactions with p-quinone methides and arylidenemalonates (reference electrophiles) in DMSO at 20 °C. Evaluation of the experimentally determined second-order rate constants k2 by the Mayr–Patz equation, lg k2 = sN(N + E), furnished the nucleophilicity parameters N (and sN) of the lactone enolates. By localizing their position on the Mayr nucleophilicity scale, the scope of their electrophilic reaction partners becomes predictable, and we demonstrate a novel catalytic methodology for a series of carbon–carbon bond-forming reactions of lactone enolates with chalcones under phase transfer conditions in toluene.

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