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 (pK(a) = 18.8) and 2-coumaranone (pK(a) = 13.5), which is higher than that of ethyl phenylacetate (pK(a) = 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 degrees C. Evaluation of the experimentally determined second-order rate constants k(2) by the Mayr-Patz equation, lg k(2) = s(N)(N + E), furnished the nucleophilicity parameters N (and s(N)) 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.
Lactone Enolates of Isochroman-3-ones and 2-Coumaranones: Quantification of Their Nucleophilicity in DMSO and Conjugate Additions to Chalcones
Mousavi, Mohammad Sadeq;Di Mola, Antonia;Pierri, Giovanni;Tedesco, Consiglia;Massa, Antonio
2024
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 (pK(a) = 18.8) and 2-coumaranone (pK(a) = 13.5), which is higher than that of ethyl phenylacetate (pK(a) = 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 degrees C. Evaluation of the experimentally determined second-order rate constants k(2) by the Mayr-Patz equation, lg k(2) = s(N)(N + E), furnished the nucleophilicity parameters N (and s(N)) 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.File | Dimensione | Formato | |
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