A kinetic study of the hydrogen atom transfer (HAT) reactions from nitrogen-containing heterocycles (secondary and tertiary lactams, 2-imidazolidinones, 2-oxazolidinones, and succinimides) to the cumyloxyl radical has been carried out employing laser flash photolysis with ns time resolution. HAT occurs from the C-H bonds that are α to nitrogen, activated by hyperconjugative overlap with the N-C═O π system. In the lactam series, the second-order HAT rate constant (kH) was observed to decrease by a factor of ∼4 going from the five- and six-membered ring derivatives to the eight-membered ones, a behavior that was rationalized on the basis of a reduced extent of hyperconjugative activation associated to the greater flexibility of the larger rings compared to the smaller ones. In the five-membered-ring substrate series, the kH values were observed to increase by >3 orders of magnitude on going from succinimide to 2-imidazolidinones, a behavior that was explained in terms of the divergent contribution of hyperconjugative activation and deactivating electronic effects determined by ring functionalities. The results are discussed in the framework of the development of HAT-based C-H bond functionalization procedures.

Galeotti, M., Trasatti, C., Sisti, S., Salamone, M., Bietti, M. (2022). Factors governing reactivity and selectivity in hydrogen atom transfer from C(sp3)-H bonds of nitrogen-containing heterocycles to the cumyloxyl radical. JOURNAL OF ORGANIC CHEMISTRY, 87(11), 7456-7463 [10.1021/acs.joc.2c00955].

Factors governing reactivity and selectivity in hydrogen atom transfer from C(sp3)-H bonds of nitrogen-containing heterocycles to the cumyloxyl radical

Salamone M.
;
Bietti M.
2022-01-01

Abstract

A kinetic study of the hydrogen atom transfer (HAT) reactions from nitrogen-containing heterocycles (secondary and tertiary lactams, 2-imidazolidinones, 2-oxazolidinones, and succinimides) to the cumyloxyl radical has been carried out employing laser flash photolysis with ns time resolution. HAT occurs from the C-H bonds that are α to nitrogen, activated by hyperconjugative overlap with the N-C═O π system. In the lactam series, the second-order HAT rate constant (kH) was observed to decrease by a factor of ∼4 going from the five- and six-membered ring derivatives to the eight-membered ones, a behavior that was rationalized on the basis of a reduced extent of hyperconjugative activation associated to the greater flexibility of the larger rings compared to the smaller ones. In the five-membered-ring substrate series, the kH values were observed to increase by >3 orders of magnitude on going from succinimide to 2-imidazolidinones, a behavior that was explained in terms of the divergent contribution of hyperconjugative activation and deactivating electronic effects determined by ring functionalities. The results are discussed in the framework of the development of HAT-based C-H bond functionalization procedures.
2022
Pubblicato
Rilevanza internazionale
Articolo
Esperti anonimi
Settore CHIM/06 - CHIMICA ORGANICA
English
Galeotti, M., Trasatti, C., Sisti, S., Salamone, M., Bietti, M. (2022). Factors governing reactivity and selectivity in hydrogen atom transfer from C(sp3)-H bonds of nitrogen-containing heterocycles to the cumyloxyl radical. JOURNAL OF ORGANIC CHEMISTRY, 87(11), 7456-7463 [10.1021/acs.joc.2c00955].
Galeotti, M; Trasatti, C; Sisti, S; Salamone, M; Bietti, M
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/313586
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