Journal
TETRAHEDRON
Volume 75, Issue 26, Pages 3579-3585Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.tet.2019.05.026
Keywords
Amino acid; Oxidation; Hydrogen atom transfer; N-hydroxyphthalimide
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Funding
- Ministero dell'Istruzione, dell'Universita e della Ricerca (MIUR)
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A kinetic study of the hydrogen atom transfer (HAT) reaction from a series of N-Boc- or N-Acetyl-protected amino acids to the phthalimide N-oxyl radical (PINO) was carried out to obtain information about reactivity and selectivity patterns. With amino acids containing aliphatic side chains, the 2nd order rate constants are of the same order of magnitude, in agreement with a HAT process involving the C alpha-H bond. Proline is the most reactive substrate suggesting that HAT process involves the C-delta-H bond instead of C-alpha-H bond. These results are confirmed by the product analysis of the aerobic oxidations of the corresponding N-Boc and N-Ac protected amino acids methyl esters promoted by N-hydroxyphthalimide. Comparison of our results with those reported for HAT reactions to other radical species indicates that PINO displays electrophilic characteristics that are intermediate between those observed for the more stable Br center dot radical and the more reactive cumyloxyl radical. (C) 2019 Elsevier Ltd. All rights reserved.
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