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Mechanism of Iodine(III)‐Promoted Oxidative Dearomatizing Hydroxylation of Phenols: Evidence for a Radical‐Chain Pathway
Author(s) -
Kraszewski Karol,
Tomczyk Ireneusz,
Drabinska Aneta,
Bienkowski Krzysztof,
Solarska Renata,
Kalek Marcin
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202002026
Subject(s) - chemistry , hypervalent molecule , nucleophile , hydroxylation , phenols , umpolung , radical , reagent , photochemistry , organic chemistry , catalysis , enzyme
The oxidative dearomatization of phenols with the addition of nucleophiles to the aromatic ring induced by hypervalent iodine(III) reagents and catalysts has emerged as a highly useful synthetic approach. However, experimental mechanistic studies of this important process have been extremely scarce. In this report, we describe systematic investigations of the dearomatizing hydroxylation of phenols using an array of experimental techniques. Kinetics, EPR spectroscopy, and reactions with radical probes demonstrate that the transformation proceeds by a radical‐chain mechanism, with a phenoxyl radical being the key chain‐carrying intermediate. Moreover, UV and NMR spectroscopy, high‐resolution mass spectrometry, and cyclic voltammetry show that before reacting with the phenoxyl radical, the water molecule becomes activated by the interaction with the iodine(III) center, causing the Umpolung of this formally nucleophilic substrate. The radical‐chain mechanism allows the rationalization of all existing observations regarding the iodine(III)‐promoted oxidative dearomatization of phenols.