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Biomimetic Reductive Cleavage of Keto Aryl Ether Bonds by Small‐Molecule Thiols
Author(s) -
Klinger Grace E.,
Zhou Yuting,
Hao Pengchao,
Robbins Jacob,
Aquilina Jake M.,
Jackson James E.,
Hegg Eric L.
Publication year - 2019
Publication title -
chemsuschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.412
H-Index - 157
eISSN - 1864-564X
pISSN - 1864-5631
DOI - 10.1002/cssc.201901742
Subject(s) - chemistry , aryl , ether , nucleophile , ether cleavage , thioether , thiol , depolymerization , redox , organic chemistry , reductive elimination , photochemistry , catalysis , alkyl
The nucleophilic and reductive properties of thiolates and thiols make them ideal candidates as redox mediators via the thiol/disulfide couple. One mechanism for biological lignin depolymerization entails reduction of keto aryl ether bonds by an S N 2 mechanism with the thiol redox mediator glutathione. In this study, mimicking this chemistry in a simple protein‐ and metal‐free process, several small organic thiols are surveyed for their ability to cleave aryl keto ethers that model the β‐ O ‐4 linkages found in partially oxidized lignin. In polar aprotic solvents, β‐mercaptoethanol and dithiothreitol yielded up to 100 % formation of phenol and acetophenone products from 2‐phenoxyacetophenone, but not from its reduced alcohol congener. The effects of reaction conditions and of substituents on the aryl rings and the keto ether linkage are assessed. These results, together with activation barriers computed by quantum chemical simulations and direct observation of the expected intermediate thioether, point to an S N 2 mechanism. This study confirms that small organic thiols can reductively break down lignin‐relevant keto aryl ether linkages.