Reductive Photoenzymatic O-Demethylation of Aryl Methyl Ethers and Lignin Monoaromatics Produces Methane

O-Demethylation of aryl methyl ethers is a highly desirable reaction because of the wide distribution of aryl methyl esters in nature and valuable phenol compounds obtained as products. However, this reaction requires harsh conditions in organic chemistry. To date, the reported enzymatic methods either require methyl acceptors or produce undesired side products. Here, we design a reductive photoenzymatic system that achieves the O-demethylation of aryl methyl ethers, including methoxyflavones, in up to quantitative yields. An equal amount of methane was produced without the need for any methyl acceptors. Given that lignin contains numerous aryl methyl ether groups and that O-demethylation is a crucial and challenging step for lignin valorization, we applied our strategy to the demethylation of alkaline pretreated liquor (APL) of lignin. Aryl methyl ethers in the APL were efficiently demethylated to produce phenols and methane. A mechanistic study revealed that a methyl radical was involved in the reaction. These data illustrate the great potential of our strategy for the O-demethylation of aryl methyl ethers, lignin valorization, and methane production from a renewable source.