バイオマスの有効利用を指向した光と金属触媒を用いる炭素－炭素結合切断反応の開発

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A new light/copper relayed system is developed for aerobic oxidative fragmentation of lignin model compounds having beta-O-4 and beta-1 linkage. Lignin model compounds are successfully broken down with an enhanced reaction efficiency and different product distribution in comparison to thermal copper-catalyzed aerobic degradation.In this study, we used the simple compound having a beta-O-4 linage as the model substrate because it represents the most abundant repeating unit existing in lignin and the investigation on its behavior toward light and a copper catalyst would provide us with an insight into a depolymerization process of native lignin under similar conditions. When the model substrate in 1,2-dichloroethane was irradiated with a blue LEDs lamp under air in the presence of Mes-Acr+ BF4-(2.0 mol %),copper(II) acetate (20 mol %), and sodium acetate (2.0 equiv), the substrate was consumed after 12 h. 3,4-Dimethoxybenzaldehyde and 2-methoxyphenyl formate were obtained in 66% isolated yield and 56% GC yield, respectively. Thus, carbon-carbon bonds contained in the beta-O-4 linage is cleaved. Next, the conditions for aerobic fragmentation were applied to another family of lignin model compound having a beta-1 linkage, which is the second most abundant repeating unit found in lignin. It was proved to be also viable substrate. Thus, our photo-catalyzed system could also be applied for lignin model compounds having a beta-1 linkage.