Science of Synthesis

Wang, M.; Li, P.; Wang, L., Science of Synthesis: Photocatalysis in Organic Synthesis, (2018) 1, 335.

Lignocellulose exists widely in plant cell walls and lignin is the largest renewable feedstock containing an aromatic backbone; hence, the development of efficient processes for its exploitation as a renewable resource is a well-recognized objective.[‌93‌,‌94‌] Although considerable effort has been devoted to chemical depolymerization of lignin,[‌95‌–‌100‌] its rigid, irregular, and highly cross-linked structure renders effective degradation a challenging goal. Recently, a novel approach toward the valorization of lignin and related systems has been developed by combining photoredox and palladium catalysis, which allows for the efficient oxidation of lignin-related systems at room temperature. Some simplified β-O-4 model systems ‌44‌ are oxidized to the corresponding ketones ‌45‌ in high yields using iridium photocatalyst ‌43‌ {[Ir{dF(CF3)ppy}2(dtbbpy)]PF6; dF(CF3)ppy = 3,5-difluoro-2-[5-(trifluoromethyl)pyridin-2-yl]phenyl; dtbbpy = 4,4′-di-tert-butyl-2,2′-bipyridyl} and sodium persulfate. This method constitutes a vital step toward converting lignin into value-added, low-molecular weight aromatics (‌Scheme 12‌).[‌101‌]

‌Meeeee 88‌ Meeeeeeee Meeee ee eee Meeeeeeee/Meeeeee-Meeeeeeee Meeeeeeee ee Meeeee Meeee Meeeeee[‌888‌]

‌Meeeeeeeeee 88‌

Meeeeeeeeeee Meeeeeeee

8-(8-Meeeeeeeeeeeee)-8-(8-eeeeeeeeeeeee)eeeee-8-eee (‌88‌, M8 = M8 = MMe; M8 = M8 = M8 = M8 = M8 = M); Meeeeee Meeeeeeee:[‌888‌]

M eeeee-eeeeeeee eeeee eee eeeeeee eeee eeeeeee eeeeeeeeee eeeeeeee ‌88‌ (8.8 ee, 8.8 µeee, 8 eee%), Me(MMe)8 (8.8 ee, 88 µeee, 88 eee%), 8-(8-eeeeeeeeeeeeee)-8-(8-eeeeeeeeeeeee)eeeee-8-ee (‌88‌, M8 = M8 = MMe; M8 = M8 = M8 = M8 = M8 = M; 88 ee, 8.88 eeee), Me8M8M8 (888 ee, 8.88 eeee, 8 eeeee), eee MMM (8.8 eM). Mee eeeeeeeee eeee eee eeeeeeee ee eeeeee–eeee–eeee eeeeee (8 ×) eee eee eeeee eee eeeeeeeeee eeee M8. Mee eeeeeee eee eeee eeeeeeeeee eeee e eeee MMM eeeee (8.8 M) ee e eeeeee eeeeee eee eeeee (ee. 8 ee eeee eee eeeee) eee eeeeeee ee ee eee 88 e. Meeee eeeeeeeeee ee eee eeeeeeee, MM8Me8 eee M8M eeee eeeee eee eee eeeeee eeee eeeeeeeee. Mee eeeeeee eeeee eee eeeeeeeee eeee MM8Me8 eee eee eeeeeeee eeeeeee eeeeee eeee eeeeee eeee 8% ee MeMe eee eeee eeeee, eeeee (Me8MM8), eeeeeeee, eee eeeeeeeeeeee eeeee eeeeeee eeeeeeee. Mee eeeee eeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeeee (eeeeeee/MeMMe 8:8) ee eeeeee eee eeeeeee ee e eeeee eeeee; eeeee: 88 ee (88%).

References