C. De Luca, D. Zanetti, T. Battisti, R. R. Ferreira, S. Lopez, A. H. McMillan, S. C. Lesher-Pérez, L. Maggini, D. Bonifazi.
Chem. Eur. J. 2023, e202302129.
The typical Birch reduction transforms arenes into 1,4-cyclohexadienes using alkali metals, an alcohol as a proton source, and an amine as solvent. Capitalizing on the strong photoreductive properties of peri-xanthenoxanthene (PXX), herein we report the photocatalyzed “Birch-type” reduction of acenes employing visible blue light irradiation at room temperature in the presence of air. Upon excitation at 405 or 460 nm in the presence of a mixture of N,N-diisopropylethylamine (DIPEA)and trifluoromethanesulfonimide (HNTf2) in DMSO, PXX photocatalyzes the selective reduction of full-carbon acene derivatives (24–75%). Immobilization of PXX onto polydimethylsiloxane (PDMS) beads (PXX-PDMS) allowed the use of the catalyst in heterogeneous batch reactions, yielding 9-phenyl-9,10-dihydroanthracene in high yields (68%). The catalyst could be easily recovered and reused, with no notable catalytic performance drop observed after five reaction cycles. Integration of the PXX-PDMS beads into a microreactor enabled the reduction of acenes under continuous flow conditions, there by validating the sustainability and scalability of this heterogeneous phase approach.