Cu-Catalyzed Dehydrogenative C–O Cyclization for the Synthesis of Furan-Fused Thienoacenes

Koichi Mitsudo*, Yoshiaki Kobashi, Kaito Nakata, Yuji Kurimoto, Eisuke Sato, Hiroki Mandai, and Seiji Suga*
Org. Lett. 2021, 23, 4322–4326.
DOI: 10.1021/acs.orglett.1c01256

Yoshiaki found this reaction conditions and Kaito finished this work. Whereas there have been reports on Pd- or Cu-catalyzed dehydrogenative C–O cyclizations to form furan and lactone rings, there has been no report on the synthesis of heteroaromatic fused furans. We achieved the first example of the synthesis of furan-fused thienoacenes via a Cu-catalyzed dehydrogenative C-O cyclization.

The key point is to use two solvents, NMP and EGM. The use of only one of the two was insufficient, but the reaction proceeds well in in the mixed of them. Further addition of toluene to the mixture gave better results.