C–H-Activated Direct Arylation of Strong Benzothiadiazole and Quinoxaline-Based Electron Acceptors

Electron
acceptors are important components of π-conjugated
materials, but the strong electron-withdrawing properties of the required
synthetic intermediates often make them poor substrates in synthetic
schemes designed around conventional organometallic cross-coupling.
Here, strong benzodiimine-based acceptors, including 5,6-difluoro­[2,1,3]­benzothiadiazole,
5,6-dicyano­[2,1,3]­benzothiadiazole, 5,6-dicyanobenzo­[d]­[1,2,3]­triazole, 6,7-dicyanoquinoxaline, and 6,7-dinitroquinoxaline,
are shown to undergo facile palladium-catalyzed C–H direct
arylation with a variety of bromoarenes in moderate to high yields.
The electrochemical characteristics of di-2-thienyl derivatives synthesized
using this methodology are compared and suggest that, in an electron-transfer
sense, 5,6-dicyano­[2,1,3]­benzothiadiazole is a comparably strong acceptor
to benzo­[1,2-c:4,5-c′]­bis­[1,2,5]­thiadiazole.
The synthetic results suggest that high electron-withdrawing ability,
which has traditionally limited reaction yields and structural variety
in organic electronic materials, may be advantageous when employing
C–H activated direct arylation in certain circumstances.