Metal-Free Approach to Biaryls from Phenols and Aryl Sulfoxides by Temporarily Sulfur-Tethered Regioselective C–H/C–H Coupling

We have developed metal-free regiocontrolled
dehydrogenative C–H/C–H
cross-coupling of aryl sulfoxides with phenols by means of trifluoroacetic
anhydride. Because the reaction would proceed through an interrupted
Pummerer reaction followed by sulfonium-tethered [3,3]-sigmatropic
rearrangement, the C–H/C–H coupling takes place exclusively
between the ortho positions of both substrates. Various
functional groups including carbonyl, halo, siloxy, and even boryl
moieties are compatible. The biaryl products naturally possess hydroxy
and sulfanyl groups, which allows the products to be useful synthetic
intermediates, as evidenced by the syntheses of π-expanded heteroarenes
such as unprecedented 7,12-dioxa[8]­helicene.