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.

Nickel-catalyzed reductive carboxylation reactions of aryl electrophiles typically require the use of metallic reducing agents. At present, the prevailing perception is that these serve as both a source of electrons and as sources of Lewis acids that may aid CO2 insertion into the Ni-C bond. Herein, we provide evidence for the in situ formation of organometallic species from the metallic reductant, a step that has either been ruled out or has been unexplored in catalytic carboxylation reactions with metal powder reductants. Specifically, we demonstrate that Zn(0) acts as a reductant and that Zn(II) generates arylzinc species that might play a role in the C(sp 2)-S carboxylation of arylsulfonium salts. Overall, the reductive Ni-catalyzed C(sp 2)-S carboxylation reaction proceeds under mild conditions in a non-amide solvent, displays a wide substrate scope, and can be applied to a formal para C-H carboxylation of arenes.

A regioselective C-H sulfanylation of aryl sulfoxides with alkyl aryl sulfides in the presence of acid anhydride was developed, which resulted in the formation of 1,4-disulfanylarenes after dealkylation of initially formed sulfonium salts. The reaction began with Pummerer-type activation of aryl sulfoxides followed by nucleophilic attack of alkyl aryl sulfides. The nucleophilic attack occurred exclusively at the para positions, or at specific positions in case the para position was not available, under perfect control by the dominating sulfoxide directors regardless of any other substituents. The initially formed aryl sulfonium salts were isolable and usefully served as aryl halide surrogates for palladium-catalyzed arylation with sodium tetraarylborates.

A series of dihetero[8]helicene have been systematically synthesized in enantiomerically enriched forms by utilizing the characteristic transformations of organosulfur functionality. The synthetic route begins with assembling a ternaphthyl common synthetic...