Rh/Cu-cocatalyzed Ring-opening Diborylation of Dibenzothiophenes for Aromatic Metamorphosis via Diborylbiaryls

Here, we report a new method for aromatic metamorphosis of dibenzothiophenes into other cyclic skeletons via 2,2'-diborylbiaryls. In the presence of bis(pinacolato)diboron and cesium fluoride, the two C-S bonds of dibenzothiophenes underwent a couple of sequential borylation reactions cocatalyzed by rhodium and copper complexes to afford the corresponding 2,2'-diborylbiaryls. As a proof-of-principle, 2,2'-diborylbiphenyl was converted into a series of extended p-systems such as fulvenes, dibenzofuran, oxaborin, and azaborin.