Sulfurane [S(IV)]-Mediated Fusion of Benzynes Leads to Helical Dibenzofurans

Here
we disclose a sulfurane-mediated method for the formation
of dimeric dibenzofuran helicenes via the reaction between diaryl
sulfoxides and hexadehydro-Diels–Alder (HDDA) derived benzynes.
A variety of S-shaped and U-shaped helicenes were formed under thermal
conditions. Both experimental and DFT studies support a sulfur­(IV)-based
coupling (aka ligand coupling) mechanism involving tetracarbo-ligated
S­(IV) intermediates undergoing reductive elimination to afford the
helicene products. This process involves the de novo generation of
five new rings in a single operation and constitutes a new method
for the construction of topologically interesting, polycyclic aromatic
compounds.