Structural insights into the TES/TFA reduction of differently substituted benzofurans: dihydrobenzofurans or bibenzyls?

Various polysubstituted benzofurans were reduced by using triethylsilane in trifluoracetic acid. 2,3-Dihydrobenzofurans or bibenzyl compounds were obtained in high yields, depending on the nature of the substituents at C2 and on the benzene ring of the core structure. A p -anisole substituent at C2 of benzofurans always led to the corresponding bibenzyls.