Enantiomerically pure aryl and benzyl glycidyl ethers undergo stereospecific cyclizations leading to 3-chromanols or to tetrahydrobenzo[c]oxepin-4-ols under mild conditions in the presence of a catalytic amount of FeBr3/3AgOTf. The same processes are also mediated, albeit in a much less efficient manner, by AuCl3/3AgOTf. The set of active mediators in this group of processes (BF3·Et2O, FeBr3, FeBr3/3AgOTf, AuCl3/3AgOTf) shows its nature as Friedel-Crafts reactions and disfavors the intermediacy of arylgold species.
