Metal-mediated cyclization of aryl and benzyl glycidyl ethers: A complete scenario

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.