Lewis-acid-mediated ring-exchange reaction of dihydrobenzofurans and its application to the formal total synthesis of (−)-quinocarcinamide

An unusual Lewis-acid-mediated ring-exchange reaction of dihydrobenzofurans is described. The fused tricyclic ring system is the key structural element for this reaction as it restricts C–N bond rotation and/or destabilizes the benzofuran ring. We achieved the formal total synthesis of (−)-quinocarcinamide using a combination of this reaction and the Au(I)-catalyzed 6-endo-dig hydroamination of an alkyne