An Unexpected FeCl3-Catalyzed Cascade Reaction of Indoles and o-Hydroxychalcones for the Assembly of Chromane-Bridged Polycyclic Indoles.

An unexpected FeCl3-catalyzed cascade reaction of simple indoles and o-hydroxychalcone was reported, leading to densely functionalized and strained chromane-bridged polycyclic indoles in moderate to good yields. This reaction not only establishes a new transformation of indoles and o-hydroxychalcones but also provides an efficient method for the synthesis of structurally complex and congested chromane-bridged polycyclic indoles.