Direct construction of polycyclic heterocycles from readily available compounds is one of the most important research areas in organic synthesis. Based on our recent findings, we investigated two types of tandem reactions. First, we studied tandem cyclization of bromoallenes, which can act as allylic dication equivalents, and found that the reaction of bromoallenes having a sulfamide moiety with NaOMe in MeOH in the presence of a palladium catalyst yields bicyclic compounds involving five- to eight-membered rings. In some cases, the tandem cyclization proceeds in the absence of a palladium catalyst. Second, we investigated the palladium(0)-catalyzed tandem cyclization of allenenes with various aryl halides and found that the reaction of allenenes with heteroaryl halides affords tri- or tetracyclic heteroarylic compounds in good yields.
