[Synthesis of hypervalent organo-λ(3)-bromanes and their reactions by using leaving group ability of λ(3)-bromanyl group].

Hypervalent organo-λ(3)-iodanes have attracted great interest in organic synthesis; however, the chemistry of hypervalent organo-λ(3)-bromanes remains largely unexplored, mainly because of synthetic difficulties. Iodobenzene is readily oxidized by common oxidants such as peracids under mild conditions, whereas bromobenzene is inert. Since the ionization potential of bromobenzene (8.98 eV) is higher than that of iodobenzene (8.69 eV), hypervalent-λ(3)-bromane would show much higher reactivity. We overcame this problem by using difluoro(aryl)-λ(3)-bromane (Frohn's reagent), which serves as a pivotal progenitor of various λ(3)-bromanes including imino-λ(3)-bromane, cyclopent-1-enyl-λ(3)-bromane, (E)-β-alkylvinyl-λ(3)-bromane, and diacetoxy-λ(3)-bromane. These reagents possess highly unusual reactivity based on the enormously enhanced nucleofugality of the aryl-λ(3)-bromanyl group.