Association of Halogen Bonding and Hydrogen Bonding in Metal Acetate-Catalyzed Asymmetric Halolactonization

• Published in: iScience 2019-02, Vol.12, p.280-292
• Main Authors: Arai, Takayoshi, Horigane, Kodai, Watanabe, Ohji, Kakino, Junki, Sugiyama, Noriyuki, Makino, Hiroki, Kamei, Yuto, Yabe, Shinnosuke, Yamanaka, Masahiro
• Format: Article
• Language: English
• ISSN: 2589-0042; 2589-0042
• DOI: 10.1016/j.isci.2019.01.029

Cooperative activation using halogen bonding and hydrogen bonding works in metal-catalyzed asymmetric halolactonization. The Zn (OAc) -3,3'-bis(aminoimino)binaphthoxide (tri-Zn) complex catalyzes both asymmetric iodolactonization and bromolactonization. Carboxylic acid substrates are converted to zinc carboxylates on the tri-Zn complex, and the N-halosuccinimide (N-bromosuccinimide [NBS] or N-iodosuccinimide [NIS]) is activated by hydrogen bonding with the diamine unit of chiral ligand. Halolactonization is significantly enhanced by the addition of catalytic I . Density functional theory calculations revealed that a catalytic amount of I mediates the alkene portion of the substrates and NIS to realize highly enantioselective iodolactonization. The tri-Zn catalyst activates both sides of the carboxylic acid and alkene moiety, so that asymmetric five-membered iodolactonization of prochiral diallyl acetic acids proceeded to afford the chiral γ-butyrolactones. In the total description of the catalytic cycle, iodolactonization using the NIS-I complex proceeds with the regeneration of I , which enables the catalytic use of I . The actual iodination reagent is I and not NIS.