Prof. Takayoshi Arai (director of the Soft Molecular Activation Research Center and the Chiba Iodine Resource Innovation Center) and specially appointed Assistant Prof. Satoru Kuwano (Molecular Chirality Research Center) of the Chiba University Graduate School of Science, Faculty of Science, have succededed in "developing π electron compound activation functions using a halogen bond-donor iodine catalyst" (Figure 1). This study was the result of joint research with Prof. Masahiro Yamanaka of the Rikkyo University Department of Chemistry.
Figure 1: Synthesis of indole derivatives based on activation of π electron system compounds using a halogen bond-donor iodine catalyst
Study background and objective
Figure 2. [4+2] cycloaddition reaction using a halogen bond-donor iodine catalyst
Figure 3: Comparison of iodine catalyst and Brønsted acid catalyst
Figure 4: Analysis of transition states mediated by CI···π halogen bonds
Social contributions, ramifications
The results were published in Angewandte Chemie International Edition, a top chemistry journal.
Kuwano, S.; Suzuki, T.; Yamanaka, M.; Tsutsumi, R.; Arai, T. Angew. Chem. Int.Ed., [10.1002/ange.201904689].
This study was funded by the following grant-in-aids for scientific research: basic research (B) JP19H02709, young researchers 19K15553, and research in new academic fields JP16H01004 and JP18H04237 (precision controlled reactions) and JP18H04660 (hybrid catalysts). Assistance was also provided by the Futaba Foundation.
Explanation of terms
Halogen bonds have attracted attention as a novel interaction with clear directionality that have applications in catalytic chemistry and the creation of functional molecules. However, because halogen bonds are formed by the positive charge on the back side of the RX bond of the molecular framework, it has been difficult to achieve stereoselectivity and other forms of high-level structural recognition.
In alkenes, alkynes, and aromatic compounds, in addition to the σ bond that forms the molecular framework, π electrons are used to form unsaturated bonds (also called π bonds). The π bond is higher in energy than the σ bond and determines the attributes (physical properties) of the molecule. An accurate understanding of π electrons is essential to understanding the reactivity of substrates. Recently, the functions of molecules with a large number of conjugated π electrons has attracted attention.
Indoles possess the structure shown at right and are common in biologically active natural products. Creating new methods of synthesizing molecules with indole skeletons is important for the development of new drugs.
Chemical reactions in which a π electron system is reacted with another π electron system (addition) to form a ring is called a cycloaddition reaction. These reactions are classified according to the number of backbone atoms of the molecule involved in the reaction. The example to the right is the famous Diels-Alder reaction, in which the number of backbone atoms is 4 for butadiene and 2 for ethylene, and is thus described as a "[4+2] cycloaddition reaction."
Soft Molecular Activation Research Center
Chiba Iodine Resource Innovation Center
Feb 28, 2020