Foreword

Molecular space chemistry is an important concept for the design of novel functional materials and catalysts. The research group “Creation of Molecular Space toward Innovative Transformations” was established by the members who advocate that the integration of supramolecular chemistry and catalytic chemistry enables flexible chemical conversion in multi-component molecular ensembles. Notably, most of the members have attained the position of full professor (or a similar position) within the past few years, which means that the members of this research group have been attracting attention in the field of state-of-the-art organic chemistry. To this volume of Chem. Pharm. Bull., four of the members, who have deep connections with the Pharamaceutical Society of Japan, contribute their cutting-edge results.

The first paper was coauthored by Prof. Naoya Kumagai, who received a Ph.D. degree from the Graduate School of Pharmaceutical Sciences, the University of Tokyo in 2005. He became a full professor at Keio University in 2021. His several papers published recently in Nature Communications have garnered the interest of many organic chemists. The title of his paper in this volume is “Oxygen-Fueled Iterative Hydride Transfer Driven by a Rigid Planar Architecture.” He describes an iterative hydride reduction/oxidation process promoted by a quasi-planar iminium cation rigidified by two concatenated quinoline units. The iminium proton was fixed by hydrogen bonding from neighboring quinoline nitrogen atoms, rendering the imine highly susceptible to hydride reduction. The thus-formed amine was readily oxidized by molecular oxygen to regenerate the quasi-planar iminium cation.

The second paper was coauthored by Prof. Seiji Shirakawa, who received a Ph.D. from Kyoto University in 2004. He has a diverse background and was a postdoctoral researcher in the Graduate School of Pharmaceutical Sciences, the University of Tokyo from 2005 to 2007. He established his own laboratory at Nagasaki University in 2014. He was a former representative of this group. His paper, titled “Chiral Bifunctional Selenide Catalysts for Asymmetric Iodolactonizations,” describes an enantioselective iodolactonization promoted by 1,1′-bi-2-naphthol (BINOL)-derived chiral bifunctional sulfide and selenide catalysts. In the asymmetric iodolactonization of 4-pentenoic acid, chiral bifunctional selenides showed good catalytic performances, whereas chiral sulfide catalysts unexpectedly gave nearly racemic products. Further investigation revealed that the importance of both a selenide moiety and hydroxy group being present on the chiral bifunctional selenide catalyst.

The third paper was coauthored by Prof. Takumi Furuta, who received a Ph.D. degree from the Graduate School of Pharmaceutical Sciences, Kyoto University in 1998. He became a full professor at Kyoto Pharmaceutical University in 2018. His recent paper on the one-pot synthesis of helicene compounds should be well remembered. His paper is titled “Syntheses, and Structural and Physical Properties of Axially Chiral Biaryl Dicarboxylic Acids Bearing Chalcogen Atoms” which describes the preparation and structural investigation of a series of axially chiral biaryl dicarboxylic acids bearing oxygen, sulfur and selenium atoms. The X-ray structure analysis revealed that the carboxy groups of these compounds are located in a co-planar geometry as a result of chalcogen-bonding interactions. Neutral bond orbital analysis revealed that not only chalcogen-bonding interactions but also the tetrel-bonding interaction contributed to the conformation control.

The fourth paper was coauthored by Dr. Yoshihiro Sohtome, who received a Ph.D. degree from the Graduate School of Pharmaceutical Sciences, the University of Tokyo in 2006, and has been a senior research scientist at RIKEN since 2018. His research area is quite broad, ranging from asymmetric synthesis to chemical biology. He is currently the representative of the “Creation of Molecular Space toward Innovative Transformations” group. The title of his paper in the volume is “Theoretical Insights into the Substrate-Dependent Diastereodivergence in (3 + 2) Cycloaddition of α-Keto Ester Enolates with Nitrones,” which describes computational analysis of their original (3 + 2) cycloaddition of Ni(II)-enolate with (E)-nitrone to provide a comprehensive analysis of how the bond-forming processes are regulated in the two-electron manifold in the triplet state. Molecular orbital analysis revealed a singly occupied molecular orbital–highest occupied molecular orbital (SOMO–HOMO) level inversion in the Ni(II)-enolate. In addition, distortion and interaction analysis revealed substrate-dependent diastereodivergence in the reaction when the structure of the nitrone was alternated.

The organizer believes that the “Creation of Molecular Space toward Innovative Transformations” group is certain to develop brilliant contributions in organic chemistry and sincerely appreciates the important contributions of all the authors.