One of the most important missions of chemists is to maximize the latent properties of the elements located in the third and subsequent lows of the periodic table, and to construct a new world of molecular chemistry. Among them, Dr. Toshiaki Murai focused on compounds with C=S, C=Se, C=Te, P=S, and P=Se groups, which were considered difficult to synthesize, established a new reaction system to synthesize novel derivatives with these unsaturated bonds, elucidated the delocalization of the electrons in conjugated systems containing heavier main group elements, and finally created a new concept concerning them. Furthermore, he discovered new molecular transformations that could only proceed with unsaturated bonds containing heavier main group elements and pioneered an important field that would have a ripple effect in a wide range of chemical societies. The details of his major achievements are shown below.

1. Development of carboxylic acid isologues containing C=Se and C=Te groups
Carboxylic acids and their derivatives, esters and amides, are ubiquitous organic compounds existing everywhere in nature. The basic skeleton of these compounds has a C=O group. Derivatives in which this C=O group is replaced with a C=S group have been widely known for a long time. On the other hand, the derivatives substituted with C=Se group and C=Te groups, were almost unexplored. In this regards, Dr. Murai succeeded in synthesizing isologues, in which two oxygen atoms of carboxylates were replaced with a sulfur atom and a selenium atom, or two selenium atoms for the first time. The acid ammonium salts were stable even at room temperature under inert atmosphere, while the acids themselves were highly labile even at low temperatures. He also established a new synthetic pathway for tellurium isologues of amides, i.e., telluroamides from ordinary amides. The methylation of telluroamides led to the telluroiminium salts. The structures in solutions and in the solid states of the salts were disclosed by NMR spectroscopy and X-ray structural analyses. In combination of these results with molecular orbital calculations, the fundamental notion of the delocalization of electrons in the system with unsaturated bonds including selenium and tellurium atoms was provided.

2. Development of Sequential Reaction with C=S Group as Key Species: Multicomponent Coupling Reaction
Dr. Murai discovered that sulfur isologues of amides and esters, i.e., thioamides and thioesters, in which a C=S group is present, exhibit unique nucleophilicity and electrophilicity which were not observed for amides and esters, fully utilized those properties, and established unprecedented carbon-carbon bond-forming reactions. When two different carbon nucleophiles were added to thioformamides, they were successively incorporated to the carbon atom of the C=S group along with the elimination of the sulfur atom to selectively give tertiary amines. Furthermore, in the case of thioformates, nucleophiles were introduced to the carbon and sulfur atoms of the C=S group to generate carbanions in the system. Further addition of an electrophile to the solution has also proceeded. In other words, four component coupling reactions starting from thioformates with two carbon nucleophiles and one electrophile were achieved. Reactions of secondary thioamides with BuLi generate carbanions adjacent to the nitrogen atom, and various electrophiles, including alkyl halides, carbonyl compounds, and oxiranes, were selectively incorporated into the carbanion centers.

3. Development of 5-Aminothiazole: Application to Fluorescent Materials
Dr. Murai fully utilized the new reactions using thioformamides and thioamides presented above and created fluorescent compounds with unique skeletons and made these compounds express various functionalities. He succeeded in synthesizing 5-N-arylaminothiazoles via the reaction of nitrogen-adjacent carbanions with thioformamides. The resulting 5-N-arylaminothiazoles showed blue fluorescence emission in spite of the twisted structures of the thiazole ring and the arylamino group at the 5-position. Furthermore, by selecting the combination of aryl groups and arylamino groups incorporated into the thiazole ring, various emission colors from blue to red can be expressed. Vapochromism, in which the color changes with the vapor of halogenated solvents, halochromism, and mechanochromism, in which the emission color changes with the addition of acid or stress, were also discovered. This also enabled white light emission in the solid state and in a solution.

4. Development of New Reactions with P=S and P=Se Groups as Key Species
In response to large number of reports on the use of phosphoric acid with a binaphthyl group as asymmetric Brønsted acid catalysts, Dr. Murai focused on a series of compounds in which the oxygen atom of phosphoric acids was replaced with a sulfur or selenium atom and found unprecedented transformations. While carrying out the research on the synthesis of acids in which the oxygen atoms of phosphoric acid were replaced with sulfur and selenium atoms, he discovered that phosphoroselenoyl chlorides, with a binaphthyl group were synthesized with high efficiency. This unprecedented and stable chlorides readily reacted with oxygen, nitrogen, and carbon nucleophiles under basic conditions, and the selective substitution reaction took place at the phosphorus atom. In addition, selenoyl chlorides could be used for the kinetic resolution of alcohols and the desymmetrization of meso-alcohols. Unprecedented compounds derived from phosphoroselenoyl chlorides also reacted with carbon and heteroatom nucleophiles, which provided new reactions and the successful synthetic methods for phosphate derivatives. In particular, he discovered the reaction via the transfer of the axial chirality of the binaphthyl group to the central chirality of the phosphorus atom for the first time. The substitution reaction at the phosphorus atom of the resulting compounds also proceeded with high selectivity to provide new reactions system leading to the formation of a range of P-chirogenic optically active compounds including drug candidates.

As described above, Dr. Murai utilized unsaturated bonds containing heavier main group elements by his own methods, and by novel molecular design and skillful synthetic methods, and created new reactions and new compounds. Chemistry of heavier main group elements is a field of a treasure trove of new reactions and new compounds that can provide new functions and properties for the creation of new materials, and transcending the boundaries of conventional organic and inorganic chemistry. These achievements are interesting and significant as they provided important chemical knowledges for the advancement of research in related fields. Therefore, his achievements were recognized as worthy of the Chemical Society of Japan Award.