Toward the Development of New Organic Reactions

Takuya Kochi (Associate Professor, Department of Chemistry)

We primarily research the development of new organic reactions. Organic compounds, from pharmaceuticals to functional materials, play various important roles in our daily lives. On the other hand, if you look at a university-level organic chemistry textbook, you will notice that while there are descriptions of these resulting organic compounds, a very large portion is dedicated to "reactions." This is because one of the great attractions of organic chemistry is the ability to "synthesize" organic molecules with complex structures by first designing them yourself and then using reactions based on rational thinking. In other words, reactions are important tools for synthesizing various organic compounds, and by skillfully combining a variety of reactions, we can construct the target compounds.

With many reactions already known, the question may arise as to whether it is necessary to develop even more. In reality, the development of organic reactions is still being vigorously pursued by a great number of researchers worldwide, and many new reactions are being discovered daily. This is because further development is essential for synthetic organic chemistry. Of course, it is also important to efficiently synthesize already known pharmaceuticals, natural organic compounds, and functional materials. However, humanity dreams of discovering organic molecules that surpass the functions of existing substances or possess functions that existing substances do not have, and is attempting to synthesize countless organic compounds around the world. While there are a great many known organic compounds that already exist in the world (tens of millions?), there are so many organic compounds that have not yet been created that one can relatively quickly arrive at an unknown substance simply by drawing a random organic molecular structure. And, of course, no one knows the properties or functions of these unknown substances. Therefore, there is a demand for methods that can rapidly supply a large number of organic compounds (designed for specific purposes, of course), preferably with as little burden on society as possible and at a low cost. The development of new organic reactions, which forms the foundation for this, is of great importance.

We are attempting to develop new organic reactions mainly by using compounds called complexes, which contain transition metal elements, as catalysts. The use of transition metal complex catalysts in organic reactions is now commonplace, as evidenced by the fact that research in this field has already been the subject of the Nobel Prize in Chemistry three times this century. The appeal of using transition metal complexes in organic reactions lies in their diverse reaction modes and unique selectivity. For example, they make it possible to achieve bond formations, cleavages, and rearrangements that are normally difficult, and to selectively induce only the desired reaction. The actual reaction that occurs varies depending on the chosen conditions. For us, the periodic table is a toolbox of "elements" with various properties. From this, we can realize unprecedented organic reactions by first appropriately selecting an element to place at the catalytic active center, then choosing from a variety of structures for the "ligand," which is a group of atoms placed on the element, and finally devising reaction conditions from various angles. For example, we recently developed an unprecedented bond-construction method by skillfully incorporating a mechanism called "chain walking," in which a palladium catalyst moves along a carbon chain, into an organic reaction. The results were featured in Keio Research Highlights on the Keio University website. We are currently conducting research aimed at developing further new reactions using this method.

Thus far, I have discussed the development of new organic reactions. Reaction development proceeds by making full use of various substances such as elements and compounds, but in reality, there are still many aspects of the properties of these substances that are not yet understood. For example, although the rapid progress of chemistry has increased our understanding of the reactivity of each transition element when it has a certain ligand, the current situation is that the actual reactivity is not something we can easily predict. Conversely, by further deepening our fundamental understanding of the properties of these various elements, we can expect to develop new reactions that will lead to dramatic advances in chemistry if we can draw out the "individuality" of elements never seen before. We also hope to continue our research by earnestly engaging with various compounds, aiming to contribute to such organic reactions.