Quest for "Innovative Discovery" by Organometalic Chemistry

　Organometalic chemistry is one of the fundamental research area with great potential; Innumerable combinations of elements and bonding modes are possible, and therefore, it still has a lot of room which has been still unexplored. In addition, development of organometalic chemistry enables to synthesize new compounds, which can lead to development of vairous fields including molecular catalysts, functional materials, polymer synthesis, and pharmaceuticals. Our research project is based on organic synthesis, but our goal is "innovative discovery" which would stimulate the related sciences.

1. Synthetic Transformations Exploiting Light as the Energy Source
　Photosynthesis produces carbohydrates starting from CO2 and H2O by exploiting solar light as the energy source. This intriguing synthetic system, if liberally interpreted, consists of two stages. One is "light reaction", a photo-induced reaction producing energetic compounds. Another is "dark reaction", a thermal reaction of the resulting energetic compounds. We are engaged in the development of new synthetic transformations of unreactive materials like CO2 based on this two-stage mechanism.

Selected References
(1) Angew. Chem., Int. Ed., 2012, 51, 11750. (2) Chem. Lett., 2013, 42, 1076. (3) Nature Commun., 2014, 5, 3188. (4) Angew. Chem., Int. Ed., 2015, 54, 7418. (5) J. Am. Chem. Soc., 2015, 137, 14063.

2. Synthetic Transformations Based on Cleavage of Unreactive Bonds
　 Reactivities of organic molecules generally originate from their π-bonds like C=C and C=O, polar σ-bonds like C–Br and C–Li, and non-bonding electron pairs. Non-polar σ-bonds like C–H and C–C are far less reactive, and thus remain intact under conventional reaction conditions in most cases. Therefore, if such non-polar σ-bonds are site-selectively cleaved and are utilized for construction of carbon skeletons, it would create unconventional opportunities of enormous synthetic potential. We have tackled to this challenging issue and found that transition metals like nickel and rhodium promote C-C cleavage reactions of cyclobutanones. In recent years, we have tried to exploit light as the driving force to induce even energetically uphill transformations, which are intrinsically difficult only by thermal reactions.

Selected References
(1) Nature, 1994, 370, 540. (2) J. Am. Chem. Soc. 1997, 119, 9307. (3) J. Am. Chem. Soc., 2002, 124, 13976. (4) J. Am. Chem. Soc., 2005, 127, 6932. (5) J. Am. Chem. Soc., 2007, 129, 12086. (6) J. Am. Chem. Soc., 2007, 129, 12596. (7) Angew. Chem., Int. Ed., 2012, 51, 2485. (8) J. Am. Chem. Soc., 2012, 134, 17502. (9) J. Am. Chem. Soc., 2014, 136, 5912. (10) J. Am. Chem. Soc., 2014, 136, 7217.

3. Multiple Functionailzation of Terminal Alkynes in One-pot
　Terminal Alkynes are readily available. In addition, they possess reasonable reactivity as well as stability. Consequently, terminal alkynes serve as useful starting substances for organic synthesis. We are engaged in the development of multiple functionalization of terminal alkynes to produce complex molecules in a single flask. For example, we have developed synthetic methods for N-heterocyclic compounds through denitrogenative transformations of triazoles robustly generated by the (3+2) cycloaddition reaction of terminal alkynes with azides (Huisgen reaction).

Selected References
[a] (1) J. Am. Chem. Soc., 2012, 134, 194. (2) J. Am. Chem. Soc., 2012, 134, 17440. (3) Angew. Chem., Int. Ed., 2013, 52, 3883. (4) J. Am. Chem. Soc., 2013, 135, 13652. (5) J. Am. Chem. Soc., 2014, 136, 2272. (6) J. Am. Chem. Soc., 2014, 136, 15905. (7) Angew. Chem., Int. Ed., 2015, 54, 9967. [b] (1) Angew. Chem., Int. Ed., 2011, 50, 11465. (2) J. Am. Chem. Soc., 2013, 135 11497. (3) J. Am. Chem. Soc., 2014, 136, 6223. (4) Angew. Chem., Int. Ed., 2015, 54, 12659.




革新的な発見を目指して

　有機金属化学は有機化学の得意とする結合の多様性と無機化学の得意とする元素の多様性を併せ持つ無限のポテンシャルを秘めた研究領域です。新しい化合物を生み出すことで分子触媒に、機能性材料に、精密高分子合成に、さらには新薬創製にと、次世代を切り開くパイオニアとしての役割を期待されています。私たちの研究室では有機化学を基盤技術としつつ、革新的な発見を目指して様々な研究テーマに取り組んでいます。

1. 光エネルギーを利用する有機合成
　光合成は太陽光のエネルギーを利用することで熱力学的に安定な水や二酸化炭素から糖類を作り出します。この興味深い合成システムは大きく分けると二段階で構成されています。すなわち、光エネルギーを利用して高エネルギー化合物を合成する明反応と、合成した高エネルギー化合物の熱反応である暗反応です。私たちはこの二段階の反応機構を有機合成に応用することで、光のエネルギーを利用して二酸化炭素などの安定な化合物を化学変換する手法の開発に取り組んでいます。

Selected References
(1) Angew. Chem., Int. Ed., 2012, 51, 11750. (2) Chem. Lett., 2013, 42, 1076. (3) Nature Commun., 2014, 5, 3188. (4) Angew. Chem., Int. Ed., 2015, 54, 7418. (5) J. Am. Chem. Soc., 2015, 137, 14063.

2. 不活性結合の切断に基づく有機合成
　一般に有機化合物の反応性のほとんどがアルケンやカルボニル基などのπ結合と、炭素—金属結合や炭素―ハロゲン結合などの極性σ結合、もしくは非共有電子対に起因します。一方、炭素—水素結合や炭素—炭素結合などの非極性σ結合は安定であり、反応性に乏しいことが知られています。このような非極性σ結合を触媒や反応剤を用いて活性化することは熱力学的にも速度論的にも困難ですが、逆に特定の非極性σ結合を選択的に活性化して、骨格の形成や官能基の導入に直截的に供することができれば、斬新な有機合成手法になり得ます。私たちは特に炭素－炭素結合の切断に取り組んでおり、これまでにロジウム触媒やニッケル触媒を用いて四員環骨格の炭素－炭素結合切断が起こることを見出しました。現在は主に光のエネルギーを利用することで歪みの小さい炭素－炭素結合を切断する合成手法の開発に取り組んでいます。

Selected References
(1) Nature, 1994, 370, 540. (2) J. Am. Chem. Soc. 1997, 119, 9307. (3) J. Am. Chem. Soc., 2002, 124, 13976. (4) J. Am. Chem. Soc., 2005, 127, 6932. (5) J. Am. Chem. Soc., 2007, 129, 12086. (6) J. Am. Chem. Soc., 2007, 129, 12596. (7) Angew. Chem., Int. Ed., 2012, 51, 2485. (8) J. Am. Chem. Soc., 2012, 134, 17502. (9) J. Am. Chem. Soc., 2014, 136, 5912. (10) J. Am. Chem. Soc., 2014, 136, 7217.

3. 末端アルキンを出発原料に利用するワンポット多官能基化
　末端アルキンは多様な誘導体を容易に入手できるうえ、適度な安定性と反応性を有しているため、有用な出発原料です。私たちは末端アルキンを出発原料として、１つのフラスコで複数の結合形成を行い、一気に複雑な化合物へと変換する反応の開発を行っています。例えば、末端アルキンとアジド化合物の(3+2)付加環化反応(Huisgen反応）によって効率良く生成するトリアゾールの脱窒素化反応を鍵反応として様々な含窒素化合物を合成する手法を開発しました。

Selected References
[a] (1) J. Am. Chem. Soc., 2012, 134, 194. (2) J. Am. Chem. Soc., 2012, 134, 17440. (3) Angew. Chem., Int. Ed., 2013, 52, 3883. (4) J. Am. Chem. Soc., 2013, 135, 13652. (5) J. Am. Chem. Soc., 2014, 136, 2272. (6) J. Am. Chem. Soc., 2014, 136, 15905. (7) Angew. Chem., Int. Ed., 2015, 54, 9967. [b] (1) Angew. Chem., Int. Ed., 2011, 50, 11465. (2) J. Am. Chem. Soc., 2013, 135 11497. (3) J. Am. Chem. Soc., 2014, 136, 6223. (4) Angew. Chem., Int. Ed., 2015, 54, 12659.