Practical Synthesis of Allyl, Allenyl, and Benzyl Boronates through S<sub>N</sub>1′-Type Borylation under Heterogeneous Gold Catalysis
Hiroki Miura, Yuka Hachiya, Hidenori Nishio, Yohei Fukuta, Tomoya Toyomasu, Kosa Kobayashi, Yosuke Masaki, Tetsuya Shishido
Abstract
Efficient borylation of sp3 C–O bonds by supported Au catalysts is described. Au nanoparticles supported on TiO2 showed high activity under mild conditions employing low catalyst loading conditions without the aid of any additives, such as phosphine and bases. A variety of allyl, propargyl, and benzyl substrates participated in the heterogeneously catalyzed reactions to furnish the corresponding allyl, allenyl, and benzyl boronates in high yields. Besides, Au/TiO2 was also effective for the direct borylation of allylic and benzylic alcohols. A mechanistic investigation based on a Hammett study and control experiments revealed that sp3 C–O bond borylation over supported Au catalysts proceeded through SN1′-type mechanism involving the formation of a carbocationic intermediate. The high activity, reusability, and environmental compatibility of the supported Au catalysts as well as the scalability of the reaction system enable the practical synthesis of valuable organoboron compounds.