Development and Fruits of Zinc Lewis Acid Catalysis: Serendipitous Emergence from Indium Catalysis

In 2008, while investigating an indium-catalyzed reaction, we encountered an experimental result serendipitously, which led to the development of the reaction that became the main subject of this account article. The finding eventually evolved into the discovery of the zinc/pyridine-catalyzed dehydrogenative N-silylation of indoles in a nitrile medium. The zinc/pyridine/nitrile system proved remarkably versatile, being applicable not only to the dehydrogenative C-silylation of indoles, but also to the dehydrogenative silylation, stannylation, and borylation of alkynes. This system is attractive in practice because all the catalyst, additive, and solvent are commercially available and thus executed in an easy manner. In addition, excellent functional-group tolerance with broad substrate scope and consistently high yields of products make this system valuable and reliable. Alkynyl-B(dan), derived from the dehydogenative borylation of alkynes, serves as a valuable platform for the synthesis of unsymmetrical tetrasubstituted alkenes. Moreover, we first achieved the Suzuki-Miyaura coupling (SMC) of alkynyl-B(dan) through the direct activation of the C-B(dan) bond, which has hitherto been recognized as highly robust and inert. Taking advantage of the insights, we further accomplished the first direct SMC of ArB(dan).