Copper-Catalyzed Diboration of Ketones: Facile Synthesis of Tertiary α-Hydroxyboronate Esters

The diboration of ketones with the (ICy)CuOt-Bu catalyst was developed to provide access to tertiary α-hydroxyboronate esters. The (ICy)CuOt-Bu catalyst was generated in situ with (ICy)CuCl and NaOt-Bu to afford a more efficient catalyst than the preformed (ICy)CuOt-Bu. These conditions result in the diboration of various ketones in toluene at 50 °C in 2−22 h. Treatment of the resulting products with silica gel affords the corresponding α-hydroxyboronate esters.