Efficient Indium-Catalyzed C—H Functionalization/Silylation of Heteroarenes

摘要

As a consequence of their unique chemical, physical, and biological properties, silyl-substituted arenes have attracted wide interest from the synthetic material science, and pharmaceutical sectors. Traditionally, silyl substituents have been introduced by the addition of aryl lithium or magnesium reagents to silicon electrophiles, and this method often necessitates the use of protecting groups. Consequently, transition-metal-catalyzed cross couplings of aryl halides with disilanes or hydrosilanes have grown in popularity, especially if base- or nucleophile-sensitive functional groups are present. More recently, direct C—H functionalization has emerged as a conceptually and economically attractive alternative for the direct silylation of arenes. However, challenges remain and the general utility of this strategy is restricted in many instances by 1) poor regioselectivity, 2) stringent structural requirements, 3) noncommercial/ expensive reagents, 4) harsh reaction conditions (typically 120-200 °C), and 5) impractical ratios of arene to the silicon reagent (10:1-60:1). Herein, we report an efficient, regioselective protocol for the bipyridine-ligated, iridium-catalyzed C—H functionalization/silyation of a wide variety of heteroarenes under comparatively mild conditions. Importantly, the reaction does not require protection of the N—H groups and uses only a small excess (3 equiv) of the inexpensive triethylsilane [Eq. (1)].