Efficient Iridium‐Catalyzed CH Functionalization/Silylation of Heteroarenes

Abstract

As a consequence of their unique chemical, physical and biological properties, silyl-substituted arenes have attracted wide interest from the synthetic,[1] material science,[2] and pharmaceutical sectors.[3] Traditionally, silyl substituents have been introduced via addition of aryl lithium or magnesium reagents to silicon electrophiles, although this often necessitates the use of protecting groups.[4] Consequently, transition metal catalyzed cross couplings of aryl halides with disilanes or hydrosilanes have grown in popularity, especially if base-or nucleophile-sensitive functionality are present.[5] More recently, direct C-H functionalization[6] has emerged as a conceptually and economically attractive alternative for the direct silylation of arenes. It is evident, however, that challenges remain and the general utility of this strategy is restricted in many instances by, inter alia, (1) poor regioselectivity, (2) stringent structural requirements, (3) noncommercial/expensive reagents, (4) harsh reaction conditions (typically 120°–200°C), and/or (5) impractical ratios of arene to silicon reagent (10:1 to 60:1).[7–9] Herein, we report an efficient, regioselective protocol for the bipyridine-ligated, iridium-catalyzed[9] C-H functionalization/silyation of a wide variety of heteroarenes under comparatively mild conditions. Importantly, the reaction does not require protection of N-H groups and uses only a small excess (3 equiv) of inexpensive triethylsilane (eq 1).