4-Indolylboronic acid pinacol ester is an organoboron compound featuring an indole ring system protected by a pinacol ester group. This structural motif makes it a stable and versatile building block, commonly referred to as 4-indoleboronic acid pinacol ester or 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-indole. Its primary application is in organic synthesis, particularly in transition-metal-catalyzed cross-coupling reactions such as the Suzuki-Miyaura reaction. The boronic ester functionality allows for the efficient introduction of the 4-indolyl moiety into more complex molecular architectures. This makes it a valuable intermediate in medicinal chemistry for the synthesis of drug candidates and biologically active molecules that contain the indole scaffold, a privileged structure found in many pharmaceuticals. As a protected boronic acid derivative, it offers improved stability and handling compared to the free boronic acid, facilitating its use in multi-step synthetic sequences. It is a standard reagent available from major chemical suppliers for research and development purposes.