(1H-Indol-5-yl)boronic Acid (Powder) | CAS 144104-59-6 | ≥98%

Suzuki–Miyaura cross-coupling: (1H-Indol-5-yl)boronic acid is widely used as a nucleophilic coupling partner in palladium-catalysed Suzuki–Miyaura reactions to form carbon–carbon bonds between two aromatic or heteroaromatic rings. The boronic acid reacts with aryl or heteroaryl halides (bromides, chlorides, iodides) in the presence of a palladium catalyst and a base, producing biaryl or heteroaryl–indole products under mild conditions with broad functional group tolerance. The reaction is compatible with unprotected NH indole substrates, making it especially practical for late-stage diversification of complex molecules. This reagent has been employed in Suzuki–Miyaura couplings to construct aryl-hetarylfurocoumarins, aryl-substituted oxabenzindoles, and methanobenzindoles — polycyclic frameworks of interest in medicinal chemistry and natural product synthesis. Beyond traditional coupling with aryl halides, (1H-indol-5-yl)boronic acid is also compatible with aryl triflates, tosylates, and mesylates as electrophilic partners, expanding the range of accessible 5-substituted indole derivatives.

Medicinal chemistry and drug discovery: The indole scaffold is one of the most frequently encountered motifs in approved drugs and clinical candidates. (1H-Indol-5-yl)boronic acid provides direct access to 5-substituted indole derivatives, a substitution pattern found in compounds with diverse pharmacological profiles. It has been specifically used in the synthesis of indole-based inhibitors of MMP-13 (matrix metalloproteinase-13), a zinc-dependent enzyme involved in cartilage degradation that is actively investigated as a therapeutic target for osteoarthritis and degenerative joint diseases. This compound has also been utilised as a building block in the preparation of substituted pyrimidines that act as tubulin polymerisation inhibitors — compounds that disrupt microtubule assembly during cell division and are of significant interest in anticancer drug development programmes. The 5-position of the indole ring is the same substitution point present in serotonin (5-hydroxytryptamine), making 5-substituted indole derivatives particularly relevant to the development of serotonin receptor ligands for neurological and psychiatric research.

Rhodium-catalysed conjugate addition: (1H-Indol-5-yl)boronic acid serves as an aryl donor in rhodium-catalysed 1,4-conjugate addition reactions to unprotected maleimides, a class of cyclic electrophiles relevant to bioconjugation and the synthesis of succinimide-containing bioactive molecules. This reaction introduces the indole ring at the β-position of the maleimide carbonyl under mild transition-metal-catalysed conditions, providing 3-arylsuccinimide products in good yields (Tetrahedron Lett. 2007, 48, 4413). Rhodium-catalysed conjugate additions using heteroaryl boronic acids are valued for their high functional group tolerance, stereoselectivity, and compatibility with aqueous or protic solvent systems.

Oxidative cross-coupling and trifluoromethylation: This boronic acid participates in palladium- and copper-catalysed oxidative cross-coupling reactions with mercaptoacetylenes — terminal alkynes bearing a thiol group — to form carbon–carbon bonds between the indole ring and sulfur-containing alkyne fragments without requiring a pre-installed halide leaving group. (1H-Indol-5-yl)boronic acid and its pinacol ester derivatives are also documented substrates for copper-catalysed trifluoromethylation, a reaction that replaces the boronic acid group with a –CF₃ group. Trifluoromethylated indoles are of high interest in medicinal chemistry because the CF₃ group increases metabolic stability and lipophilicity of drug candidates, and in materials science for tuning the electronic properties of organic semiconductors. Kotovshchikov et al. (Molecules 2019, 24, 3523) provide a comprehensive review of indolylboronic acid preparation and applications including trifluoromethylation.

Materials science and organic electronics: Indole-containing building blocks are used in the construction of organic electronic materials, including hole-transport layers and emissive layers in organic light-emitting diodes (OLEDs). The electron-rich character of the indole nitrogen and the extended conjugation of the bicyclic system contribute to favourable charge-transport and light-emission properties. (1H-Indol-5-yl)boronic acid enables Suzuki–Miyaura coupling reactions that incorporate the indole unit into larger conjugated architectures designed for these applications. In polymer chemistry, 5-functionalised indole monomers derived from this boronic acid can be incorporated into conjugated copolymers through step-growth polycondensation, enabling systematic tuning of bandgap, HOMO/LUMO levels, and photophysical properties relevant to organic photovoltaics and fluorescence-based sensors.