Quinolin-5-ylboronic Acid CAS 355386-94-6 | ≥97%

Suzuki–Miyaura Cross-Coupling and the 5-Quinolyl Fragment

Quinolin-5-ylboronic acid enables direct palladium-catalysed Suzuki–Miyaura cross-coupling to install the 5-quinolyl fragment onto aryl, heteroaryl, and vinyl halides (Miyaura & Suzuki, Chem. Rev. 1995, 95, 2457). Quinoline is one of the most privileged heterocyclic scaffolds in medicinal and materials chemistry. The 5-position is the peri position relative to the ring-junction nitrogen, meaning the nitrogen lone pair is oriented directly toward the C-5 substituent across the ring fusion. This spatial relationship influences the dihedral angle, conformational preference, and intramolecular electronic interactions of the resulting 5-arylquinoline product. The compound couples efficiently under standard Suzuki conditions (Pd(PPh₃)₄ or Pd(dppf)Cl₂, K₂CO₃, dioxane/water) and is also compatible with nickel-catalysed protocols.

Heterocyclic Building Block for SAR Campaigns

Quinolin-5-ylboronic acid is used in the construction of 5-arylquinoline and bis(heterocyclic) scaffolds for structure–activity relationship studies. The 5-quinolyl motif provides a rigid, planar nitrogen-containing biaryl framework capable of hydrogen bonding — a key interaction in medicinal chemistry lead optimisation. The quinoline nitrogen enhances water solubility and hydrogen-bonding capacity relative to naphthalene, making 5-quinolyl a preferred bioisostere for naphthyl and other fused carbocyclic aromatic fragments in research compounds.

OLED Materials and Coordination Chemistry

Quinoline is the foundational heterocycle in the archetypal OLED emitter tris(8-hydroxyquinolinato)aluminium (Alq₃), first demonstrated as an electroluminescent material by Tang and VanSlyke (Appl. Phys. Lett. 1987, 51, 913). 5-Substituted quinoline derivatives prepared via Suzuki coupling serve as electron-transport and hole-blocking materials in multilayer OLED architectures. The quinoline nitrogen's electron-accepting character lowers the LUMO energy of the resulting biaryl, enhancing electron injection from the cathode. The nitrogen donor in 5-arylquinoline products also enables coordination to transition metals (Ir, Pt, Ru, Zn), producing luminescent metal complexes for phosphorescent OLED emitters and ditopic bridging ligands for porous metal–organic framework (MOF) construction.

Fluorescent Probes and Chemical Sensors

The quinoline fluorophore provides intrinsic UV/visible fluorescence with a large Stokes shift — values exceeding 150 nm have been reported for quinoline-based probes (Liu et al., Talanta 2019, 192, 6). 5-Substituted quinoline derivatives exhibit tuneable emission wavelengths depending on the electronic character of the C-5 substituent introduced via Suzuki coupling. The quinoline nitrogen acts as a proton-responsive switch — protonation shifts the absorption and emission wavelengths, enabling ratiometric pH measurement across the physiological range (Hande et al., ChemBioChem 2020, 21, 1492). This built-in pH sensitivity is a distinctive advantage of quinoline-based sensors over carbocyclic fluorophores, with applications in biological imaging, environmental monitoring, and metal cation detection (Zn²⁺, Cu²⁺, Fe³⁺).