3-Thienylboronic Acid | CAS 6165-69-1 | ≥98%

Suzuki–Miyaura cross-coupling: 3-Thienylboronic acid is a widely applied heteroarylboronic acid for palladium-catalysed Suzuki–Miyaura cross-coupling. The boronic acid at C3 reacts efficiently with aryl halides, heteroaryl halides, and vinyl halides under standard conditions to introduce the thiophen-3-yl unit into biaryl and heteroaryl frameworks in a single step. The 3-isomer is strongly preferred over the 2-isomer in synthetic practice — the C3 position avoids steric constraints adjacent to sulfur and shows significantly greater resistance to protodeboronation, making this the standard thienyl coupling partner for reliable, high-yielding Suzuki reactions. Applied in heteroaryl–heteroaryl coupling sequences with pyridines, pyrimidines, quinolines, and other five- and six-membered heterocyclic halides under nickel and palladium catalysis — compatible with a broad range of base/solvent systems including aqueous, microwave-assisted, and flow chemistry protocols.

Porphyrin synthesis and telomerase inhibition: Documented building block in the synthesis of thienyl-substituted porphyrins evaluated as telomerase inhibitors. Porphyrins are macrocyclic chromophores capable of intercalating into G-quadruplex DNA structures at telomere ends, stabilising them and inhibiting telomerase, an enzyme overexpressed in the majority of human cancer cells. The thiophen-3-yl group is introduced via Suzuki coupling onto the porphyrin periphery to modulate electronic properties, solubility, and G-quadruplex binding affinity. Thienyl-porphyrin conjugates prepared using this boronic acid represent a structurally distinct class of antiproliferative agents with a mechanism of action — telomerase inhibition — that is independent of conventional cytotoxic drug mechanisms, making them of interest for overcoming multidrug resistance in cancer research programmes.

1,4-Disubstituted imidazole synthesis and antibacterial research: Applied in the synthesis of 1,4-disubstituted imidazoles bearing the thiophen-3-yl group as potential antibacterial agents. The imidazole scaffold is a privileged heterocycle in antibacterial drug discovery, and 1,4-disubstituted variants with thienyl substituents have been evaluated for activity against both Gram-positive and Gram-negative bacterial strains. The boronic acid provides direct Suzuki coupling access to the 4-(thiophen-3-yl)imidazole motif without requiring pre-functionalised thienyl starting materials.

β-Lactamase inhibition and efflux pump research: 3-Thienylboronic acid is itself a direct inhibitor of AmpC β-lactamase (Ki = 22.1 ± 3.5 μM), one of the key resistance enzymes that hydrolyse β-lactam antibiotics. It has also been shown to potentiate ciprofloxacin activity by 4-fold at concentrations of 8–16 μg/mL against Staphylococcus aureus 1199B overexpressing the NorA multidrug efflux pump, representing one of the first boronic acid compounds identified as a novel NorA efflux pump inhibitor. Fontaine et al. (J. Med. Chem. 2014, 57, 2536).

Conductive polymers and organic electronics: Applied as a monomer in the enzymatic and electrochemical polymerisation of conductive poly(3-thienylboronic acid) (PTBA) films. The resulting conductive polymer combines the electronic conductivity and optical properties of the polythiophene backbone with the reversible diol-binding capability of the pendant boronic acid groups, enabling dual-function materials for electrochemical biosensors, glucose-responsive electrodes, and enzymatic biofuel cells. Huang et al. (Biosens. Bioelectron. 2013, 44, 41) demonstrated HRP-catalysed polymerisation of PTBA for high-performance mono- and bi-enzyme amperometric biosensing. Also used in the construction of π-conjugated thiophene-containing oligomers and polymers via Suzuki polycondensation — the thiophen-3-yl unit contributes to HOMO–LUMO gap tuning and charge-carrier mobility, with applications in organic field-effect transistors (OFETs), organic photovoltaics (OPVs), and electrochromic devices. The 3-substitution pattern promotes more planar backbone conformation relative to 2-substituted thiophene couplings, favouring π–π stacking and improved charge transport in thin-film devices.

Glycated haemoglobin (HbA1c) biosensing: Thiophene-3-boronic acid self-assembled monolayers (SAMs) on gold electrodes have been used for the selective electrochemical detection of glycated haemoglobin (HbA1c), the primary clinical biomarker for long-term blood glucose monitoring in diabetes management. The boronic acid residues on the SAM surface selectively bind the glycosylated sites of HbA1c via reversible boronate ester formation, enabling label-free impedimetric detection with high selectivity over non-glycated haemoglobin. Park et al. (Anal. Chem. 2008, 80, 8035).

Medicinal chemistry and boronate ester chemistry: The thiophene ring is one of the most prevalent heterocycles in approved drugs across cardiovascular, CNS, haematology, and anti-infective therapeutic areas, making this boronic acid a high-value entry point for the introduction of the thienyl pharmacophore into drug discovery programmes. Applied in the preparation of thiophen-3-yl pinacol and MIDA boronate esters as bench-stable masked boronic acid equivalents for iterative cross-coupling and automated synthesis workflows.