5-Bromobenzo[c][1,2,5]oxadiazole

5-Bromobenzo[c][1,2,5]oxadiazole, also known as 5-Bromo-2,1,3-benzoxadiazole, is a heterocyclic compound. It can be used as a pharmaceutical intermediate in drug synthesis. It is a derivative of benzo[c][1,2,5]oxadiazole which is a strong electron‐withdrawing unit compared to benzo[c][1,2,5]thiadiazole (BT). Hence BO is usually introduced as an acceptor to construct narrow band-gap donor-acceptor (D-A) materials[1]. BO is incorporated into the naphthalenediimide (NDI) based polymer backbone to improve the performance of polymer semiconductor.

Triphenylphosphine (1.1 mmol) was dissolved in dry toluene (3 mL) and stirred at 110°C under argon atmosphere; then 6-bromobenzo[c][1,2,5]oxadiazole 1-oxide (1 mmol) in toluene (0.5 mL) was added dropwise over 1 hour and the resulting mixture was stirred for 3 hours. After completion, the solvent was evaporated in vacuo, and the crude was purified through flash column chromatography (cyclohexane - diethyl ether 98:2) to afford 5-Bromobenzo[c][1,2,5]oxadiazole which is a pale pink solid.

[1] Song X, et al. Fusing Benzo[c][1,2,5]oxadiazole Unit with Thiophene for Constructing Wide-bandgap High-performance IDT-based Polymer Solar Cell Donor Material. Macromolecular Rapid Communications, 2018; 39: 1700782.