A three-necked round-bottomed flask was equipped with a stir bar and condenser. Chloroform (25 mL) and acetic acid (25 mL) were added to the reaction flask, then 1,2,4,5-tetra(thiophen-2-yl)benzene (0.830g, 2 mmol, 1 eq.) and N-bromosuccinimide (1.817g, 10 mmol, 5 eq.) were added. The reaction was heated at 75°C for 17 hours in air. Reaction completion was monitored by ¹H NMR of an aliquot every two hours. Upon completion of the reaction, the flask was cooled to room temperature and more chloroform was added until all the solid had dissolved. The organic layer was washed with saturated sodium bisulfite solution (2 x 200 mL) and saturated potassium carbonate solution (2 x 200 mL). The organic layer was dried over sodium sulfate, filtered, and concentrated under reduced pressure on a rotary evaporator. The product was recrystallized from 25% ethyl acetate in hexanes to yield a green-brown powder (1.079 g, 1.49 mmol, 75% yield).

Acetic acid greatly accelerates this reaction. Brominating in chloroform yielded little to no product. The reaction was generally done in five hours, but did not overbrominate if left over the weekend. 
Please note: NBS must be recrystallized from water before being used in order to receive the best results. 
NMR analysis: an aliquot was removed, dried on a hot air gun, and NMR was taken in CDCl₃, specifically to monitor for the loss of the thienyl proton in the 5 position. 
The authors thank Dr. Daniel Ralston for DART MS collection.

The authors thank the NSF REU program at James Madison University for funding (CHE 1757874).

¹H NMR (400 MHz, CDCl₃): δ 7.501 (s, 2H), 6.964 (d, 4H, J = 3.6 Hz), 6.744 (d, 4H, J = 3.6 Hz) 

¹³C NMR (400MHz, CDCl3): δ 141.607, 133.408, 133.264, 127.426, 127.047, 126.361.

Mass Spec: Calculated: 722.1780 g/mol; observed: 722.6476 g/mol.