General procedure for the synthesis of 1-(5-bromo-2-thienyl)-2,2-dihydroxyacetophenone from 2-acetyl-5-bromothiophene: A mixture of selenium dioxide (8.66 g, 78 mmol), water (2.8 mL), and 1,4-dioxane (75 mL) was heated to reflux until all the solids were completely dissolved (about 15 min). Subsequently, 2-acetyl-5-bromothiophene (8 g, 39 mmol) was added to the reaction system in batches. The reaction mixture was continued to be stirred under reflux conditions for 15 h. Then, it was cooled to room temperature, filtered through a diatomaceous earth pad (1.5 in. x 3 in. dia.) and the filter cake was washed well with ether. The filtrate was concentrated under reduced pressure to give a yellow residue. Kugelrohr distillation (150°C/1 Torr) was carried out on this residue, which was collected to give glyoxal as a yellow oil and immediately added to boiling water. By recrystallization from water, filtration and drying at 37°C and 5 Torr, 1-(5-bromo-2-thienyl)-2,2-dihydroxyacetophenone hydrate was finally obtained as white to pink acicular crystals (6.723 g, 73% yield). The structure of the product was determined by 1H NMR (300 MHz, DMSO-d6) δ 5.43 (t, J = 6.1 Hz, 1H), 6.93 (d, J = 6.1 Hz, 2H), 7.37 (d, J = 4.1 Hz, 1H), 7.81 (d, J = 4.1 Hz, 1H) and 13C NMR (300 MHz, DMSO-d6) δ 90.28, 122.32, 132.23, 135.73, 141.15, 189.6 were confirmed.
