General procedure for the synthesis of 2-amino-5-bromo-2'-chlorobenzophenone from o-chlorobenzoyl chloride and 4-bromoaniline:
1. o-Chlorobenzoyl chloride (177 mL, 1.4 mol) was cooled to 0°C in an ice-water bath in a 2L flask equipped with a condenser and thermometer.
2. 4-Bromoaniline (100 g, 0.58 mol) was added to the cooled solution.
3. The mixture was heated to 120 °C and held at this temperature for 1 hour until complete consumption of 4-bromoaniline was confirmed by TLC analysis (Expanding Agent: EtOAc:Hexane = 1:4).
4. The solution was heated to 160 °C and anhydrous ZnCl2 (95 g, 0.70 mol, pre-flame-dried) was added all at once.
5. Increase the temperature to 195 °C and stir at this temperature for 3 hours until no more bubbles are produced.
6. cooled the mixture to 120 °C and slowly added 12% HCl aqueous solution (350 mL) dropwise.
7. After maintaining reflux for 20 minutes, pour off the aqueous layer. Repeat this process 4 times.
8. Add water (350mL), keep refluxing for 20 minutes and pour out the water. Repeat until solids are no longer lumpy.
9. Add 72% H2SO4 (700mL) to the residue and heat and reflux for approximately 1 hour until the reaction mixture becomes a homogeneous dark colored solution.
10. The hot acidic solution was poured into the ice-water mixture with stirring, and the resulting precipitate was filtered and washed with plenty of cold water until the pH of the solid was about 6.
11. the solid was suspended in ice water, 40% aqueous NaOH solution (290 mL) was carefully added, stirred for 2 hours and the solid was filtered and washed with ice water.
12. Suspend the solid again in ice water, adjust dropwise with 40% H2SO4 to pH ≈ 3, filter the remaining solid and wash with water to neutral.
13. The yellow solid product (66.1 g, 37.0% yield) was dried and used in the next step without further purification.
Product characterization: 1H NMR (300MHz, CDCl3) δ 6.49 (s, br, 2H), 6.65 (d, 1H, J=8.82Hz), 7.26-7.8 (m, 6H).
