A flask was charged under nitrogen with 3-bromo-5-nitro-benzoic acid (D5) (12.3 g, 50 mmol, 1 equiv), Cs2CO3 (24.4 g, 75 mmol, 1.5 equiv), tris(dibenzylideneacetone)dipalladium(0) (229 mg, 0.25 mmol, 0.005 equiv), Xantphos (433 mg, 0.75 mmol, 0.015 equiv) and dioxan (120 ml). 2-Pyrrolidin-2-one (5.7 ml, 75 mmol, 1.5 equiv) was then added via syringe and the resulting mixture was stirred at reflux for 60 h then cooled to room temperature and concentrated in vacuo. The residue was diluted with H2O and 1N aqueous NaOH solution and extracted twice with Et2O. The aqueous phase was then acidified to pH 1 and extracted three times with AcOEt. The combined organic phases were dried over MgSO4 and concentrated in vacuo to give 3-nitro-5-(2-oxo-pyrrolidin-1-yl)-benzoic acid (A27) (9.3 g, 75%) as a pale brown solid.
