To a solution of (2-chloro-4-methoxy-phenyl)-acetic acid (CAS Reg. No. 91367-09-8) (20 g, 100 mmol) in tetrahydrofuran (400 ml) were added N,N-dimethylformamide (1 ml) and oxalylchloride (20.2 g, 160 mmol) dropwise (15 min). The mixture was stirred overnight at room temperature. The solvent was evaporated; toluene was added and again evaporated. The residue was dried under high vacuum to give the crude acid chloride. To a cooled solution (ice bath) of 4-methyl-2H-1,4-benzoxazin-3(4H)-one (16.6 g, 100 mmol) in 1,2-dichloroethane (110 ml) was added AlCl3 (39.9 g, 300 mmol). The mixture was stirred for 30 min and a solution of the acid chloride in 1,2-dichloroethane (110 ml) was added dropwise during 1.2 h at 2° C. The mixture was stirred at 0° C. for 4.5 h. The mixture was poured into ice water and hydrochloric acid and extracted three times with dichloromethane. The organic phases were dried (MgSO4), filtered and concentrated. The residue was dried under high vacuum for 17 h. The solid product was stirred with ethanol (180 ml) for 1.5 h at r.t., filtered off and dried under high vacuum to give the title compound (26.1 g) as an off-white solid. MS (m/e)=346.1 [M+H+].
