Sodium hydride → 8-Methoxy-3,4-dihydro-2H-pyrido[2',3':4,5]pyrrolo[2,1-b][1,3]oxazine

Under an inert atmosphere, 160 mg (4 mmol) of sodium hydride (60% in oil) are added slowly at 0° C. to a solution of 380 mg (1.34 mmol) of the compound obtained in Step E in 10 ml of N,N-dimethylformamide. The reaction mixture is stirred at 0° C. for 30 minutes before being hydrolysed with ice and then extracted with ethyl acetate. The organic phase is washed several times with water, dried over magnesium sulphate, concentrated and purified by flash chromatography over silica gel (eluant: ethyl acetate/petroleum ether, 95:5) to yield the title compound in the form of a brown solid.