Sodium hydride → 6-(tetrahydropyran-2-yloxymethyl)-4-(2-triisopropylsilanyloxyethyl)-4H-benzo[1,4]oxazin-3-one

The solution of 5.50 g of 6-(tetrahydropyran-2-yloxymethyl)-4H-benzo[1,4]oxazin-3-one and 100 ml of N,N-dimethylformamide-tetrahydrofuran (1:1) is cooled to 0° C., admixed with 0.800 g of sodium hydride dispersion (60%) and stirred over 30 minutes. The mixture is admixed with 7.90 g of (2-iodoethoxy)triisopropylsilane and stirred at room temperature for a further 16 hours. The reaction mixture is poured onto ice-water (150 ml) and extracted with ethyl acetate (3×150 ml). The organic phases are washed successively with aqueous sodium hydrogencarbonate solution (1×100 ml), water (100 ml) and brine (100 ml), dried over sodium sulphate, filtered and concentrated by evaporation. The title compound is obtained as a colourless oil from the residue by means of flash chromatography (SiO2 60F). Rf=0.57 (1:1 EtOAc-heptane); Rt=6.71.