To a stirred solution of 1-[2,4-bis(benzyloxy)-6-(4-nitrophenoxy)phenyl]-N-hydroxyethanimine (10 g, 44 mmol) was added drop wise 2 M n-ButLi in hexane (45 mL, 44 mmol) at −78° C. and the stirring was continued for 1 hour at −78° C. then for ½ hour at room temperature. After recooling at −78° C., a solution of diethyl oxalate (3.22 g, 22 mmol) in THF (50 mL) was cannuled into the cloudy solution. The mixture was warmed at rt over 16 hours before the addition of a NH4Cl saturated solution (100 mL). The organic and aqueous layers were separated and the latter was diluted with ethyl acetate and thoroughly washed with brine. After drying over Na2SO4, the solvent was removed and the residue was chromatographed on silica gel eluting with ethyl acetate/hexane 7/5, to provide the title compound (2.7 g, yield 17%).
