[C:1]([O:10][CH2:11][CH3:12])(=[O:9])[CH2:2][CH2:3][C:4]([O:6][CH2:7][CH3:8])=[O:5].[CH:13](OCC)=[O:14].[Na].O>C(OCC)C>[CH:13]([CH:2]([CH2:3][C:4]([O:6][CH2:7][CH3:8])=[O:5])[C:1]([O:10][CH2:11][CH3:12])=[O:9])=[O:14]A mixture of diethyl succinate (26.1 g, 25.0 mL, 0.150 mol) and ethyl formate (I1.1 g, 12.1 mL, 0.150 mol) was added drop wise over 1.5 hours to a stirred suspension of sodium (3.40 g, 0.150 mol) in diethyl ether (120 mL) at 0° C. under nitrogen. On completion of addition, stirring was continued at room temperature for 17 hours. Water (120 mL) was cautiously added to the resulting suspension and stirring continued until all the solids were dissolved. The layers were separated and the aqueous layer was washed with diethyl ether (100 mL). The aqueous layer was then acidified to pH 5 using 11 N HCl and extracted with diethyl ether (3×100 mL), the ethereal extracts of the acidified layer were combined, dried (Na2SO4) then evaporated to dryness under reduced pressure to give the title compound (I105) (16.5 g) as a yellow mobile liquid. The crude product was not purified further and was used directly in the following step.
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