[C:1]([C:3]([O:5][CH2:6][CH2:7][CH2:8][CH3:9])=[O:4])#[N:2].C1(N=[CH:17][C:18]2[O:19][CH:20]=[CH:21][C:22]=2[CH3:23])C=CC=CC=1.ClC(OCCCC)=O>C1(C)C(C)=CC=CC=1>[CH2:6]([O:5][C:3]([C:1]1[CH:23]=[C:22]2[CH:21]=[CH:20][O:19][C:18]2=[CH:17][N:2]=1)=[O:4])[CH2:7][CH2:8][CH3:9]n-Butyl cyanoformate(13.7 g, 0.108 mol) and 3-methylfuran-2-carbaldehyde-N-phenylimine(5.0 g, 27.0 mmol) were mixed at room temperature in xylene (25 mL) then heated to reflux at 120 to 140° C. with stirring. A xylene (15 mL) solution of 7.40 g (54.2 mol) of n-butyl chloroformate was added dropwise for an hour to the resulting mixture. After all the solution had been added, the reaction mixture was heated to reflux for 2 hours, it was allowed to cool to room temperature, and the solvent was distilled off to give 7.10 g of crude product. This product was purified by column chromatography on silica gel, giving 2.71 g (45.8% yield) of 5-n-butoxycarbonylfuro[2,3-c]pyridine.
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