[CH2:1]([N:8]1[C:12]([C:13]([O:15][CH3:16])=[O:14])=[C:11]([OH:17])[C:10]([OH:18])=[C:9]1[C:19]([O:21][CH3:22])=[O:20])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.Br[CH2:24][CH2:25]Br.C(=O)([O-])[O-].[K+].[K+]>CN(C=O)C>[CH3:22][O:21][C:19]([C:9]1[N:8]([CH2:1][C:2]2[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=2)[C:12]([C:13]([O:15][CH3:16])=[O:14])=[C:11]2[O:17][CH2:24][CH2:25][O:18][C:10]=12)=[O:20]A mixture of dimethyl N-benzyl-3,4-dihydroxypyrrole-2,5-dicarboxylate (0.1 mol), 1,2-dibromoethane (0.1 mol), and potassium carbonate (0.5 mol) in dry DMF was stirred for 12 h under argon at 105-110° C. After cooling to 25° C., the reaction mixture was poured onto ice-water. The crude product was collected by suction filtration and purified by recrystallization in methanol yielding 6-benzyl-2,3-dihydro-6H-[1,4]dioxino[2,3-c]pyrrole-5,7-dicarboxylic acid dimethyl ester as colourless crystals in 55-65% yield.
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