[K].[O-]CCCC.[C:7]([CH2:11][O:12][C:13]1[CH:18]=[CH:17][CH:16]=[CH:15][C:14]=1[O:19][CH2:20][C:21]([O:23][CH3:24])=[O:22])(OC)=[O:8].C(O)(=O)C>CS(C)=O.O>[O:8]=[C:7]1[CH2:11][O:12][C:13]2[CH:18]=[CH:17][CH:16]=[CH:15][C:14]=2[O:19][CH:20]1[C:21]([O:23][CH3:24])=[O:22]Potassium t.-butoxide (15.8 g.) dissolved in DMSO (130 ml.) is added dropwise over a 45 minute period to 1,2-bis-carbomethoxymethoxybenzene (18.3 g.) in DMSO (30 ml.) under an atmosphere of nitrogen. The mixture then is stirred 3 hours at ambient temperature and a mixture of acetic acid (16 ml.) and water (200 ml.) is added. The reaction mixture is extracted with benzene, the powdery material removed by filtration and the benzene then dried over magnesium sulfate and the benzene then evaporated leaving 3-oxo-4-carbomethoxy-3,4-dihydro-2H-1,5-benzodioxepin that is used in the following step without purification.
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