[CH2:1]=[C:2]1[CH2:8][CH:7](S(C2C=CC=CC=2)(=O)=O)[C:6]2[CH:18]=[C:19]([C:22]([O:24][CH3:25])=[O:23])[CH:20]=[CH:21][C:5]=2[O:4][CH2:3]1.P([O-])([O-])(O)=O.[Na+].[Na+].CO.O1CCCC1.O>[Na].[Hg].ClCCl>[CH2:1]=[C:2]1[CH2:8][CH2:7][C:6]2[CH:18]=[C:19]([C:22]([O:24][CH3:25])=[O:23])[CH:20]=[CH:21][C:5]=2[O:4][CH2:3]1728 mg (0.95 mmol) of 3% sodium amalgam are added portionwise at 0° C. to a suspension of 85 mg (0.23 mmol) of methyl 3-methylene-5-(phenylsulfonyl)-2,3,4,5-tetrahydro-1-benzoxepin-7-carboxylate, prepared according to example 1, and of 116 mg (0.95 mmol) of sodium hydrogenphosphate in 10 ml of a 1/1 methanol/tetrahydrofuran binary mixture. The reaction medium is subsequently stirred at ambient temperature for 4 hours. After addition of water and dichloromethane and filtering off the mercury, the phases are separated and the aqueous phase is extracted 3 times with dichloromethane. The combined organic phases are washed with a slightly acidic aqueous solution and then with brine. After drying and then concentrating under vacuum, 49 mg (98%) of methyl 3-methylene-2,3,4,5-tetrahydro-1-benzoxepin-7-carboxylate are obtained without additional purification in the form of an oil; 1H NMR (300 MHz, CDCl3): 2.53. (m, 2H), 2.93 (m, 2H), 3.89 (s, 3H), 4.49 (s, 2H), 5.0 (d, J=4.1 Hz, 2H), 7.0 (d, J=8.1 Hz, 1H), 7.86 (m, 2H).
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