N12CCCN=C1CCCCC2.[O:12]=[C:13]1[CH2:19][CH:18](S(C2C=CC=CC=2)(=O)=O)[C:17]2[CH:29]=[C:30]([C:33]([O:35][CH3:36])=[O:34])[CH:31]=[CH:32][C:16]=2[O:15][CH2:14]1.O.Cl>ClCCl>[O:12]=[C:13]1[CH:19]=[CH:18][C:17]2[CH:29]=[C:30]([C:33]([O:35][CH3:36])=[O:34])[CH:31]=[CH:32][C:16]=2[O:15][CH2:14]10.084 ml (1.05 equivalents) of 1,8-diazabicyclo[5.4.0]undec-7-ene is added at ambient temperature to 217 mg (0.6 mmol) of methyl 3-oxo-5-(phenylsulfonyl)-2,3,4,5-tetrahydro-1-benzoxepin-7-carboxylate, prepared according to example 2, in suspension in 20 ml of dichloromethane. From the addition of the base, the medium becomes translucent and slightly yellow. After addition of water and 1N hydrochloric acid, the phases are separated by settling and then the aqueous phase is extracted three times with dichloromethane. The combined organic phases are washed with a saturated sodium hydrogencarbonate solution and then with brine. After drying and then concentrating under vacuum, 90 mg (68%) of methyl 3-oxo-2,3-dihydro-1-benzoxepin-7-carboxylate are obtained in the form of a white solid; M.p.=89–93° C.
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