C=O.C(O[C:8]([N:10]1[CH2:15][CH2:14][CH:13]([CH2:16][O:17][C:18]2[CH:28]=[CH:27][C:21]([C:22]([O:24][CH2:25][CH3:26])=[O:23])=[CH:20][C:19]=2[O:29][CH3:30])[CH2:12][CH2:11]1)=O)(C)(C)C.Cl.CCOCC>C(O)=O>[CH3:30][O:29][C:19]1[CH:20]=[C:21]([CH:27]=[CH:28][C:18]=1[O:17][CH2:16][CH:13]1[CH2:12][CH2:11][N:10]([CH3:8])[CH2:15][CH2:14]1)[C:22]([O:24][CH2:25][CH3:26])=[O:23]
Formaldehyde (12M, 37% in water, 35 ml, 420 mmol) was added to a solution of ethyl 4-(1-(tert-butoxycarbonyl)piperidin-4-ylmethoxy)-3-methoxybenzoate (35 g, 89 mmol) in formic acid (35 ml). After stirring at 95° C. for 3 hours, the volatiles were removed by evaporation. The residue was dissolved in methylene chloride and 3M hydrogen chloride in ether (40 ml, 120 mmol) was added. After dilution with ether, the mixture was triturated until a solid was formed. The solid was collected by filtration, washed with ether and dried under vacuum overnight at 50° C. to give ethyl 3-methoxy-4-(1-methylpiperidin-4-ylmethoxy)benzoate (30.6 g, quant.).
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