The condensation of 5,6-dimethoxy-1-indanone (I) with 1-benzylpiperidine-4-carboxaldehyde (II) by means of butyllithium and diisopropylamine in THF gives 1-benzyl-4-(5,6-dimethoxy-1-oxoindan-2-ylidenemethyl)piperidine (III), which is reduced with H2 over Pd/C in THF and treated with HCl in dichloromethane - ethyl acetate.
11C-Labeled donepezil was prepared by methylation of 2-(1-benzylpiperidin-4-ylmethyl)-6-hydroxy-5-methoxyindan-1-one (I) with 11CH3I by means of tetrabutylammonium hydroxide in DMF.