A solution of 5,6-dimethoxy-indanone (19 g, 0.10 mol) in methanol (8 mL) is stirred under inert
atmosphere at room temperature. Slowly add NaOH flakes
(12.8 g, 0.32 mol) followed by N-benzyl-piperidine-4-carboxaldehyde (20.2 g, 0.10 mol) to the reaction mixture. The
mixture was stirred at room temperature for 3 h and progress
of the reaction was monitored by TLC (hexane:ethyl acetate;
1:1). Once the reaction is complete, the solid formed was
filtered, washed with 5 % acetic acid and then with methanol
and dried. The obtained solid (34 g) was taken into a round
bottom flask and refluxed with DMF (50 mL). Gradually cooled
to room temperature and stirred for 2 h, filtered the solid
formed, wash with chilled methanol to afford a pale yellow
crystalline solid 1-Benzyl-4-(5,6-dimethoxy-1-oxoindan-2-ylindenemethyl)piperidine (32.0 g, 84 %); m.p.: 175-177 °C.
