p-Methylsulfonylbenzaldehyde (1.5 g) is added to a solution of methyl 5-dimethylamino-2-methyl-3-indenylacetate (2.5 g) from Example 3 Part B in 1,2-dimethoxyethane (1.5 ml) at 0° C. followed by the addition of potassium t-butoxide (1.1 g). The reaction mixture is kept in the ice-bath for 4 hours and at room temperature for 18 hours. The mixture is diluted with ether (15 ml), and the potassium salt is filtered off. The salt is dissolved in 30 ml of water and neutralized with dilute hydrochloric acid to pH 6-6.5. The crude acid precipitates, is collected by filtration and is recrystallized to give pure (Z)-1-(p-methylsulfonylbenzylidene)-5-dimethylamino-2-methyl-3-indenylacetic acid.
