A solution of KOH 50% (3 ml) is added to an equimolar solution of 3-(3-methylbut -2-enyloxy)-4-acetylxanthen-9-one (2.4 g, 0.0075 mol) and benzaldehyde (0.8 g, 0.0075 mol) in ethanol 95%; the addition is performed under energetic stirring at room temperature. The reaction is left under stirring for one night and then diluted with water and acidified; the precipitate is separated by filtration and dried under vacuum. The compound is crystallized by methanol to give 2.1 g of product m.p. 116-118° C., 1H-NMR (CDCl3)δ:1.69 (s, 3H); 1.72 (s, 3H); 4.71 (d, 2H, J=6.5); 5.38-5.40 (m, 1H); 7.05-7.10 (m, 2H); 7.08 (d, 1H, J=8.8 Hz); 7.10 (d, 1H, J=16 Hz); 7.30-7.48 (m, 6H); 7.50-7.58 (m, 2H); 7.65-7.60 (m, 1 H) 8.30-8.33(m, 1H); 8.42 (d, 1H, J=8.9 Hz).
