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 3, 4, 5-trimethoxy-benzaldehyde (1.47 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 2.2 g of product m.p. 153-55° C., 1H NMR (CDCl3) δ:1.69 (s, 3H); 1.72 (s, 3H); 3.85-3.91 (m, 9H); 4.73 (d, 2H, J=6.5); 5.38-5.40 (m, 1H); 6.78 (s, 2H); 7.03 (d, 1H, J=16 Hz); 7.09 (d, 1H, J=8.8 Hz); 7.23-7.42 (m, 2H); 7.27 (d, 1H J=16 Hz); 7.80-7.87; (m, 1H); 8.32 (d, 1H, J=8.8 Hz); 8.44 (d, 1H, J=8.9 Hz).
