A mixture of 5-((3-hydroxy-4-methoxyanilino)methylene)-2,2-dimethyl-1,3-dioxane-4,6-dione (20 g, 69 mmol), potassium carbonate (12.4 g, 90 mmol) and benzyl bromide (15.4 g, 90 mmol) in DMF (100 ml) was heated at 65° C. for 2 hours. Two thirds of the DMF was removed from the mixture by evaporation, the mixture was diluted with water, adjusted to pH4 with 5M hydrochloric acid and extracted with ethyl acetate. The combined extracts were washed with water and then brine, dried (MgSO4) and the volatiles removed by evaporation. The solid residue was triturated with ether, and collected by filtration and dried under vacuum to give 5-((3-benzyloxy-4-methoxyanilino)methylene)-2,2-dimethyl-1,3-dioxane-4,6-dione (22 g, 83%) as a cream solid.
