A mixture of (3S,4S)-6-(4-tert-butyldimethylsilyloxyphenyl)sulphonyl-3,4-dihydro-3,4-epoxy-2,2,3-trimethyl-2H-benzo[b]pyran (0.71 g) (see Preparation 14), 1,2-dihydro-4-hydroxy-2-methyl-1-oxophthalazine (0.846 g) (see Preparation 21), pyridine (0.4 ml) and 1,4-dioxane (10 ml) was heated under reflux for 4 days. The solvent was removed under reduced pressure, the residue was dissolved in ethyl acetate and washed first with dilute aqueous citric acid solution and then with brine. The organic phase was dried (anhydrous magnesium sulphate), the solvent was removed and the crude product was chromatographed on silica eluting with a solvent gradient of 100:1:0.15 to 180:20:1 dichloromethane: methanol: 35% aqueous ammonia solution to yield (3S,4R)-3,4-dihydro-4-(1,2-dihydro-2-methyl-1-oxophthalazin-4-yl)oxy-3-hydroxy-6-(4-hydroxyphenyl)sulphonyl-2,2,3-trimethyl-2H-benzo[b]pyran (0.12 g) as a solid.
