To a solution of 4-[3-chloro-4-(methylsulfonyl)phenyl]-5-[(2R,3R,7R)-2,3-diphenyl-1,4-dioxaspiro[4.4]non-7-yl]pent-1-en-3-one (525 mg) in ethanol (3 mL) were added 5-[(tetrahydro-2H-pyran-2-yloxy)methyl]-1,3-thiazole-2-carbaldehyde (259 mg), 3-benzyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazol-3-ium chloride (28.3 mg) and triethylamine (57 μL), and the mixture was stirred with heating under reflux for 1.5 hr. After cooling to room temperature, the reaction mixture was diluted with ethyl acetate and washed with water. The ethyl acetate layer was dried (MgSO4) and concentrated. The residue was subjected to silica gel column chromatography, and the title compound (416 mg, yield 56%) was obtained as a pale-yellow amorphous solid from a fraction eluted with ethyl acetate-hexane (1:1, volume ratio).
