To a solution of 2-(2′,4′-dichloro-4-ethylbiphenyl-3-yl)-4,4,6,6-tetramethyl-1,5-dioxaspiro[2.4]heptan-7-one (0.0418 g, 0.10 mmol) in toluene (0.3 ml) is added p-toluenesulfonic acid monohydrate (0.019 g, 0.10 mmol). The mixture is then heated at 150° C. for 1 hour, after which it is allowed to cool to room temperature. The reaction mixture is poured into distilled water, dried over sodium sulfate, then concentrated in vacuo to afford 4-(2′,4′-dichloro-4-ethylbiphenyl-3-yl)-2,2,6,6-tetramethylpyran-3,5-dione.
