to room temperature the precipitate is filtered off with suction and washed with a little ethyl acetate and diethyl ether for the purification the solid is recrystallized from acetic anhydride and chromatographed over silica gel solvent u2014 dichloromethane the yield is 54 of a pale yellow powder having a melting point gt 300 u00b0 c further purification is carried out by sublimation a solution of 2 50 g 10 mmol of 2 7 diacetylfluorene in 12 65 g 80 mmol of butyric anhydride is added dropwise at a temperature of 60 u00b0 c over 3 hours to a mixture of 7 52 g 40 mmol of a boron trifluoride acetic acid complex and 12 65 g 80 mmol of butyric anhydride while stirring the reaction mixture is stirred for a further 8 hours at 60 u00b0 c after cooling to room temperature the precipitate is filtered off with suction and washed with a little ethyl acetate and diethyl ether for the purification the solid is recrystallized from acetic anhydride and chromatographed over silica gel solvent u2014 dichloromethane the yield is 66 of a yellow powder having a melting point gt 300 u00b0 c further purification is carried out by sublimation a solution of 2 64 g 10 mmol of 2 7 diacetyl 9 10 dihydronaphthene in 12 65 g 80 mmol of butyric anhydride is added dropwise at a temperature of 60 u00b0 c over 3 hours to a mixture of 7 52 g 40 mmol of a boron trifluoride acetic acid complex and 12 65.