2,3,5,6-Tetrabromo-4-methyl-4-nitro-2,5-cyclohexadien-1-one → 7-amino-9a-butyl-6-fluoro-4-nitro-1,2,9,9a-tetrahydro-3H-fluoren-3-one

A solution of 7-amino-9a-butyl-6-fluoro-1,2,9,9a-tetrahydro-3H-fluoren-3-one (34.6 mg, 0.126 mmol) in trifluoroacetic acid (0.25 mL) was treated with 2,3,5,6-tetrabromo-4-methyl-4-nitro-2,5-cyclohexadien-1-one (59 mg, 0.126 mmol). The resulting mixture was placed under a N2 atmosphere, sonicated briefly, and stirred at room temperature for one hour. The mixture was diluted with EtOAc (15 mL), washed successively with water, 5% NaHCO3 and brine, dried over MgSO4, filtered, and evaporated under vacuum to a brown oil (86 mg). The crude product was purified by preparative layer chromatography on a 0.1×20×20 cm silica gel GF plate, developing with 2:1 hexanes-EtOAc. The major UV visible band was eluted with 5% MeOH in CH2Cl2, the eluant was concentrated under vacuum to an orange oil (16 mg, 40%), and the oil was lyophilized from benzene to afford 7-amino-9a-butyl-6-fluoro-4-nitro-1,2,9,9a-tetrahydro-3H-fluoren-3-one as an amorphous solid.