To a solution of ethyl chloroformate (293 mg, 2.7 mmol) in THF (1.5 mL) was added a solution of cis-3-benzyl-6-bromo-8-methyl-2,3,4,4a,9,9a-hexahydro-1H-3-aza-fluorene (320 mg, 0.90 mmol) in dry THF (1.5 mL) dropwise over 10 min at 0° C. The reaction mixture was warmed to 20° C., stirred for 15 h and concentrated in vacuo. The residue was chromatographed in silica gel column (Hex/EtOAc 7/3) to yield cis-6-bromo-8-methyl-1,2,4,4a,9,9a-hexahydro-3-aza-fluorene-3-carboxylic acid ethyl ester (130 mg, 0.38 mmol).
