A mixture of (3S,5R,6R,7S)-6-(4-fluorophenyl)-3-(2-methoxy-5-(2-(trifluoromethyl)imidazol-1-yl)phenyl)-1-oxaspiro[4.4]nonane-7-carboxylic acid (40 mg, 0.079 mmol), diphenylphosphoryl azide (24 mg, 0.08 mmol), and diisopropylethylamine (0.017 mL, 0.095 mmol) in toluene was stirred at RT for 0.5 h, and then heated at 100° C. for 50 min. After addition of benzyl alcohol (0.5 mL), the mixture was heated at 100° C. overnight. Upon cooling to RT, the mixture was taken up in 25 mL of ethyl acetate and washed successively with 15 mL of saturated aqueous sodium bicarbonate and 15 mL of brine. Drying over sodium sulfate and evaporation afforded the crude product, which was purified by column chromatography, eluting with 3-5% ethyl acetate in dichloromethane, to give the title compound (30 mg, 62%) as a light brown syrup. Mass spectrum (NH3/CI): m/z=610.1 (M+1).
