To a suspension of 1.18 g (2.64 mmol) of 3(R)-amino-1,3,4,5-tetrahydro-1-[[2'-(1H-tetrazol-5-yl)[1,1'-biphenyl]-4-yl]methyl]-2H-1-benzazepin-2-one, hydrochloride (Example 4, Step C) in 30 mL of methylene chloride under nitrogen at -15° C. was added 0.923 mL (2.64 mmol) of triethylamine followed by 0.294 mL (2.64 mmol) of 3,3-dimethylacryloyl chloride. The reaction mixture was stirred at -15° C. for 2 hours then quenched by the addition of 1N hydrochloric acid. The mixture was diluted with 50 mL of methylene chloride and washed with 50 mL of 1N hydrochloric acid and brine. The organic layer was removed and concentrated to dryness under vacuum. The residue was redissolved in 30 mL of methanol and treated with 1.5 mL of 9N hydrochloric acid. After stirring for 30 minutes, the mixture was concentrated to dryness under vacuum to give 1.3 g (2.63 mmol, 99%) of the product as a white solid.
