tert-Butyl 4-{[4-(2-butynyloxy)phenyl]sulfonyl}-1,4-diazepane-5-carboxylate (0.425 g, 0.96 mmol) in dichloromethane at 25° C. (10 mL) was treated with triethylamine (0.28 mL, 2.02 mmol) followed by benzoyl chloride (0.12 mL, 1.06 mmol) and dimethylaminopyridine (10 mg). After 18 hours aqueous workup gave tert-butyl 1-benzoyl-4-{[4-(2-butynyloxy)phenyl]sulfonyl}-1,4-diazepane-5-carboxylate. 1H NMR (dmso-d6, 300 MHz): 1.24 (s, 9H, t-bu), 1.82 (s, 3H, CH3), 2.0-4.0 (m, 8H, CH2), 4.65 (s, 1H, CH), 4.85 (s, 2H, CH2), 7.0-7.9 (m, 9H, ArH). Treatment with trifluoroacetic acid (4 mL) in dichloromethane (10 mL) for 6 hours gave, after concentration in vacuo followed by chromatography on silica gel eluting with dichloromethane/methanol, 1-benzoyl-4-{[4-(2-butynyloxy)phenyl]sulfonyl}-1,4-diazepane-5-carboxylic acid as a foam (0.328 g).
