A solution of 3.02 g (10.44 mmol) of [4-(5-Hydroxy-pent-1-ynyl)-phenyl]-methyl-carbamic acid tert-butyl ester in 70 ml CH2Cl2 was treated at 0° C. with 0.89 ml (11.48 mmol) methanesulfonylchloride, 1.26 ml (15.66 mmol) pyridine and 1.28 g (10.44 mmol) DMAP. The reaction mixture was warmed up over night to room temperature, water (10 ml) was added and the reaction mixture was stirred for 5 min. After extraction with aqueous 10% KHSO4/Et2O (3×) the organic phases were washed with aqueous KHCO3 (2×), aqueous 10% NaCl, dried (Na2SO4) and evaporated to yield 3.74 g (97%) of Methanesulfonic acid 5-[4-(tert-butoxycarbonyl-methyl-amino)-phenyl]-pent-4-ynyl ester, mp: 85-87° C.; MS: 367 (M).
