To a solution of 30 g (58.8 mmol) of 6-hydroxy-2-(4-hydroxyphenyl)benzo[b]thiophen-3-yl 4-[2-(1-piperidinyl)ethoxy]phenyl ketone hydrochloride in 120 mL of anhydrous THF and 60 mL of anhydrous DMF was added 20 mL (144 mmol) of anhydrous triethylamine and 9.75 g (64.7 mmol) of tertbutyldimethylsilyl chloride under a nitrogen atmosphere. The reaction mixture was heated at 60° C. in an oil bath for 4 h and then cooled to room temperature. The solution was diluted with 225 mL of toluene, filtered through a medium glass frit, and concentrated at reduced pressure. The residue was purified by PrepLC (0 to 4% MeOH in CH2Cl2) to give 6.77 g (11.5 mmol, 20%) of a yellow foam.
