Raloxifene → 4'-tert-Butyldimethylsilyl-6-hydroxy Raloxifene

A solution was prepared consisting of 10 g (21.1 mmol) of [2-(4-hydroxyphenyl)-6-hydroxybenzo[b]thien-3-yl][4-[2-(1-piperidinyl)ethoxy]phenyl]methanone and 6 g (49.1 mmol) of dimethylaminopyridine in 700 mL of THF-DMF (6:1)(v/v). This solution was stirred for one hour at ambient temperature and then cooled to 0° C. in an ice bath. To this solution was added 2.9 g (19.3 mmol) of tert-butyl-dimethylsilylchloride. The reaction mixture was stirred under a nitrogen atmosphere and allowed to warm to ambient temperature. After seventy-two hours, the reaction was quenched with the addition of a saturated solution of aqueous NH4Cl. The organic layer was separated and washed with water, brine, and finally dried by filtration through anhydrous Na2SO4 and evaporated to dryness. The crude product was triturated with CH2Cl2, allowed to stand for three hours, and filtered to remove unreacted starting material. This resulting product is a mixture of isomers, which are separated by chromatography on a silica gel column eluted with a linear gradient beginning with CHCl3 and ending with CHCl3 --MeOH (19:1)(v/v). The desired fractions were determined by tlc, combined, and evaporated to dryness. This yielded 5.1 g of the title compound, isolated as a yellow crystalline solid.