4-Toluenesulfonyl chloride → (1R,2R)-4-(tert-Butyl-dimethyl-silanyloxy)-2-(toluene-4-sulfonyloxymethyl)-cyclopentanecarboxylic acid ethyl ester

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To a cold (0° C.) solution of (1R,2R)-4-(tert-Butyl-dimethyl-silanyloxy)-2-hydroxymethyl-cyclopentanecarboxylic acid ethyl ester (example 68 step 4, 500 mg) and triethyl amine (836 mg) in dichloromethane (5 mL) was added toluene-4-sulfonyl chloride (1.53 g). The reaction mixture was stirred overnight at room temperature then partitioned between hydrochloric acid (1N) and dichloromethane. The aqueous layers was extracted with dichloromethane and the combined organic layers were washed with half saturated aqueous solution of sodium hydrogenocarbonate and brine, then dried over sodium sulfate, filtered and concentrated in vacuo. The residue was purified by flash chromatography on silica gel with a gradient of cyclohexane/ethyl acetate (1:0 to 19:1 v/v) as eluant to afford the title compound (602 mg, 80%) as a yellow liquid.

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