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A solution of 25.0 g (53.2 mmol) of 1-[4-(4-fluorophenoxy)benzenesulfonylamino]-cyclopentanecarboxylic acid benzyl ester and 10.8 mL (106 mmol, 2 equivalents) of ethyl propiolate in 200 mL of dry tetrahydrofuran at 1° C. was treated with 53.2 mL (53.2 mmol, 1 equivalent) of a solution of tetrabutylammonium fluoride in tetrahydrofuran (1M) over 45 minutes. The resulting solution was allowed to warm slowly to ambient temperature and stirred overnight. The tetrahydrofuran was displaced with toluene at reduced pressure, and the toluene solution was washed with water and brine, diluted to 600 mL with toluene, stirred with 90 g of silica gel for three hours, filtered, and concentrated to 25.14 g (83%) of 1-{(2-ethoxycarbonylvinyl)-[4-(4-fluorophenoxy)benzenesulfonyl]amino}-cyclopentanecarboxylic acid benzyl ester as an orange oil. 1H NMR (CDCl3) indicated a 1.5:1 trans/cis ratio.

1. washthe toluene solution was washed with water and brine
2. additiondiluted to 600 mL with toluene
3. stirringstirred with 90 g of silica gel for three hours
4. filtrationfiltered
5. concentrationconcentrated to 25.14 g (83%) of 1-{(2-ethoxycarbonylvinyl)-[4-(4-fluorophenoxy)benzenesulfonyl]amino}-cyclopentanecarboxylic acid benzyl ester as an orange oil