Cyclopropanesulfonyl chloride → Ethyl 4-(cyclopropanesulfonamido)-2-methylcyclopentanecarboxylate

A solution of ethyl 4-amino-2-methylcyclopentanecarboxylate (15.0 g, 88.0 mmol) in DMF (210 mL) was cooled to about 0° C. in an ice bath. TEA (30.5 mL, 219 mmol) was added and stirring was continued at about 0° C. for about 15 min and then cyclopropanesulfonyl chloride (12.3 g, 88.0 mmol, Matrix) was added drop-wise. The resulting solution was stirred at about 0° C. for about 2 h. The ice bath was removed and the reaction mixture continued stirring at ambient temperature for about 3 h. The reaction was concentrated under reduced pressure and EtOAc (200 mL) and water (100 mL) were added. The layers were separated and the organic layer was washed with saturated aqueous NaHCO3 (60 mL) and brine (60 mL), dried over anhydrous MgSO4, filtered, and concentrated under reduced pressure to give a reddish brown oil. The crude material was purified by silica gel chromatography eluting with a gradient of 10-30% EtOAc in heptane to give ethyl 4-(cyclopropanesulfonamido)-2-methylcyclopentanecarboxylate (21.3 g, 88%) as a yellow oil: 1H NMR (CDCl3) δ 5.25 (d, J=9.9 Hz, 1H), 4.23-4.06 (m, 2H), 4.03-3.90 (m, 1H), 2.80 (td, J=3.1, 7.5 Hz, 1H), 2.46-2.30 (m, 2H), 2.29-2.14 (m, 2H), 1.97 (ddd, J=3.2, 4.2, 14.2 Hz, 1H), 1.42 (ddd, J=7.5, 11.5, 13.1 Hz, 1H), 1.29 (t, J=7.1 Hz, 3H), 1.20-1.14 (m, 2H), 1.02 (d, J=6.9 Hz, 3H), 1.00-0.96 (m, 2H).