[NH2:1][C@H:2]1[CH2:6][CH2:5][CH2:4][C@H:3]1[C:7]([O:9][CH2:10][CH3:11])=[O:8].[Cl:12][C:13]1[CH:18]=[CH:17][C:16]([S:19](Cl)(=[O:21])=[O:20])=[CH:15][CH:14]=1.C(N(CC)CC)C.C(OCC)C>O1CCCC1>[Cl:12][C:13]1[CH:18]=[CH:17][C:16]([S:19]([NH:1][C@H:2]2[CH2:6][CH2:5][CH2:4][C@H:3]2[C:7]([O:9][CH2:10][CH3:11])=[O:8])(=[O:21])=[O:20])=[CH:15][CH:14]=1
To a solution of cis-ethyl 2-aminocyclopentanecarboxylate (1.57 g, 10 mmol) in 50 mL tetrahydrofuran was added 4-chlorobenzenesulfonyl chloride (3.17 g, 15 mmol) and triethylamine (2.1 mL, 15 mmol). The reaction was stirred at room temperature for 4 h, then diluted into 100 mL diethyl ether and washed with 100 mL water. The organic layer was concentrated and purified by flash chromatography on a 120 g silica gel column with 10 to 40% ethyl acetate in hexane, 20 min gradient, to yield cis-ethyl 2-(4-chlorophenylsulfonamido)cyclopentanecarboxylate (3.05 g, 92%). 1H NMR (400 MHz, CDCl3) δ ppm 7.76-7.80 (2H, m), 7.43-7.47 (2H, m), 5.57 (1 H, d, J=8.56 Hz), 3.91-4.10 (2H, m), 3.70-3.81 (1H, m), 2.74 (1H, dt, J=8.31, 6.55 Hz), 1.64-1.98 (5H, m), 1.44-1.58 (1H, m), 1.18 (3H, t, J=7.05 Hz). LC/MS R.T.=2.00 min; [M+H]+=332.07; [M+Na]+=354.04.
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