A mixture of Example 4C (810 mg, 2.49 mmol), (S)-(5-oxopyrrolidin-2-yl)methyl 4-methylbenzenesulfonate (Aldrich, 807 mg, 3 mmol), potassium carbonate (828 mg, 6 mmol), tetrabutylammonium iodide (20 mg, 0.05 mmol), tetrabutylammonium hydrogensulfate (20 mg, 0.06 mmol) and tetraethylammonium iodide (20 mg, 0.07 mmol) in anhydrous toluene (100 mL) was refluxed for 15 h. The mixture was cooled to room temperature, washed with water, brine, dried with anhydrous MgSO4, filtered, and concentrated under reduced pressure. The residue was chromatographed (SiO2, ethyl acetate-ethanol 9:1) to afford 510 mg of the title compound. 1H NMR (300 MHz, DMSO-d6) δ 1.32 (s, 9H), 1.83 (m, 1H), 2.07 (m, 3H), 3.78 (s, 3H), 4.09 (m, 2H), 4.30 (m, 1H), 7.10 (d, J=9 Hz, 1H), 7.27 (s, 1H), 7.45 (dd, J=9 Hz, 3 Hz, 1H), 7.62 (d, J=3 Hz, 1H), 7.82 (broad s, 1H); MS (DCI/NH3) m/z 422 (M+H)+. Anal. calcd for C20H24ClN3O3S.0.25H2O: C, 56.33; H, 5.79; N, 9.85. Found: C, 56.42; H, 5.55; N, 9.25.
