[CH2:1]([NH:3][S:4]([CH2:7][C:8]1[CH:13]=[CH:12][CH:11]=[CH:10][CH:9]=1)(=[O:6])=[O:5])[CH3:2].CC(C)([O-])C.[K+].[C:20](OCC)(=[O:24])[C:21]([O-])=[O:22].Cl>C1COCC1>[CH2:1]([N:3]1[C:21](=[O:22])[C:20]([OH:24])=[C:7]([C:8]2[CH:13]=[CH:12][CH:11]=[CH:10][CH:9]=2)[S:4]1(=[O:5])=[O:6])[CH3:2]N-Ethyl-1-phenylmethanesulfonamide (20 g) was divided into batches of 0.5 g each and taken in an 8 mL vial. To each vial was added potassium tert-butoxide (0.426 g, 3.8 mmol), ethyl oxalate (0.408 mL, 3.01 mmol) and dry THF (4 mL). Each vial was heated in a microwave reactor at 145° C. under pressure for 20 mins. Reaction mixture from all the vials were combined and treated with 1.5 N HCl (75 mL) and extracted with EtOAc. The organic layer was washed with water (3×25 mL) and brine, dried over Na2SO4 and evaporated. A small amount of the DCM was added to the solid residue and stirred well. Filtration gave nearly pure title compound (21 g, 82.6%) as off-white solid; 1H NMR (300 MHz, CDCl3) 1.47 (t, 3H, J=7.2 Hz), 3.8 (q, 2H, J=7.2 Hz), 7.3-7.5 (m, 3), 7.9-8.0 (m, 2H).
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