[S:1]([N:11]1[CH:15]=[CH:14][C:13]([C:16]([OH:18])=[O:17])=[CH:12]1)([C:4]1[CH:10]=[CH:9][C:7]([CH3:8])=[CH:6][CH:5]=1)(=[O:3])=[O:2].[C:19]1([CH3:25])[CH:24]=CC=C[CH:20]=1.C(OC(OC(C)(C)C)N(C)C)(C)(C)C>O>[S:1]([N:11]1[CH:15]=[CH:14][C:13]([C:16]([O:18][C:19]([CH3:25])([CH3:24])[CH3:20])=[O:17])=[CH:12]1)([C:4]1[CH:5]=[CH:6][C:7]([CH3:8])=[CH:9][CH:10]=1)(=[O:2])=[O:3]A 3-neck RBF was charged with 1-tosyl-1H-pyrrole-3-carboxylic acid (Astatech, Bristol, Pa.; 2.00 g, 7.54 mmol) and 20 mL anhydrous toluene, and was fitted with a water cooled reflux condenser and heated to reflux under N2. N,N-dimethylformamide di-tert-butyl acetal (Aldrich; 14.46 mL, 60.4 mmol) was added slowly dropwise via addition funnel. The reaction mixture was stirred for 1 h, then the oil bath was turned off, and the reaction mixture was cooled to RT over the weekend. It was partitioned between saturated aq. NaHCO3 and Et2O. The organic layer was washed with saturated aq. NaHCO3 once, saturated aq. NaCl once, and the organics were dried over anhydrous Na2SO4, filtered, and concentrated in vacuo. The material was treated with DCM and purified by silica gel chromatography (80 g column) using 0-20% EtOAc/hexanes. The product-containing fractions were concentrated to afford tert-butyl 1-tosyl-1H-pyrrole-3-carboxylate (287a; 2.22 g, 6.91 mmol, 92% yield) as a white solid. 1H NMR (400 MHz, CDCl3) δ ppm 7.80 (2H, d, J=8.4 Hz), 7.63-7.70 (1H, m), 7.33 (2H, d, J=8.2 Hz), 7.09 (1H, dd, J=3.3, 2.3 Hz), 6.61 (1H, dd, J=3.3, 1.6 Hz), 2.43 (3H, s), 1.53 (9H, s). m/z (ESI, +ve) 266.0 (M+H)+.
Wird geladen…
