Sulfuric Acid → 3-(Toluene-2-sulfonylamino)-thiophene-2-carboxylic acid tert-butyl ester
Reaction equation
[C:1]1([CH3:19])[C:2]([S:7]([NH:10][C:11]2[CH:15]=[CH:14][S:13][C:12]=2[C:16]([OH:18])=[O:17])(=[O:9])=[O:8])=[CH:3][CH:4]=[CH:5][CH:6]=1.OS(O)(=O)=O>>[C:1]([O:17][C:16]([C:12]1[S:13][CH:14]=[CH:15][C:11]=1[NH:10][S:7]([C:2]1[C:1]([CH3:19])=[CH:6][CH:5]=[CH:4][CH:3]=1)(=[O:9])=[O:8])=[O:18])([CH3:19])([CH3:2])[CH3:6]Participants
3
Procedure
To a cold (−40° C.) mixture of 3-(Toluene-2-sulfonylamino)-thiophene-2-carboxylic acid (1.5 g, 5.05 mmol) in 1,4-dioxane/CHCl, (1:2, 12 mL) was bubbled 2-methyl-2-propene gas (15 mL) in a sealed tube. To this was added Conc. H2SO4 (0.070 mL, 1.3 mmol) and slowly warmed up to room temperature. The resultant reaction mixture was heated at 70° C. for 2.5 days in a sealed tube, cooled to −40° C., stopper was removed. The reaction mixture was slowly brought up to room temperature and stirred until the excess gas is released. The mixture was extracted with EtOAc, washed with aq. NaHCO3 solution, brine and dried. Evaporation of the solvent and purification of the residue on silica gel using EtOAc/hexane (1:10) as an eluent furnished 3-(Toluene-2-sulfonylamino)-thiophene-2-carboxylic acid tert-butyl ester (1.31 g, 73.5% based on 90% conversion). 1H NMR (CDCl3, 300 MHz) 9.89 (s, 1H), 8.01 (d, J=7.9 Hz, 1H), 7.43 (dt, J=7.5 Hz, 1.5 Hz, 1H), 7.3-7.25 (m, 3H), 7.2 (d, J=5.4 Hz, 1H), 2.69 (s, 3H), 1.56 (s, 9H).