[CH2:1]([O:4][C:5]1[CH:14]=[CH:13][C:8]2[S:9]C(=O)[O:11][C:7]=2[CH:6]=1)[CH:2]=[CH2:3].C1COCC1>[OH-].[Na+]>[CH2:1]([O:4][C:5]1[CH:14]=[CH:13][C:8]([SH:9])=[C:7]([OH:11])[CH:6]=1)[CH:2]=[CH2:3]6-(Allyloxy)-1,3-benzoxathiol-2-one (48.3 g, 0.232 mol) was dissolved in aq. NaOH solution (2M, 300 ml) and THF (300 ml) to give a yellow solution which stirred at RT for 2 h. The THF was removed in vacuo, a small amount of precipitated starting material removed by filtration, and further starting material was removed by extraction of the aqueous phase into diethyl ether (3×300 ml). The aqueous phase was then acidified to pH 1 with cHCl (˜150 ml) with ice-cooling. Gas evolution was observed, and after 15 min, the title compound was obtained following extraction into diethyl ether (3×300 ml), drying over MgSO4 and concentration to a yellow oil (37.84 g, 0.18 mol).
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