[CH3:1][C:2]1([C:12]([OH:14])=[O:13])[S:9](=[O:11])(=[O:10])[C:5]2[S:6][CH:7]=[CH:8][C:4]=2[CH2:3]1.C([Li])CCC.[S:20](=[O:22])=[O:21].Cl.[NH2:24]OS(O)(=O)=O>C1COCC1.[OH-].[Na+]>[O:10]=[S:9]1(=[O:11])[C:5]2[S:6][C:7]([S:20](=[O:22])(=[O:21])[NH2:24])=[CH:8][C:4]=2[CH2:3][C:2]1([CH3:1])[C:12]([OH:14])=[O:13]
A mechanically stirred solution of 2-methyl-2,3-dihydrothieno[2,3-b]thiophene-2-carboxylic acid-1,1-dioxide (13.9 g, 0.060 mol) in THF (400 mL, dry) was cooled to -78° C. under a nitrogen atmosphere. n-Butyllithium (47.7 mL, 2.5M solution in hexane) was added via syringe at such a rate that the internal temperature remained <-75° C. By the end of the addition (approximately 30 minutes) a very heavy precipitate had formed. The reaction was stirred at -78° C. for 1.25 hours and the sulfur dioxide was condensed into the reaction over a period of 15 minutes. The reaction was stirred for an additional 15 minutes at -78° C. then warmed to room temperature. The solvent was removed in vacuo to give a white solid, which was taken up in dilute sodium hydroxide. The pH was adjusted to 7 with HCl and hydroxylamine-O-sulfonic acid (2 eq, 13 g, 0.119 mol) was added. The clear solution was stirred overnight, and the separated oil extracted with ethyl acetate (2×400 mL). The organic phases were combined and washed with saturated brine and dried over magnesium sulfate. Filtration and evaporation of solvent left a white solid which was triturated with diethyl ether. The product was dried under vacuum to give the title compound as a white solid (14.5 g, 78% yield).
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