C([Li])CCC.[CH3:6][C:7]1([CH3:18])[CH:16]=[CH:15][C:14]2[C:9](=[CH:10][CH:11]=[C:12](Br)[CH:13]=2)[O:8]1.[S:19](=[O:21])=[O:20].[Li].C[O-].[Na+:25]>CCCCCC.[Na]>[CH3:6][C:7]1([CH3:18])[CH:16]=[CH:15][C:14]2[C:9](=[CH:10][CH:11]=[C:12]([S:19]([O-:21])=[O:20])[CH:13]=2)[O:8]1.[Na+:25]A 1.5M solution of butyllithium in hexane (5.2 ml) was added to a stirred solution of 2,2-dimethyl-6-bromochromene [prepared by the procedure described in Bull. Chem. Soc. Jap., 1982, 55(4) 1153] (2.0 g, 8.4 mM) in sodium dried ether (24 ml). The mixture was stirred for 3 hours, then cooled to -20° C. and treated with excess gaseous sulphur dioxide, whereupon the lithium sulphinate salt immediately began to separate out as a solid. The resultant suspension was stirred rapidly for one hour and then allowed to attain ambient temperature. The solid precipitate of lithium 2,2-dimethylchromene-6-sulphinate was collected by filtration and washed with dry acetone and sodium dried ether. The lithium salt was then dissolved in water and the solution acidified to pH 1 and extracted with ethyl acetate. The combined extracts were dried (Na2SO4) and evaporated. The resultant 2,2-dimethylchromene-6-sulphinic acid was dissolved in methanol (10 ml) containing sodium methoxide (400 mg, 7.3 mmol). After 10 minutes, the methanol was removed in vacuo to leave a solid residue of sodium 2,2-dimethylchromene-6-sulphinate, which was dried by azeotropic distillation with toluene in vacuo and used directly in the above reaction.
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