[CH2:1]([O:3][C:4]([C:6]1[CH:11]=[CH:10][C:9]([S:12]([O-:15])(=O)=[O:13])=[CH:8][CH:7]=1)=[O:5])[CH3:2].[K+].O=P(Cl)(Cl)[Cl:19]>C(#N)C.S1(CCCC1)(=O)=O>[CH2:1]([O:3][C:4]([C:6]1[CH:11]=[CH:10][C:9]([S:12]([Cl:19])(=[O:15])=[O:13])=[CH:8][CH:7]=1)=[O:5])[CH3:2]A round bottom flask, fitted with a magnetic stir bar and a hose adapter connected to a source of nitrogen gas, was charged with a solution of potassium 4-ethoxycarbonylbenzenesulfonate (75.1 g) dissolved in a 3:1 (v/v) mixture of acetonitrile (300 mL) and sulfolane (100 mL). As the solution was stirred, POCl3 (55 mL) was added slowly and the stirring mixture was heated at 75° C. under a nitrogen atmosphere for 3 hours. The heterogeneous reaction mixture was allowed to cool to room temperature and was then concentrated using a rotary evaporator. The flask was then cooled in an ice bath and ice was added to the mixture in the flask. The product crystallized as a white solid and was filtered and washed with cold deionized water. The product was dried under vacuum at room temperature and 3 mmHg for 2 hours to afford 76 g of white solid.
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