44.48 g of KOtBu were dissolved in 800 ml of anhydrous DMF and, at RT, 45.44 g of guanidinium chloride were added. After stirring at RT for 1 hour, the solution was poured into a solution of 35.00 g of methyl 4-[4-(4-fluoro-phenyl)-1,1-dioxoisothiazolidin-2-yl]-5-methanesulfonyl-2-methylbenzoate in 300 ml of anhydrous DMF. The mixture was then stirred at RT for 5 hours. It was then poured into 2 l of water, adjusted to pH=8 with aqueous HCl solution and extracted 5 times with 300 ml of EA each time. After drying over MgSO4, the solvent was removed in vacuo.
