Formaldehyde → 2-(Chloromethyl)-4-isopropyl-6-methoxybenzo[D]isothiazol-3(2H)-one 1,1-dioxide

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To a suspension of 24 g of paraformaldehyde (0.8 mole) and 86.4 g of chlorotrimethylsilane (1.6 moles) in 200 mL of 1,2-dichloroethane was added 0.8 ml anhydrous tin(IV) chloride and the resulting solution stirred on a steam bath for one hour. 4-Isopropyl-6-methoxysaccharin (51.4 g, 0.2 mole) was added to the clear solution and the mixture was refluxed for 18 hours, cooled to room temperature and poured into water. The organic layer was separated, washed with 50 mL of 2N sodium hydroxide solution, dried over anhydrous magnesium sulfate and concentrated under vacuum. The residue was purified by crystallization from ethyl acetate/hexane to give 57 g (87%) of 2-chloromethyl-4-isopropyl-6-methoxysaccharin, mp 151°.

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