Difluoro-λ³-bromane-induced hofmann rearrangement of sulfonamides: Synthesis of sulfamoyl fluorides

(Chemical Equation Presented) We report the first example of Hofmann rearrangement of primary arenesulfonamides, which relies on the use of p-trifluoromethylphenyl(difluoro)-λ³-bromane and affords N-arylsulfamoyl fluorides selectively at room temperature. Reaction of aryl-λ³-iodanes with p-toluenesulfonamide affords sulfonylimono-λ³-iodanes, being excellent progenitors for generation of metal-nitrenoid species. In marked contrast, reaction of the difluoro-λ³-bromane with p-toluenesulfonamide in benzene produced unique N-p-tolylsulfamoyl fluoride in a high yield, through Hofmann rearrangement. Arenesulfonamides with electron-donating (p-MeO and o-Me) and -withdrawing substituents (p-F, p-Cl, and p-CF₃) efficiently undergoes the λ³-bromane-induced Hofmann rearrangement. The structure of N-p-tolylsulfamoyl fluoride was determined by a single-crystal X-ray analysis. The differences in nucleofugality between aryl- λ³-iodanyl and aryl-λ³-bromanyl groups, the later being greater, probably play a pivotal role in determining the reaction course. The results obtained from the reaction of 2,3,5,6- tetramethylbenzenesulfonamide strongly suggest that generation of sulfonyl nitrene will not be involved in this rearrangement.