Difluoro-lambda3-bromane-induced Hofmann rearrangement of sulfonamides: synthesis of sulfamoyl fluorides.

We report the first example of Hofmann rearrangement of primary arenesulfonamides, which relies on the use of p-trifluoromethylphenyl(difluoro)-lambda(3)-bromane and affords N-arylsulfamoyl fluorides selectively at room temperature. Reaction of aryl-lambda(3)-iodanes with p-toluenesulfonamide affords sulfonylimono-lambda(3)-iodanes, being excellent progenitors for generation of metal-nitrenoid species. In marked contrast, reaction of the difluoro-lambda(3)-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-CF(3)) efficiently undergoes the lambda(3)-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-lambda(3)-iodanyl and aryl-lambda(3)-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.