REACTION OF 1-SUBSTITUTED PYRROLES WITH N-FLUORODIBENZENESULFONIMIDE - EFFECT OF HALOGEN ON ELECTROPHILIC SUBSTITUTION BY ADDITION-ELIMINATION

The reaction of 1-substituted pyrroles (1-methyl, 1-ethyl and 1-phenyl ) with N-fluorodibenzenesulfonimide (NFSi) gave N-(1-substituted 1H-py rrol-2-yl)dibenzenesulfonimides as products by addition elimination. D efluorination of NFSi was the only competing reaction. In contrast the reaction of 1-t-butylpyrrole with NFSi gave a mixture of fluoropyrrol es. This is attributed to a steric interaction between the t-butyl gro up and the phenyl groups on NFSi. N-Chlorodibenzenesulfonimide was fou nd to dechlorinate under all conditions studied and it was not possibl e to compare its reactivity with that of NFSi. The results of this stu dy support our hypothesis that the observation of addition-elimination in pyrroles is related to the pi-electron donating ability of the hal ogen initially introduced into the ring.