Protonation of N-Vinylpyrroles with Superacids

At 0°C for several hours, cation 6 is transformed (via 1,2-hydride shift) into the expected thermodynamically more stable a-protonated form 7. Before this work. 

SCHEME 2.6 Protonation of N-vinylpyrroles with the superacidic system HS03p/SbF5. 

SCHEME 2.7 Formation of the double-charged cation from 2-phenyl-N-vinylpyrroles in the HS03F/SbF5 system. 

2-tert-butyl-N-vinylpyrrole does not form dication, probably, owing to the absence of rather effective delocalization of the positive charge. 

After nentralization of the mixture with saturated aqueous K2CO3, a product of intramolecular cyclization, 5-methylindano[2,3-fl]pyrrole (7% yield), has been isolated. 

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