A Hofmann Rearrangement-Ring Expansion Cascade for the Synthesis of 1-Pyrrolines: Application to the Synthesis of 2,3-Dihydro-1H-pyrrolo[2,1-a]isoquinolinium Salts

Treatment of cyclobutanecarboxamide with bis(trifluoroacetoxy)iodobenzene, PhI(O-COCF3)(2), resulted in the formation of 1-pyrroline via Hofmann rearrangement of the former followed by in situ ring expansion reaction of the cyclobutylamine intermediate. Further elaboration of this methodology to the synthesis of 2,3-dihydro-1H-pyrrolo[2,1-a]isoquinolinium salts has also been described.