An investigation into the electrophilic cyclisation of N-acyl-pyrrolidinium ions: a facile synthesis of pyrrolo-tetrahydroisoquinolones and pyrrolo-benzazepinones.

The triflic acid-mediated cyclisation of N-arylmethyl- and N-arylethyl-acylpyrrolidinium ions gave moderate to good yields of pyrrolo-tetrahydroisoquinolones and pyrrolo-benzazepinones respectively. Electron-donating R substituents enhanced the rate of reaction and gave higher yields than electron-withdrawing substituents. Substituents on the methyl or ethyl chain in general enhanced the reaction, unless sterically encumbered. The equivalent acylpiperidinium ions cyclised much slower and in lower yield.