Pd. Bailey et al., NOVEL SPIRO CYCLIZATIONS OF N-ACYLIMINIUM IONS INVOLVING AN AROMATIC PI-NUCLEOPHILE, Tetrahedron letters, 35(38), 1994, pp. 7115-7118
Several spiro 2-pyrrolidin-5-ones were obtained by a two-step procedur
e from N-substituted succinimides, involving spiro cyclisation of N-ac
yliminium ion intermediates in refluxing trifluoroacetic acid; in all
cases cyclisation utilised a tethered aromatic pi-nucleophile, and rin
g-closure followed 5- or 6-exo-trig pathways.