N-Acyliminium ion cyclisation versus rearrangement. The synthesis of 13,13-dimethylberberines and 3,4-dimethylisoquinolin-1-ones

The regioselective reduction of a range of N-substituted-4,4-dimethylhomophthalimide derivatives gave the related carbinol amides that function as acyliminium ion precursors in the presence of Lewis or protic acids; the fate of the acyliminium ions is determined in part by the nucleophilicity of the β-arylethyl group on nitrogen, the electrophile used to generate the ion, and the precise reaction conditions and led either to cyclisation reactions or methyl migration.