Regioselective Reduction of 2-(Arylideneamino)isoindole-1,3-diones − Synthesis of Alkaloid Analogues by N-Acylhydrazonium Ion Aromatic π-Cyclization

Hydroxylactams 6a−c and 7a−c were synthesized by successive regioselective reductions of arylideneaminophthalimides 3a−c, which were easily available from aminophthalimide 1 and benzaldehyde (2a) or thiophenecarboxaldehydes 2b and 2c. N‐Acylhydrazonium ions III, generated in the presence of Lewis acid from acetoxy derivatives 8a and 9a of hydroxylactams 6a and 7a, or in organic acid medium directly from hydroxylactams 6b and 6c, induced the expected isoindolo‐phthalazines 10a and 11a and thienopyridazino‐isoindolones 12b and 12c. On the other hand, hydroxylactams 7b and 7c under acidic conditions gave the unexpected N‐thienylmethyl‐substituted thienopyridazino‐isoindolones 13b and 13c. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)