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)