SYNTHESIS OF A TETRACYCLIC SUBSTRUCTURE OF MANZAMINE-A VIA THE DIELS-ALDER REACTION OF DIHYDROPYRIDINONES

Synthesis of the tetracyclic core (19) of manzamine A (I) was achieved via Diels-Alder reaction of the dihydropyridinones (5, 6). Conversion of the two D-A products (7, 8) to the key tricyclic ketone (10) was c onducted through a conventional pathway (Scheme Ill) as well as a new pathway developed (Scheme IV). For effective construction of the requi red azocine ring systems, model studies were carried out to find intra molecular amide formation by pentafluorophenyl ester and DPPA methods, which were successfully applied to the real substrate refurnish the t itled core structure (19). Copyright (C) 1996 Elsevier Science Ltd