For the construction of the tricyclic core of manzamine A (l), the Diels-Alder reactions of some dihydropyridinones were surveyed. The N-protecting group of the dihydropyridinone played an important role in achieving a successful Diels-Alder reaction. In view of its electron-withdrawing character as well as its thermal stability, the ptolueneaulfonyl protecting group wa~ found to be best in our syntheais. An effective method for the ...
