Total synthesis of grandisine D (5) was achieved by a Brønsted acid mediated Morita−Baylis−Hillman (MBH) ring-closure reaction and stereoselective aldol condensation with (S)-5-methylcyclohexenone (9) as key steps. The MBH approach was also applicable for the construction of the aza-fused bicyclicsystems of pyrrolizidine and stemona alkaloids.
first total synthesis of grandisine alkaloids, grandisines B, D, and F, which show affinity for the human δ‐opioid receptor. The key steps in this synthesis are construction of the isoquinuclidinone moiety of 2 by intramolecularimine formation and the tetracyclic ring system of 4 by stereoselective ring closure of the enolate of amine 8 generated by 1,4‐addition of ammonia to 9. Synthesis of key intermediate