Synthesis of (-)-Monanchoradin A and (-)-Crambescin A2 392 Based on a Cyclization-Carbonylation-Cyclization Cascade.

Syntheses of guanidino alkaloids (-)-monanchoradin A and (-)-crambescin A2 392 are described. The key feature of the syntheses is the cyclization-carbonylation-cyclization cascade of the optically active propargyl guanidine. The bicyclic guanidino cores bearing an asymmetric center and ester or carboxylic acid functionality were constructed in a single step. The carboxylic acid was then converted to (-)-monanchoradin A and (-)-crambescin A2 392.