Intramolecular 1,3-dipolar cycloaddition-mediated stereoselective synthesis of disubstituted cyclopentane: a simple model for the cyclopentane ring system of polycyclic oroidine alkaloids.

We present a diastereoselective synthesis of disubstituted cyclopentane 8 having a nitrogen-containing quaternary carbon center, which is found in axinellamine A (5) and related compounds. During this work, we found that the 1,3-dipolar cycloaddition product 24 immediately underwent intramolecular redox reaction at the newly formed morpholin-2-one moiety, thus affording disubstituted cyclopentane containing a tertiary amine (9) stereoselectively in good yield. The amine 9 was successfully converted into guanidine 31, which corresponds to 8, through iminium cation-enamine isomerization.