[3 + 2]-Dipolar Cycloaddition of Aldehyde-Tethered Alkynamides and Trimethylsilyl Amino Esters: A Gateway to Uniquely Functionalized Polycyclic N-Heterocycles via Post-Ugi Functionalization.

An efficient method for the generation of uniquely functionalized pyrrolo-pyrrolizinones, pyrido-pyrrolizinones, and azepino-pyrrolizinones via [3 + 2]-dipolar cycloaddition is described. The method involves the synthesis of tethered alkynamides using Ugi condensation and oxidation that were subsequently subjected to a dipolar cycloaddition reaction with trimethylsilyl amino esters. Further transformations to demonstrate the utility of these scaffolds were also investigated.