Sterically shielded nitroxides of pyrrolidine series are known to demonstrate the highest stability to reduction. Here we report on the synthesis of new pyrrolidine nitroxides from 5,5-dialkyl-1-pyrroline N-oxides via the introduction of pent-4-enyl group to nitrone atom followed by intramolecular 1,3-dipolar cycloaddition reaction and isoxazolidine ring opening. Kinetics of reduction of the new nitroxides with ascorbate was studied and compared to that of previously published 1S,2R,3′S,4′S,5′S,2″R-dispiro[(2-hydroxymethyl)-cyclopentan-1,2′-(3′,4′-di-tert-butoxy)pyrrolidine-5′,1″-(2″-hydroxymethyl)cyclopentane]-1′-oxyl (1).