The reaction of 2-R-5,5-diethyl-2-ethynylpyrrolidin-1-oxyls (where R = Et, i-Pr) with esters of azidoacetic and p-azidobenzoic acids in the presence of copper(I) salts has been studied. It was found that the presence of the bulky isopropyl substituent prevents the reaction with ethyl ether of p-azidobenzoic acid and decreases the yield of the corresponding triazole in the reaction with methyl ester of azidoacetic acid. The resulting nitroxides demonstrated a high degree of resistance to reduction by ascorbic acid, which was comparable to the stability of 3,4-bis-hydroxymethyl-2,2,5,5-tetraethylpyrrolidin-1-oxyl.
GULMAN et al. (Fri,) studied this question.