Copper-catalysed azide-alkyne cycloaddition of sterically shielded 2-ethynylpyrrolidin-1-oxyls
M. M. GULMAN1,2, YU. F. POLIENKO1, S. YU. TRAKHININA1, YU. V. GATILOV1, S. A. DOBRYNIN1,2, I. A. KIRILYUK1
1Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
Keywords: nitroxide, acetylenes, copper-catalysed azide-alkyne cycloaddition
Abstract
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.
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