Hydroalkoxylation of alkynes by a nitroxyl containing alcohol, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl: synthesis of spin-labeled enol ethers

Abstract

A series of spin-labeled enol ethers has been synthesized in 53-67% yields by superbasecatalyzed (KOH/DMSO suspension as a catalyst) hydroalkoxylation of alkynes (acetylene, phenylacetylene, 4-tert-butylphenylacetylene and 3-ethynylpyridine) by 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (4-hydroxy-TEMPO) under mild conditions (70-80 °C, 1.5-2 h). With unsubstituted acetylene, the hydroalkoxylation readily occurs at atmospheric pressure, yield of the corresponding vinyl ether being 53%.