Methods for preparation of heterobifunctional nitroxides: α,β-unsaturated ketones, β-ketoesters, cyano-nitro-derivatives

Abstract
The reactions of 1-oxyl-2,2,5,5-tetramethyl-3-pyrroline-3-carboxaldehyde (1), 1-oxyl-2,2,5,5-tetramethyl-3-cyano-3-pyrroline (2), ethyl 1-oxy(-2,2,5,5-tetramethyl-3-pyrroline-3-carbonyl carbonate (3), and N-(1-oxyl-2,2,5,5-tetramethyl-3-pyrroline-3-carbonyl)imidazolide (4) are investigated with several nucleophiles (dialkylcadmium, diethyl sodio-malonate, magnesium enolate of ethyl hydrogen malonate, nitromethane-anion) to obtain α,β-unsaturated ketones, β-ketoesters, or conjugated reaction products. Aldehyde 1 is reacted with several methyl ketones (acetylmethylene-triphenylphosphorane, acetophenone, 2-acetylpyridine, 4-phenyl-3-butyn-2-one) to give spin labeled polyenones. The reaction of 4-(1-oxyl-2,2,5,5-tetramethyl-3-pyrroline-3-yl)-2-buten-2-one (24a) with ethylenediamine gives 7,14-bis-(1-oxyl-2,2,5,5-tetramethyl-3-pyrroline-3-yl)-5,12-dimethyl-1,4,8,11-tetraazatetradeca-7,14-diene biradical (25).

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