Alkynyl compounds carrying unpaired electrons in remote substituents

1 Alkynyl Compounds Carrying Unpaired Electrons in Remote Substituents 

In a pioneering study, Rieker et al. prepared a series of 4-(yJ-substituted ethynyl)-2,6-di-/erf-butylphenols (1 and the analogs), oxidized them to the corresponding phenoxyls 2-5 with alkaline K3[Fe(CN)g] solution, Pb02 or 2,6-di-ferf-butyl-4-cyanophenoxyl under a nitrogen 

II Building Blocks for High-Spin Molecules and Molecular Assemblies 

Nitroxide radical 6 is similar in that it is stable in deoxygenated solution but cannot be isolated as free-radical solid. The n-spin density at the terminal ethynyl carbon atom is estimated from the value of 1.3 G to be 0.05 [5]. 

A pair of Ullman s nitronyl nitroxide radicals carrying m- and p-ethynylphenyl groups at position 2 of the imidazoline ring (7 and 8) are quite stable at room temperature under air and the unpaired electrons withstand the catalyzed polymerization conditions (see Section 11.4.3) [6]. The terminal ethynyl groups are not susceptible to Pb02 in benzene/metha-nol at room temperature, which is used for the oxidation of the bis(hydroxylamine)s to the nitronyl nitroxides [6, 7]. Fremy s salt gives the best result for the oxidation of the hydroxyl-amine 14 carrying a terminal 1,3-butadiyne moiety [9]. 

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