Abstract
Synthetic access to 7-CF3-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl radicals containing 4-(6-hydroxyhexyloxy)phenyl, 4-hydroxymethylphenyl or 3,5-bis(hydroxymethyl)phenyl groups at the C(3) position and their conversion to tosylates and phosphates are described. The tosylates were used to obtain disulfides and an azide with good yields. The Blatter radical containing the azido group underwent a copper(I)-catalyzed azide–alkyne cycloaddition with phenylacetylene under mild conditions, giving the [1,2,3]triazole product in 84% yield. This indicates the suitability of the azido derivative for grafting Blatter radical onto other molecular objects via the CuAAC “click” reaction. The presented derivatives are promising for accessing surfaces and macromolecules spin-labeled with the Blatter radical.
Highlights
Functionalization of flat surfaces [1,2,3,4,5,6,7,8,9], polymers [10,11,12,13,14], well-defined macromolecules, and nanoparticles [25,26,27,28,29,30] with stable radicals is becoming an important avenue for obtaining materials [31,32] for advanced technologies [33], which include organic electronics [11,34], spintronics [1,3,6], contrast agents in bioimaging [15,35,36], and energy storage [12,37,38,39]
Phenyllithium was reacted with benzo[e][1,2,4]triazines 1–3, and the resulting anions were oxidized with air to the corresponding radicals Ia–IIIa, which were conveniently isolated by column chromatography (SiO2 support) in yields up to 92% (Scheme 1)
The key intermediates contain the hydroxyl group (X = OH, a), which could be used for grafting in condensation and addition reactions
Summary
Functionalization of flat surfaces [1,2,3,4,5,6,7,8,9], polymers [10,11,12,13,14], well-defined macromolecules (dendrimers [15,16,17,18], cyclodextrins [19,20,21,22], fullerene [23], and nanotubes [24]), and nanoparticles [25,26,27,28,29,30] with stable radicals is becoming an important avenue for obtaining materials [31,32] for advanced technologies [33], which include organic electronics [11,34], spintronics [1,3,6], contrast agents in bioimaging [15,35,36], and energy storage [12,37,38,39]. One of the most efficient grafting methods involves the Cu(I)-catalyzed [3+2] cycloaddition (“click”) reaction between an azide and a terminal alkyne, leading to the formation of the [1,2,3]triazole ring with the 1,4-substitution pattern [47,48,49] This approach has been applied to grafting ethynyl-containing radicals into systems with pending azido groups [24,25,29,50]. It should be added that radical polymers have been obtained by polymerization of monomers containing stable radicals using, e.g., Rh catalysts, ring opening metathesis polymerization (ROMP), and electropolymerization methods [13,14,40]
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