Stable nitroxyl radicals with triple bonds: 4-acetylenyl-3-imidazoline-3-oxide-1-oxyls

Synthesis and properties of the first representatives of terminal acetylenes in 3-imidazoline-1-oxyl 3-oxide series

“…ESR spectra of all the synthesized ethynyl substituted nitroxides 5, 6 have the typical for 3 imidazoline radicals character, as in case of related disubstituted acetylenes (see data in Ref. 6), and show that the spin density in them is localized only on the N-• O fragment.…”

“…6), and show that the spin density in them is localized only on the N-• O fragment. In this connection, we report the ESR spectra parameters for one compound 5 only (spectra for the other compounds will be reported in the next publication).…”

Peculiarities of chemical properties of cyclic nitrones and their use in organic synthesis

“…9 Crotone-type products 9 have been obtained in reactions of 4-methyl-3-imidazoline-3-oxide (1a) (R 2 =OH) with benzaldehyde and its derivatives ArCHO, where Ar = p-ethynyl -, p-bromoand p-iodo-phenyl groups ( Scheme 4). 6,11,12 Alkyl nitrones 1 can be metallized upon treatment with phenyl lithium in ether solution, producing Li-derivatives which react with carboxylic acid esters to give β-oxo nitrones 10 -the analogues of β-diketones. 13 With the help of the 13 C NMR method it has been found that β-oxo nitrones 10 exist as an equilibrium mixture of three tautomeric forms with the prevalence of enol nitrone C and enhydroxyamino nitrone B forms.…”

Epimerization of the α Stereocenter in d‐Ribose‐Derived Nitrones: Direct Access to Variant Quinolizidines with d‐Ribo and d‐Arabino Configurations

“…Formation of enehydroxylamines from nitrones and reactivity of nitrone a-carbona tom is well-known in the literature, starting from basic aldol-typec ondensations of simple nitrones through equilibrium studies of b-oxonitrones to the most recent asymmetric additions of nitrones and their silyl ethers to ketones. [10][11][12] Thus, under the reaction conditions, nitrone I obtained from protected ribose 1 must isomerize to enehydroxylamine II,w hich can either retautomerize to I or tautomerize to the new nitrone III,w hich is formally ad erivativeo fd-arabinose (Scheme 2). Then, nitrones I and III undergo highly stereoselective intramolecular 1,3-DC to give 3a and 4 respectively.I ts hould be pointed that the configuration of the a stereocenter in the nitrones determines the configurations of the newly formed stereocentersi nt he products while the influence of the stereogenic centers at the b and g positions seems negligible.…”

“…Although examples of reactions of nitrones at the a carbon and nitrone-enehydroxylamine equilibrium are known, [10][11][12] limited reports on epimerization of nitrones have been published solely for a-hydroxynitrones, [13] whereas no epimerization of ahydroxynitrones also occurs. [14] However,t ot he best our knowledge,n oe pimerizationw as reported so far for nitrones possessing ap rotected hydroxy group at the a position.…”