Isolation and Magnetic Properties of Heterocycle-Carrying N-Alkoxyarylaminyl Radicals¹

Abstract

Two N-tert-butoxy-2,6-diaryl-4-(4-pyridyl)phenylaminyls (1) and three N-tert-butoxy-2,6-diaryl-4-(1H-imidazol-1-yl)phenylaminyls (2) were prepared by the reaction of the lithium salts of the corresponding anilines with tert-butyl peroxybenzoate. Although 1 could not be isolated as radical crystals, 2 was successfully obtained as red crystals. The X-ray crystallographic analysis and magnetic susceptibility measurements were performed for one isolated radical.

Synthesis of O-tert-Butyl-N,N-disubstituted Hydroxylamines by N–O Bond Formation

“…This strategy was extended to the synthesis of N -alkoxyaminyl radicals by Miura, − when as in the study by Benn and Meesters yields were modest at best and extremely sensitive to the steric nature of the nucleophile. We now report that the reaction of magnesium dialkylamides with an appropriately substituted TBPB derivative, tert -butyl 2,6-dimethyl perbenzoate, offers a practical method to access a wide array of O-tert -butyl- N,N -disubstituted hydroxylamines in a direct fashion by N–O bond formation without the inherent scope limitations previously observed − (Figure c). We also report that the well-documented − bias of amines to react selectively with peresters in a 1,2-fashion can be overcome by a modification of the perester electrophile.…”

“…In contrast, an early report by Benn and Meesters showed that sterically encumbered primary tert -alkyl lithium amides react with TBPB to afford O - tert -butyl- N -monosubstituted hydroxylamines by direct N–O bond formation in modest yields (Figure b) . This strategy was extended to the synthesis of N -alkoxyaminyl radicals by Miura, − when as in the study by Benn and Meesters yields were modest at best and extremely sensitive to the steric nature of the nucleophile. We now report that the reaction of magnesium dialkylamides with an appropriately substituted TBPB derivative, tert -butyl 2,6-dimethyl perbenzoate, offers a practical method to access a wide array of O-tert -butyl- N,N -disubstituted hydroxylamines in a direct fashion by N–O bond formation without the inherent scope limitations previously observed − (Figure c).…”

New Method for the Synthesis of N-tert-Alkoxyarylaminyl Radicals1

“…Interestingly, the N - tert -alkoxyarylaminyls are thermally very stable and do not react with oxygen. ,− In recent years, the isolable, stable, free radicals have attracted much attention as the spin source and building blocks in the study on organic magnetism. − Radicals 1 − 3 were generated by the reaction of the lithium salts of the corresponding 2,4,6- trisubstituted anilines with tert -alkylperoxybenzoates in THF at −78 °C. ,− Although the above method is convenient, there are some problems. For example, the isolated radical yields are low, ,− (12−27%) and the use of butyllithium in the radical syntheses refuses the presence of functional groups. To overcome these problems, much effort has been paid, and we have now established a new convenient method for the synthesis of N - tert -alkoxyarylaminyls .…”

Electrochemical study of stable N-alkoxyarylaminyl radicals

“…Although N-alkoxyaminyl radicals were extensively studied by ESR spectroscopy over a long time [1][2][3][4][5][6][7][8][9][10], the first isolation of N-alkoxyaminyls by our group was quite recent [11][12][13][14][15][16][17]. We obtained isolable N-alkoxyarylaminyls by two methods.…”

“…We obtained isolable N-alkoxyarylaminyls by two methods. One method involves the reaction of the lithium salts of 2,4,6-tri-substituted anilines with tert-alkyl peroxybenzoates [11][12][13][14][15] and the other involves the reaction of 2,4-diaryl-6-tert-butylnitrosobenzenes with azo compounds [16,17]. Interestingly, the isolated N-alkoxyarylaminyls are stable in the presence of oxygen even in solution and, although they were heated at 80 • C in benzene for 10 days, 80% of the radical survived.…”