First isolation of N-alkoxyaminyl radicals

Miura, Yozo; Tomimura, Tatsuya

doi:10.1039/b100698n

Cited by 29 publications

(21 citation statements)

References 13 publications

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“…Our research group has been interested in the development of C–N bond-forming methodologies based on nitrogen-centered radical intermediaries using domino strategies to obtain heterocyclic compounds with biological potential. In that sense, we had previously reported a cascade radical bicyclization process involving oxime ethers, where aryl radicals were generated and immediately added onto a C=N bond in order to produce neutral alkoxyaminyl 8 or alkyl-oxyaminyl 9 radicals, which were then subsequently captured by a double bond activated with groups: Ph, CN, or CO 2 Me. This process afforded heterocyclic compounds 5 exhibiting a pyrrolidine nucleus fused to the indene skeleton (Scheme 2), 9 whereas 1,5 hydrogen transfer and 6- exo - trig cyclization occurred to produce the side products 6 and 7 .…”

Section: Introductionmentioning

confidence: 99%

Synthesis of 1-Azaspiro[4.4]nonane Derivatives Enabled by Domino Radical Bicyclization Involving Formation and Capture of Alkoxyaminyl Radicals

et al. 2019

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The application of a domino radical bicyclization for the synthesis of compounds containing the 1-azaspiro[4.4]nonane skeleton in 11–67% yields as a mixture of diastereomers is described (trans configuration preference). This process involved formation and capture of alkoxyaminyl radicals. For this purpose, O-benzyl oxime ethers with a brominated or iodinated aromatic ring or a terminal alkynyl group and an alkenyl moiety were employed as starting materials. The bicyclization was initiated by 2,2′-azobisisobutyronitrile or triethylborane and promoted by Bu3SnH. The best results were obtained with O-benzyl oxime ethers containing an alkenyl moiety tethered to electron withdrawing groups or aryl substituents, whereas oxime radical precursor attached to methyl-substituted olefin precluded the capture of alkoxyaminyl radical, giving rise mainly to monocyclized product.

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Section: Introductionmentioning

confidence: 99%

Synthesis of 1-Azaspiro[4.4]nonane Derivatives Enabled by Domino Radical Bicyclization Involving Formation and Capture of Alkoxyaminyl Radicals

et al. 2019

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“…Nitrogen‐centered (aminyl) radicals are typically short‐lived, and have been detected as intermediates in a variety of chemical and biological processes 1. 2 To the best of our knowledge, only two known stable aminyl radicals have been reported (more than 30 years ago),3, 4 while a few others have recently been isolated as aminyl metal complexes and as heteroatom (e.g., O, S) stabilized aminyls 5–7…”

Section: Methodsmentioning

confidence: 99%

Isolation of the Triplet Ground State Aminyl Diradical

et al. 2010

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Nitrogen-centered (aminyl) radicals are typically short-lived, and have been detected as intermediates in a variety of chemical and biological processes. [1,2] To the best of our knowledge, only two known stable aminyl radicals have been reported (more than 30 years ago), [3,4] while a few others have recently been isolated as aminyl metal complexes and as heteroatom (e.g., O, S) stabilized aminyls. [5][6][7] Aminyl diradicals, in which the radical centers are connected through m-phenylene to form a planar crossconjugated p system devoid of stabilizing heteroatoms, are predicted by computational studies to possess a strong preference for a high-spin, triplet (S = 1) ground state, that is, a singlet-triplet energy gap (DE ST ) that is an order of magnitude greater than the thermal energy (RT) at room temperature. [8,9] Such a nitrogen-centered diradical with large DE ST values and persistence at room temperature may be relevant to the design of strongly paramagnetic relaxation reagents [10,11] as well as the development of magnetic materials and devices. [12,13] To date, the two known examples of aminyl diradicals have been examined only at very low temperature. Platz and coworkers first reported an aminyl diradical in a 2-methyltetrahydrofuran (2-MeTHF) matrix at about À195 8C. [14] Recently, we prepared an aminyl diradical with an S = 1 ground state that was persistent in solution at about À100 8C. [9] Herein we report the isolation of an S = 1 ground state aminyl diradical with a large DE ST value and persistence at room temperature. The synthesis of the aminyl diradicals 1 and 2 demonstrates the balance between maintaining an effective 2p p -2p p overlap that enhances electron spin-spin interactions (exchange coupling), and the adequate protection of the carbon and nitrogen atoms with significant spin densities within the diazapentacene backbone in order to achieve the stability required for isolation. This result is significant as the 2p p -2p p overlap is generally severely perturbed by the increased steric bulk that is required for achieving radical stability, and thus a combination of a large DE ST value and persistence at room temperature is not commonly accomplished. In addition, we detected an unexpected self-associated dimer of the S = 1 aminyl diradical 2 in 2-MeTHF solution; this species appears to resemble a p dimer. Notably, characterization of the dimer is facilitated by its unique zero-field splitting tensor (D). p Dimers of neutral organic radicals in solution are relatively rare and the reports of such phenomena are limited to those of S = 1 = 2 radicals. [15] Diradicals 1 and 2 were prepared from the corresponding diamines 5 and 6, which were obtained from diamine 3 (Scheme 1). [16] The structure of diamine 6 was confirmed by X-ray crystallography, and shows overcrowding of the bulky tert-undecyl groups so that the C À C bond axes that connect the two outer pendant benzene rings to the backbone bend outward (Figure 1). [17] This bending creates more space for the pendant benzene rings in order...

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“…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.…”

Section: Introductionmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%