Dissociation or Cyclization: Options for a Triad of Radicals Released from Oxime Carbamates

McBurney, Roy T.; Walton, John C.

doi:10.1021/ja402833w

Cited by 72 publications

(36 citation statements)

References 51 publications

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“…28 However, decarboxylation was rapid at room temperature for both N-mono- and N,N-disubstituted 81 such that they functioned as clean sources of aminyl radicals 82 (Scheme 16). The EPR spectral data (Table 1) and DFT computations (Figure 3) showed these aminyls to be π-type radicals reminiscent of secondary alkyl radicals.…”

Section: Interrogation Of Radical Motions and Mechanisms By Epr Spectmentioning

confidence: 99%

The Oxime Portmanteau Motif: Released Heteroradicals Undergo Incisive EPR Interrogation and Deliver Diverse Heterocycles

Walton

2014

Acc. Chem. Res.

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162

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ConspectusSelective syntheses are now available for compounds of many classes, based on C-centered radicals, exploiting a diverse range of mechanisms. The prospect for chemistry based around N- and O-centered radicals is probably more favorable because of the importance of heterocycles as biologically active materials. Heteroradical chemistry is still comparatively underdeveloped due to the need for safe and easy ways of generating them. Oxime esters appeared promising candidates to meet this need because literature reports and our EPR spectroscopic examinations showed they readily dissociated on photolysis with production of a pair of N- and O-centered radicals. It soon became apparent that a whole suite of benign oxime-containing molecules could be pressed into service. The bimodality of the oxime motif meant that by suitable choice of functionality the reactions could be directed to yield selectively products from either the N-centered radicals or from the O-centered radicals.We found that on one hand photolyses of acetophenone oxime esters of carboxylic acids yielded alicyclics. On the other hand, aromatic and heteroaromatic acyl oximes (as well as dioxime oxalates) afforded good yields of phenanthridines and related heterocycles. Easily prepared oxime oxalate amides released carbamoyl radicals, and pleasingly, β-lactams were thereby obtained. Oxime carbonates and oxime carbamates, available via our novel 1,1'-carbonyldiimidazole (CDI)-based preparations, were accessible alternatives for iminyl radicals and hence for phenanthridine preparations. In their second modes, these compounds proved their value as precursors for exotic alkoxycarbonyloxyl and carbamoyloxyl radicals.Microwave-assistance was shown to be a particularly convenient procedure with O-phenyl oxime ethers. The iminyl radicals generated from such precursors with alkene, alkyne, and aromatic acceptor substituents furnished pyrrole, quinoline, phenanthridine, benzonaphthiridine, indolopyridine, and other systems. Microwave irradiations with 2-(aminoaryl)alkanone O-phenyl oximes enabled either dihydroquinazolines or quinazolines to be obtained in very good yields.The fine quality of the EPR spectra, acquired during photolyses of all the O-carbonyl oxime types, marked this as an important complement to existing ways of obtaining such spectra in solution. Quantifications enabled SARs to be obtained for key reaction types of N- and O-centered radicals, thus putting mechanistic chemistry in this area on a much firmer footing. Surprises included the inverse gem-dimethyl effect in 5-exo-cyclizations of iminyls and the interplay of spiro- with ortho-cyclization onto aromatics. Insights into unusual 4-exo-cyclizations of carbamoyl radicals showed the process to be more viable than pent-4-enyl 4-exo-ring closure. Another surprise was the magnitude of the difference in CO2 loss rate from alkoxycarbonyloxyl radicals as compared with acyloxyl radicals. Their rapid 5-exo-cyclization was charted, as was their preferred spiro-cyclization onto aromatics. The first...

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Section: Interrogation Of Radical Motions and Mechanisms By Epr Spectmentioning

confidence: 99%

The Oxime Portmanteau Motif: Released Heteroradicals Undergo Incisive EPR Interrogation and Deliver Diverse Heterocycles

Walton

2014

Acc. Chem. Res.

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162

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“…[11,12] In principle, four sites of the two yne units of the yne-ynamide scaffold are available for attack by the thiyl radical, [13] which would eventually result in eight different products on the basis of aspecific exo/endo mode of cyclization. Only radical additions via 5-exo-dig cyclizations,which turn out to be the best computational options,a re discussed here.T he values are DG 343 in kcal mol À1 obtained at the UB3LYP [14] /6-311 ++G-(d,p) [15] level including solvent correction for CH 2 Cl 2 (PCM method [16] ;F igure 2). Only radical additions via 5-exo-dig cyclizations,which turn out to be the best computational options,a re discussed here.T he values are DG 343 in kcal mol À1 obtained at the UB3LYP [14] /6-311 ++G-(d,p) [15] level including solvent correction for CH 2 Cl 2 (PCM method [16] ;F igure 2).…”

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confidence: 99%

Alkyne Versus Ynamide Reactivity: Regioselective Radical Cyclization of Yne‐Ynamides

et al. 2019

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“…To modify the reaction condition, we adopted CDI as a carbonyl source for the synthesis of oxime carbamate derivatives. CDI is a comparatively cheaper, mild, and safer reagent, even though only few studies are reported in literatures for the synthesis of oxime carbamates …”

Section: Resultsmentioning

confidence: 99%

Synthesis of Secondary and Tertiary Oxime Carbamate Derivatives and their Structure‐Dependent Bioactivity

Sivakumar

Thanikachalam

Kim

et al. 2017

Bulletin Korean Chem Soc

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Biologically active novel piperidin‐4‐one oxime carbamates were synthesized from 3‐ethyl‐1‐methyl‐2,6‐diphenylpiperidin‐4‐one oxime, 1,1′‐carbonyldiimidazole (CDI), and primary or secondary amines in the presence of sodium hydride as base. Commercially available, cheaper, and safer CDI was utilized as carbonyl source, instead of toxic phosgene/triphosgene and carbon monoxide. The devised method is feasible for primary and secondary amines to make their corresponding oxime carbamate derivatives, through oxime–imidazolide intermediate, in high yield. When the antimicrobial activity of obtained oxime carbamate derivatives was investigated in comparison with streptomycin and amphotericin B as standards, the oxime carbamate containing heteroaromatic thiazole ring exhibits outstanding antimicrobial effectiveness, regardless of bacterial or fungal types.

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Dissociation or Cyclization: Options for a Triad of Radicals Released from Oxime Carbamates

Cited by 72 publications

References 51 publications

The Oxime Portmanteau Motif: Released Heteroradicals Undergo Incisive EPR Interrogation and Deliver Diverse Heterocycles

The Oxime Portmanteau Motif: Released Heteroradicals Undergo Incisive EPR Interrogation and Deliver Diverse Heterocycles

Alkyne Versus Ynamide Reactivity: Regioselective Radical Cyclization of Yne‐Ynamides

Synthesis of Secondary and Tertiary Oxime Carbamate Derivatives and their Structure‐Dependent Bioactivity

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