N-Acyl-N-alkylcarbamoyloxy radicals: Entries to amidyl radicals by decar☐ylation and to α-amide radicals by radical translocation

Esker, John L.; Newcomb, Martin

doi:10.1016/s0040-4039(00)61087-0

Cited by 35 publications

(13 citation statements)

References 11 publications

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“…Syntheses. Three types of amidyl radical precursors were used in this work, N-acyl PTOC carbamates 6 (A), PTOC imidate esters 5 (I), and N-(phenylthio)amides 7 (P). Each was prepared from the corresponding amide by literature methods as shown in Scheme 1.…”

Section: Resultsmentioning

confidence: 99%

“…Among the three radical precursors employed for LFP studies in this work, the N-acyl PTOC carbamates are quite useful due to their ease in preparation, their relative stability, and their reactivity in chain reactions with thiyl radicals. 6 In addition, they are cleaved by 355-nm light which does not interfere with the observation of UV absorbances from benzylic and diphenylalkyl radicals that have λ max values in the 320-and 335-nm range, respectively. However, the first-formed radicals from these precursors are amidylacyloxyl radicals 18 that can react by an intramolecular hydrogen atom transfer to give R-amide radicals 19 in addition to the desired decarboxylations that give amidyl radicals.…”

Section: Discussionmentioning

confidence: 99%

“…Reactions of Amidylacyloxyl Radicals. Among the three radical precursors employed for LFP studies in this work, the N -acyl PTOC carbamates are quite useful due to their ease in preparation, their relative stability, and their reactivity in chain reactions with thiyl radicals . In addition, they are cleaved by 355-nm light which does not interfere with the observation of UV absorbances from benzylic and diphenylalkyl radicals that have λ max values in the 320- and 335-nm range, respectively.…”

Section: Discussionmentioning

confidence: 99%

“…In recent years, several new amidyl radical precursors have been reported that are available from mild reaction conditions and react cleanly in radical chain propagation steps. These include members of the PTOC family of radical precursors , (see Figure for examples), N -(phenylthio)amides, and thiocarbazone derivatives . Each of these amidyl radical precursors will react in chain propagation steps with stannyl (and one assumes also silyl) radicals, and the PTOC derivatives also will propagate chain reactions involving thiyl and selenyl radicals.…”

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Absolute Kinetics of Amidyl Radical Reactions

et al. 1998

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An absolute kinetic scale for amidyl radical reactions was established by a combination of direct laser flash photolysis (LFP) and indirect competition kinetic studies. Six amidyl radicals were studied by LFP. Arrhenius parameters were determined for 6-exo cyclizations of the N-butyl-6,6-diphenyl-5-hexenamidyl radical (2) and the N-butyl-6-(trans-2-phenylcyclopropyl)-5-hexenamidyl radical (5) and for 1,5-hydrogen transfer in the N- (6,6-diphenyl-5-hexenyl)acetamidyl radical (3); rate constants for these reactions at 20 °C are 3.0 × 10 7 s -1 (2), 5.5 × 10 6 s -1 (3), and 1 × 10 7 s -1 (5). Kinetic limits were established by LFP for the fast cyclizations of the N-methyl-5,5-diphenyl-4-pentenamidyl radical (1) and the N-methyl-5-(trans-2-phenylcyclopropyl)-4-pentenamidyl radical (4) (k > 2 × 10 8 s -1 at ambient temperature) and for the slow fragmentation of the N-(2,2-diphenylethyl)acetamidyl radical (6) (k ) 2 × 10 4 s -1 at 48 °C). Rate constants for amidyl radical reactions with Bu 3 SnH and PhSH were determined by competition kinetics; respective rate constants are 1.3 × 10 9 M -1 s -1 at 20 °C and 9 × 10 7 M -1 s -1 at 23 °C. Cyclizations of simple amidyl radicals were determined from competition kinetic studies by employing Bu 3 SnH and N-(phenylthio)amide radical precursors using data from the literature and from studies in this work. Rate constants at 65 °C for 5-exo cyclizations of the N-butyl-4-pentenamidyl radical and the N-(4-pentenyl)butanamidyl radical and for 6-exo cyclization of the N-ethyl-5-hexenamidyl radical are 3 × 10 9 s -1 , 7 × 10 8 s -1 , and 1.0 × 10 7 s -1 , respectively. The kinetic values determined in this work can be employed in synthetic planning involving amidyl radicals, and the simple amidyl radical clocks can be used for measuring rate constants of bimolecular reactions. A compilation of the kinetics of nitrogen-centered radical cyclizations and bimolecular reactions of nitrogen radicals with Bu 3 SnH and PhSH is presented.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Absolute Kinetics of Amidyl Radical Reactions

et al. 1998

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“…The core challenge can be attributed to the deficiency of a convenient route for the generation of relatively stable nitrogen-centred radical species. [4][5][6][7] Recently, Grützmacher and co-workers succeeded in the isolation of a stable metalcoordinated aminyl radical complexes and highlighted the potential role of their application as a hydrogen-atom abstractor. [8] It was recognized that an equilibrium existed between an M(n+1) amide and M(n) aminyl through a redox procedure (Scheme 1).…”

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confidence: 99%