Radical ion probes. 2. Evidence for the reversible ring opening of arylcyclopropylketyl anions. Implications for mechanistic studies

Tanko, James M.; Drumright, Ray E.

doi:10.1021/ja00031a045

Cited by 71 publications

(38 citation statements)

References 1 publication

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“…The cyclopropyl carbinol derivatives (entries 1–3) show no ring-opening to the homoallylic products. 22,23 Cyclopropyl radical ring-opening is known to be a reversible process, 24 but the lack of trans–cis isomerization of 2,3- trans , trans -diphenyl-cyclopropanemethanol (entry 3) indicates that a ring-opening/ring-closure equilibrium does not occur. Cyclobutanol affords only cyclobutanone (entry 4), and no cyclizaton of the benzylic alcohol is observed under the reaction conditions (entry 5).…”

Section: Resultsmentioning

confidence: 99%

Mechanism of Alcohol Oxidation Mediated by Copper(II) and Nitroxyl Radicals

et al. 2014

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2,2′-Bipyridine-ligated copper complexes, in combination with TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl), are highly effective catalysts for aerobic alcohol oxidation. Considerable uncertainty and debate exist over the mechanism of alcohol oxidation mediated by CuII and TEMPO. Here, we report experimental and density functional theory (DFT) computational studies that distinguish among numerous previously proposed mechanistic pathways. Oxidation of various classes of radical-probe substrates shows that long-lived radicals are not formed in the reaction. DFT computational studies support this conclusion. A bimolecular pathway involving hydrogen-atom-transfer from a CuII–alkoxide to a nitroxyl radical is higher in energy than hydrogen transfer from a CuII–alkoxide to a coordinated nitroxyl species. The data presented here reconcile a collection of diverse and seemingly contradictory experimental and computational data reported previously in the literature. The resulting Oppenauer-like reaction pathway further explains experimental trends in the relative reactivity of different classes of alcohols (benzylic versus aliphatic and primary versus secondary), as well as the different reactivity observed between TEMPO and bicyclic nitroxyls, such as ABNO (ABNO = 9-azabicyclo[3.3.1]nonane N-oxyl).

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Section: Resultsmentioning

confidence: 99%

Mechanism of Alcohol Oxidation Mediated by Copper(II) and Nitroxyl Radicals

et al. 2014

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“…Subsequent reversible endergonic radical ring-opening of the cyclopropane moiety resulted in alkyl radical 157a. 122 Slow stepwise cycloaddition with alkene 158a resulted in a [Gd]-ketyl radical 159a. Chain-propagating electron transfer to another equivalent of the substrate or chain-terminating reduction of the amine radical cation 161 + resulted in the formation of 160a.…”

Section: Rutheniummentioning

confidence: 99%

Recent advances in visible light-activated radical coupling reactions triggered by (i) ruthenium, (ii) iridium and (iii) organic photoredox agents

2021

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“…15 Second, Tanko has reported that the ring-opening of similar cyclopropyl ketyl radicals is reversible and endergonic. 16 To validate this expectation, we monitored a reaction starting with the cis isomer of 4 and found that the cyclopropane was completely isomerized to the trans isomer within 1 h, well before the reaction was complete. This reversible cleavage is consistent with the observation that racemic β,β’-disubstituted cyclopropane 29 undergoes stereoconvergent cycloaddition to cyclopentyl ketone 30 in good diastereoselectivity and excellent ee (eq 2).…”

mentioning

confidence: 97%

Enantioselective Photocatalytic [3 + 2] Cycloadditions of Aryl Cyclopropyl Ketones

2016

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Control of stereochemistry in photocycloaddition reactions remains a substantial challenge, and almost all successful catalytic examples to date have involved [2+2] photocycloadditions of enones. We report a method for the asymmetric [3+2] photocycloaddition of aryl cyclopropyl ketones that enables the enantiocontrolled construction of densely substituted cyclopentane structures that are not synthetically accessible using other catalytic methods. These results show that the dual-catalyst strategy developed in our laboratory broadens synthetic chemists’ access to classes of photochemical cycloadditions that have not previously been feasible in enantioselective form.

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Radical ion probes. 2. Evidence for the reversible ring opening of arylcyclopropylketyl anions. Implications for mechanistic studies

Cited by 71 publications

References 1 publication

Mechanism of Alcohol Oxidation Mediated by Copper(II) and Nitroxyl Radicals

Mechanism of Alcohol Oxidation Mediated by Copper(II) and Nitroxyl Radicals

Recent advances in visible light-activated radical coupling reactions triggered by (i) ruthenium, (ii) iridium and (iii) organic photoredox agents

Enantioselective Photocatalytic [3 + 2] Cycloadditions of Aryl Cyclopropyl Ketones

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