Photochemical reaction of oximes with quinones.  New method for the preparation of iminoxy radicals

Lin, Tien‐Sung; Mastin, Stephen H.; Ohkaku, Noboru

doi:10.1021/ja00801a061

Cited by 10 publications

(2 citation statements)

References 1 publication

(2 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Despite the many indications that ET is the preferred pathway, it cannot be completely ruled out that instead of an ET pathway the reaction proceeds via a hydrogen atom abstraction pathway . To obtain further evidence for the formation of the oxime ether radical cation under these conditions, the addition of variable concentrations of the electron donor (tris- p -anisylamine; TAA) was studied.…”

Section: Resultsmentioning

confidence: 99%

Photosensitized Reactions of Oxime Ethers: A Steady-State and Laser Flash Photolysis Study

Lijser

Tsai

2004

J. Org. Chem.

View full text Add to dashboard Cite

The mechanistic aspects of the photosensitized reactions of a series of oxime ethers were studied by steady-state (product studies) and laser flash photolysis methods. Nanosecond laser flash photolysis studies have shown that chloranil-sensitized reactions of the oxime ethers result in the formation of the corresponding radical cations. The radical cation species react with nucleophiles such as MeOH by clean second-order kinetics with rate constants of (0.7-1.4) x 10(6) M(-1) s(-1). Only a small steric effect is observed in these reactions, which is taken as an indication that the reaction center is not the O-alkyl moiety, but rather somewhere else in the molecule. Product studies in a polar nonnucleophilic solvent (MeCN) revealed that in order for the oxime ether radical cation to react more readily, alpha-protons must be available on the alkyl group. The O-methyl (1), O-ethyl (2), and O-benzyl (3) acetophenone oximes all reacted readily to give acetophenone oxime as the major product (as well as an aldehyde derived from the O-alkyl group), whereas O-tert-butyl acetophenone oxime (4) did not. The product formation can be explained by a mechanism that involves electron transfer followed by proton transfer (alpha to the oxygen) and subsequent beta-cleavage. When using 3 in MeOH, a change in the product formation is observed, the most important difference being the presence of benzyl alcohol rather than benzaldehyde as the major product. On the basis of the data from LFP and steady-state experiments, it is suggested that the competing mechanism under these conditions involves electron transfer, followed by a nucleophilic attack on the nitrogen, a MeOH-assisted [1,3]-proton transfer, and subsequent loss of benzyl alcohol. This mechanism is supported by DFT (B3LYP/6-31G) and AM1 calculations.

show abstract

Section: Resultsmentioning

confidence: 99%

Photosensitized Reactions of Oxime Ethers: A Steady-State and Laser Flash Photolysis Study

Lijser

Tsai

2004

J. Org. Chem.

View full text Add to dashboard Cite

show abstract

“…Various oxidants were used for the generation of iminoxyl radicals from oximes, including transition metal compounds, such as (NH 4 ) 2 Ce(NO 3 ) 6 [38,46], Fe(ClO 4 ) 3 [44,46], Cu(ClO 4 ) 2 [46], Pb(OAc) 4 [44,[46][47][48][49][50][51], PbO 2 [52], Mn(OAc) 3 [46], KMnO 4 [46], Ag 2 O [53], AgO [54], Horseradish peroxidase/H 2 O 2 [55], metal-free oxidants PhI(OAc) 2 [46], t-BuOOt-Bu [53] or quinones [56] under UV irradiation. Anodic oxidation was also reported [57].…”

Section: Reviewmentioning

confidence: 99%

Oxime radicals: generation, properties and application in organic synthesis

Krylov¹,

Paveliev²,

Budnikov³

et al. 2020

Beilstein J. Org. Chem.

View full text Add to dashboard Cite

N-Oxyl radicals (compounds with an N–O• fragment) represent one of the richest families of stable and persistent organic radicals with applications ranging from catalysis of selective oxidation processes and mechanistic studies to production of polymers, energy storage, magnetic materials design and spectroscopic studies of biological objects. Compared to other N-oxyl radicals, oxime radicals (or iminoxyl radicals) have been underestimated for a long time as useful intermediates for organic synthesis, despite the fact that their precursors, oximes, are extremely widespread and easily available organic compounds. Furthermore, oxime radicals are structurally exceptional. In these radicals, the N–O• fragment is connected to an organic moiety by a double bond, whereas all other classes of N-oxyl radicals contain an R2N–O• fragment with two single C–N bonds. Although oxime radicals have been known since 1964, their broad synthetic potential was not recognized until the last decade, when numerous selective reactions of oxidative cyclization, functionalization, and coupling mediated by iminoxyl radicals were discovered. This review is focused on the synthetic methods based on iminoxyl radicals developed in the last ten years and also contains some selected data on previous works regarding generation, structure, stability, and spectral properties of these N-oxyl radicals. The reactions of oxime radicals are classified into intermolecular (oxidation by oxime radicals, oxidative C–O coupling) and intramolecular. The majority of works are devoted to intramolecular reactions of oxime radicals. These reactions are classified into cyclizations involving C–H bond cleavage and cyclizations involving a double C=C bond cleavage.

show abstract

Light‐Induced Chemistry of Oximes and Derivatives

Roth¹

2010

Patai's Chemistry of Functional Groups

View full text Add to dashboard Cite

Photoreactions of oximes have been known for 120 years. The earliest recognized reaction was geometric isomerization, which is still the most prominent oxime photoreaction; it proceeds via a ππ* triplet state. More than sixty years later the intriguing photo‐Beckmann rearrangement came to light, a C–C=N–O to O=C–N–C conversion, generating, for example, ɛ‐caprolactam from cyclohexanone ξιμɛ. The rearrangement proceeds via a ππ* singlet state forming an oxazirane intermediate; the oxazirane ring usually opens in stereospecific fashion. Detailed insight into the stereo‐ and regiochemistry of the rearrangement was gained from steroidal oximes, the most thoroughly investigated class of oximes. Additional photoreactions of oximes or of their ethers and esters include: net loss of hydroxylamine generating carbonyl compounds; loss of water from aldoximes forming nitriles; conversion of ketoximes to nitriles by more complex mechanisms; photochemical O–H cleavage generating iminoxyl radicals, an interesting family of free radicals; N–O cleavage giving rise to iminyl radials, which undergo radical cyclizations. β,γ‐Unsaturated oximes undergo aza‐di‐π‐methane rearrangements, cyclize to oxazolines, and undergo further reorganizations. The palette of oxime reactions has been further enriched by triplet energy transfer or electron transfer sensitization; oximes serve as electron donors or acceptors.

show abstract

Photochemical reaction of oximes with quinones. New method for the preparation of iminoxy radicals

Cited by 10 publications

References 1 publication

Photosensitized Reactions of Oxime Ethers: A Steady-State and Laser Flash Photolysis Study

Photosensitized Reactions of Oxime Ethers: A Steady-State and Laser Flash Photolysis Study

Oxime radicals: generation, properties and application in organic synthesis

Light‐Induced Chemistry of Oximes and Derivatives

Contact Info

Product

Resources

About