Synthesis of aliphatic nitriles from cyclobutanone oxime mediated by sulfuryl fluoride (SO₂F₂)

• Xian-Lin Chen and
• Hua-Li Qin

Beilstein J. Org. Chem. 2023, 19, 901–908, doi:10.3762/bjoc.19.68

• afford the iminyl radical intermediate II. In the following step, the ring-strain of cyclobutanone is released under the promotion of the imine radical, giving the C-centered radical III which is subsequently captured by the alkene. Meanwhile, the radical IV transfers an electron to [Cun+1] regenerating

Iron-catalyzed domino coupling reactions of π-systems

• Austin Pounder and
• William Tam

Beilstein J. Org. Chem. 2021, 17, 2848–2893, doi:10.3762/bjoc.17.196

• thermal conditions or through the Fe redox cycle, can abstract the aldehydic hydrogen to form the acyl radical 71. Subsequent radical addition to the alkene 68 to form 72 followed by cyclization with the nitrile affords the iminyl radical 73 which can abstract a hydrogen atom to form the more stable imine

• ) [137]. The reaction most likely involves an iminyl radical which undergoes a 5-exo-trig cyclization with the alkene to form the alkyl radical intermediate. Homolytic aromatic substitution (HAS) with the arene will afford the final functionalized product. Interestingly, electron-poor, electron-rich, and

• amine nucleophiles [139]. Following an iminyl radical-mediated intramolecular 1,5-cyclization, the subsequent alkyl radical could propagate across carbon monoxide, eventually terminating with an alkyl or aryl amine. In the following year, the Li group described an interesting radical cyclization of β,γ

Visible-light-mediated copper photocatalysis for organic syntheses

• Yajing Zhang,
• Qian Wang,
• Zongsheng Yan,
• Donglai Ma and
• Yuguang Zheng

Beilstein J. Org. Chem. 2021, 17, 2520–2542, doi:10.3762/bjoc.17.169

• –NHR]* complex C or the ground-state LnCuI–NHR species B to generate a cyclic iminyl radical 73a-A, which oxidizes the LnCuII–NHR complex D (Scheme 30, path a or b). Subsequently, radical 73a-A undergoes a β-C–C bond scission to provide the cyanoalkyl radical 73a-B, which is trapped by complex D and

Synthesis of phenanthridines via a novel photochemically-mediated cyclization and application to the synthesis of triphaeridine

• Songeziwe Ntsimango,
• Kennedy J. Ngwira,
• Moira L. Bode and
• Charles B. de Koning

Beilstein J. Org. Chem. 2021, 17, 2340–2347, doi:10.3762/bjoc.17.152

• synthesis of trisphaeridine to afford the product in four linear steps in an overall yield of 6.5% from 1-bromo-2,4,5-trimethoxybenzene. Keywords: aromatic compounds; cyclization; iminyl radical; phenanthridines; radical cation; synthesis; UV irradiation; Introduction Phenanthridine derivatives have

• intramolecular cyclization of O-acetyloximes to afford phenanthridines. (Figure 2, reaction 2) [8][9]. For these transformations, the reaction is thought to go via the transient iminyl radical [10]. More recently, Yu has reported the use of in situ-derived O-acyl oximes from benzaldehydes that when subjected to

• hypothesized that oxime 7 undergoes a homolytic cleavage of the N–O bond giving the iminyl radical 11 [14] followed by an intramolecular cyclization with concomitant expulsion of the ortho-methoxy group, liberating phenanthridine 9. To the best of our knowledge, such a reaction in which the aromatic methoxy

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• -position of the iminium ion generating an unstable iminyl radical 52•+ that is quickly quenched by the nearby carbazole to form a more stable carbazole centred radical 53•+. Rapid tautomerisation to imine 54•+ precludes the undesired back electron transfer. Single electron reduction of 54•+ by PC•– and

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• nitroimine (10, 20%), and pivalonitrile (11, 4%) [45]. The proposed scheme for the decomposition of di-tert-butyliminoxyl radical (8) is presented in Scheme 3 [35][45]. It includes formation of C–O dimer 4f followed by the fragmentation to iminyl radical 12, ketone 9, and nitric oxide. The formation of

• nitroimine 10 is explained by the interaction of oxime radical 8 with nitric oxide. Pivalonitrile (11) is presumably formed via β-scission of iminyl radical 12 (Scheme 3). During the decomposition of oxime radical 8 an EPR signal typical for a dialkyl aminoxyl radical (type I in Figure 1) was also observed

• intermediate, 4,5-dihydro-1,2,4-oxadiazole. An example of such intermediate 74 is shown in Scheme 27. Oxidative aromatization of 74 leads to 1,2,4-oxadiazole 72a (Scheme 26). The second pathway, hydrogen abstraction followed by β-scission presumably leads to iminyl radical, which forms the observed

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• fragmentation. N-aminopyridinium salts are also emerging starting materials. Iminyl radical generation Hydroxylamines have emerged as key precursors for iminyl radical generation [128]. Their redox properties can be easily tuned through the substitution pattern of the electrophore. They can be subjected to

• oximes 27.1 can be used to efficiently generate an iminyl radical in the presence of eosin Y (OD13, Scheme 27) [140]. This methodology was employed in hydroimination and iminohydroxylation cyclization reactions to give the pyrrolines 27.2. The transformation proceeds via a SET reduction of the electron

• 4ClCzIPN (OD8), obtained through fine-tuning of 4CzIPN (OD6), which are both strong oxidants and reductants [144]. In the search for a more atom-economical approach, the group of Li developed an iminyl radical formation by the N−H bond cleavage from the diarylimines 29.1 (Scheme 29) [145]. The direct

p-Pyridinyl oxime carbamates: synthesis, DNA binding, DNA photocleaving activity and theoretical photodegradation studies

• Panagiotis S. Gritzapis,
• Panayiotis C. Varras,
• Nikolaos-Panagiotis Andreou,
• Katerina R. Katsani,
• Konstantinos Dafnopoulos,
• George Psomas,
• Zisis V. Peitsinis,
• Alexandros E. Koumbis and
• Konstantina C. Fylaktakidou

Beilstein J. Org. Chem. 2020, 16, 337–350, doi:10.3762/bjoc.16.33

• . Reports involve arylaminyl radicals (ArNH∙) formed from arylhydrazones through the photoinduced cleavage of N–N single bonds (along with an iminyl radical) [48] or from benzotriazole derivatives after also a N–N single bond cleavage and nitrogen elimination [36]. It has been reported that amine-centred

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• generation of iminyl radical intermediate 31 by homolytic cleavage of the C–N bond which was followed by reductive elimination and oxidation to yield final compound 21. Inspired by the work of Wang et al. [15] who have exploited a Cu(II)-catalyst for the construction of pyrido[1,2-a]benzimidazoles Li and Xie

Cobalt-catalyzed directed C–H alkenylation of pivalophenone N–H imine with alkenyl phosphates

• Wengang Xu and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2018, 14, 709–715, doi:10.3762/bjoc.14.60

• alkenylation reaction, affording the product 3aj with an E/Z ratio of 4:1. In our previous study on the C–H alkylation and arylation of pivalophenone N–H imines, we demonstrated that the pivaloyl imine readily undergoes fragmentation into a cyano group via an iminyl radical under peroxide photolysis or copper

• of an iminyl radical from 3aa and a tert-butoxyl radical and its intramolecular addition to the cyclohexenyl group. On the basis of our previous studies on the N-arylimine-directed C–H alkenylation and the N–H imine-directed C–H alkylation/arylation [28][29], we are tempted to propose the catalytic

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

• the presence of the organic photocatalyst N-methyl-9-mesitylacridinium (17), CF3SO2Na was converted into CF3• upon visible-light irradiation. The CF3• radical reacted with the vinyl azide to give the iminyl radical 18 that was reduced by Mes-Acr• (Mes-Acr: 9-mesityl-10-methylacridinium) into the

Copper-catalyzed aerobic radical C–C bond cleavage of N–H ketimines

• Ya Lin Tnay,
• Gim Yean Ang and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2015, 11, 1933–1943, doi:10.3762/bjoc.11.209

• applications of the copper-catalyzed aerobic C–C bond fission of iminyl radical species for the synthesis of oxaspirocyclohexadienones as well as the electrophilic cyanation of Grignard reagents using the readily available pivalonitrile as a CN source. Results and Discussion We further explored the reactivity

• 1aa most likely via the corresponding iminyl radical, that undergoes radical fragmentation to afford the corresponding C-radical and carbonitrile 5a [55]. Thus, it is deduced that oxaspirocyclohexadienone 3a was formed through oxygenation of the putative C-radical. Moreover, in this transformation

• ). A proposed reaction mechanism for the formation of oxaspirocyclohexadienone 3a, alkene 4a, and p-tolunitrile (5a) are depicted in Scheme 5. Single-electron oxidation of N–H ketimine 1aa with higher valent Cu(II) species generated under the aerobic reaction conditions forms iminyl radical species A

Copper-catalyzed aerobic aliphatic C–H oxygenation with hydroperoxides

• Pei Chui Too,
• Ya Lin Tnay and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2013, 9, 1217–1225, doi:10.3762/bjoc.9.138

• oxidative sp3 C–H functionalization with predictable chemo- and regioselectivity [1][2][3][4]. To achieve this goal, we have recently utilized 1,5-H-radical shift [5][6] with iminyl radical species (N-radicals) generated under Cu-catalyzed aerobic reaction conditions, in which the resulting carbon-centered

• . Similarly, it was also revealed that the sp3 C–H oxygenation could proceed directed by the N–H ketimine moieties under Cu-catalyzed aerobic conditions via the corresponding iminyl radical species, where 1,2-diacylbenzenes and amino endoperoxides could be synthesized by C–H oxygenation of secondary and

Interplay of ortho- with spiro-cyclisation during iminyl radical closures onto arenes and heteroarenes

• Roy T. McBurney and
• John C. Walton

Beilstein J. Org. Chem. 2013, 9, 1083–1092, doi:10.3762/bjoc.9.120

• , benzofuro- or benzothieno-isoquinolines, formed at higher temperatures. Estimates by steady-state kinetic EPR established that iminyl radical cyclisations onto aromatics took place about an order of magnitude more slowly than prototypical C-centred radicals. The cyclisation energetics were investigated by

• derivatives [1][2]. Spiro-cyclisations in which tethered radicals add to the ipso-C-atoms of the rings are less common, although minor spiro-products not infrequently accompany the main ortho-ones in Pschorr syntheses [3][4][5]. Cyclisations onto arenes by N-centred radicals are rarer, but iminyl radical ArC

• research initiated spiralling interest by synthetic chemists in iminyl radical-mediated preparations. Recently iminyls have been generated from quite a variety of precursors [10][11][12][13][14][15], and their cyclisations onto arenes [16][17][18][19][20][21] and heteroarenes [22][23][24] have attracted

Some aspects of radical chemistry in the assembly of complex molecular architectures

• Béatrice Quiclet-Sire and
• Samir Z. Zard

Beilstein J. Org. Chem. 2013, 9, 557–576, doi:10.3762/bjoc.9.61

• powder in combination with acetic acid can be extended to the production of iminyls by reduction of oxime esters [72][73]. This variant allows an easy access to pyrrolenines as underscored by the synthesis of complex structure 173 from thebain-derived oxime pivalate 171 via iminyl radical 172 (Scheme 32

• agents. Radical allylations using allylic alcohol derivatives. Synthesis of variously substituted lactams. Nickel-mediated synthesis of unsaturated lactams. Total synthesis of (±)-3-demethoxy-erythratidinone. Generation and capture of an iminyl radical from an oxime ester. Acknowledgements We are