Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field

• Elena R. Lopat’eva,
• Igor B. Krylov,
• Dmitry A. Lapshin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2022, 18, 1672–1695, doi:10.3762/bjoc.18.179

• aimed at overviewing the current state-of-art and perspectives of oxidative organocatalysis by redox-active molecules with the emphasis on challenging chemo-, regio- and stereoselective CH-functionalization processes. The catalytic systems based on N-oxyl radicals, amines, thiols, oxaziridines, ketone

• /peroxide, quinones, and iodine(I/III) compounds are the most developed catalyst types which are covered here. Keywords: CH-functionalization; free radicals; hypervalent iodine; N-oxyl radicals; redox-active molecules; Introduction Organocatalysis can be defined as catalysis by small organic molecules

• classified according to the catalytically active species or key intermediates: N-oxyl radicals, oxoammonium cations, amine cation radicals, thiyl radicals, quinones, dioxiranes and oxaziridines, hypervalent iodine compounds, etc. However, some examples of organocatalyzed oxidative processes, in which an

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

• Igor B. Krylov Stanislav A. Paveliev Alexander S. Budnikov Alexander O. Terent'ev N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky Prospect 47, Moscow, 119991, Russia 10.3762/bjoc.16.107 Abstract N-Oxyl radicals (compounds with an N–O• fragment) represent one

• 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

• 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

Copper catalysis with redox-active ligands

• Agnideep Das,
• Yufeng Ren,
• Cheriehan Hessin and
• Marine Desage-El Murr

Beilstein J. Org. Chem. 2020, 16, 858–870, doi:10.3762/bjoc.16.77

• with TEMPO (2,2,6,6-tetramethyl-1-piperidine N-oxyl) [25] and ABNO (9-azabicyclo[3.3.1]nonane N-oxyl) radicals [26]. Later reports enlarged the synthetic scope of this methodology and provided access to a wide range of synthetically useful building blocks such as substituted heterocycles, fluorinated

Selective benzylic C–H monooxygenation mediated by iodine oxides

• Kelsey B. LaMartina,
• Haley K. Kuck,
• Linda S. Oglesbee,
• Asma Al-Odaini and
• Nicholas C. Boaz

Beilstein J. Org. Chem. 2019, 15, 602–609, doi:10.3762/bjoc.15.55

• dyes and transition metal complexes, hypohalous acids, and persulfate anions [12][34][35][36][37][38][39][40]. An important class of catalyzed benzylic C–H to C–O transformations are those catalyzed by N-oxyl radicals. Specifically, N-oxyl radical catalysts based upon the N-hydroxyphthalimide (NHPI

Hypervalent iodine compounds for anti-Markovnikov-type iodo-oxyimidation of vinylarenes

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Mikhail A. Syroeshkin,
• Alexander A. Korlyukov,
• Pavel V. Dorovatovskii,
• Yan V. Zubavichus,
• Gennady I. Nikishin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2018, 14, 2146–2155, doi:10.3762/bjoc.14.188

• . It was shown that the iodine atom in the prepared iodo-oxyimides can be substituted by various nucleophiles. Keywords: free radicals; hypervalent iodine; imide-N-oxyl radicals; iodination; N-hydroxyimides; oxidative functionalization; Introduction The presented work opens a new chapter in the

• chemistry of N-hydroxyimides in combination with hypervalent iodine compounds with formation of imide-N-oxyl radicals. These radicals were used as reagents for the addition to a terminal position of the double bond of styrenes with subsequent iodination of the resulting benzylic radical. It is important to

• electrochemical synthesis [2], and as mediators of living polymerization [10][11]. In organic synthesis more stable types of N-oxyl radicals can be used as carbon-centered radical scavengers [12], oxidation catalysts, mainly for conversion of alcohols to carbonyl compounds [11][13][14][15][16][17]. Less stable

Cross-dehydrogenative coupling for the intermolecular C–O bond formation

• Igor B. Krylov,
• Vera A. Vil’ and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2015, 11, 92–146, doi:10.3762/bjoc.11.13

• reagents. The formation of N-oxyl radicals 212 and 207 from oximes and N-hydroxyimides was confirmed by ESR spectroscopy [197][198]. The oxidative coupling of 1,3-dicarbonyl compounds [199] and their hetero analogues [200] 213 with tert-butyl hydroperoxides catalyzed by transition metal salts (Cu, Fe, Co

• the presence of oxidants based on manganese, cobalt, and cerium [197]. The best results were achieved with the use of Mn(OAc)3 and the Co(OAc)2(cat)/KMnO4 system (Scheme 43). The yields of products 206 were as high as 94%. It is supposed that the oxidant serves two functions: the generation of N-oxyl

• radicals 207 from N-hydroxyimides or N-hydroxyamides 204 and the one-electron oxidation of 1,3-dicarbonyl compounds via the formation of complex 208. Apparently, the oxidative coupling of 1,3-dicarbonyl compounds 209 with oximes 210 occurs via a similar mechanism [198]. The reaction takes place in the

Metal-free aerobic oxidations mediated by N-hydroxyphthalimide. A concise review

• Lucio Melone and
• Carlo Punta

Beilstein J. Org. Chem. 2013, 9, 1296–1310, doi:10.3762/bjoc.9.146

• laccase-ABTS follows an electron transfer (ET) mechanism, NHPI, VLA, HBT, and NHAmediators promote a hydrogen atom transfer (HAT) route through the formation of the corresponding N-oxyl radicals as NHDs-Medox species (Scheme 11). The same research group also emphasized the specialization of mediators

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

• weak bond-dissociation enthalpies (i.e., tertiary alkyl C–H bonds, benzylic C–H bonds, etc.), by phthalimide N-oxyl radicals generated oxidatively from N-hydroxyphthalimide (NHPI), has been reported [20][21][22]. The resulting C-radicals could be trapped with molecular oxygen to form hydroperoxides. It