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The formyl C−H thiolation of aldehydes using thiosulfonates and the decatungstate anion as a photocatalyst is reported. Using this photocatalytic protocol together with a CO atmosphere, both aromatic and aliphatic thioesters can be synthesized in good yields. The transformation consists of a cascade of double SH2 reactions, HAT and an ArS group transfer. CO atmosphere effectively limits the extent of decarbonylation of acyl radicals that are generated in the reaction. [ABSTRACT FROM AUTHOR]

A new way to form fluorenones via the direct excitation of substrates instead of photocatalyst to activate the C(sp2)−H bond under redox‐neutral condition is reported. Our design relies on the photoexcited aromatic aldehyde intermediates that can be intercepted by cobaloxime catalyst through single electron transfer for following β‐H elimination. The generation of acyl radical and successful interception by a metal catalyst cobaloxime avoid the use of a photocatalyst and stoichiometric external oxidants, affording a series of highly substituted fluorenones, including six‐membered ketones, such as xanthone and thioxanthone derivatives in good to excellent yields, and with hydrogen as the only byproduct. This catalytic system features a readily available metal catalyst, mild reaction conditions and broad substrate scope, in which sunlight reaction and scale‐up experiments by continuous‐flow approach make the new methodology sustainable and amenable for potentially operational procedures. [ABSTRACT FROM AUTHOR]

In this review, we highlighted the main achievements in the field of electrocatalytic generation of acyl radicals and their applications. These electrochemical strategies were introduced with an emphasis on the substrate scope, reaction limitation and underlying mechanism. The related reactions were categorized according to the pathways of acyl radical generation, including outer‐sphere electron transfer (ET), inner‐sphere ET, and hydrogen atom transfer (HAT) processes. [ABSTRACT FROM AUTHOR]

An intramolecular hydroacylation of olefins using carboxylic acids (CAs) has been developed. With the aid of a boronic acid, CAs can be used as acyl‐radical precursors in catalytic photoredox reactions driven by visible light. The CAs are easily converted into their corresponding cyclic ketones without the need to use any stoichiometric activating reagents. Mechanistic studies implied that the formation of an "ate" complex from the CA and boronic acid is crucial for the generation of the acyl radical equivalent from the unreactive carboxy group. [ABSTRACT FROM AUTHOR]

A visible‐light‐induced cascade radical cyclization of aroyl chlorides with 2‐(allyloxy)‐benzaldehyde derivatives has been developed. The method takes advantages of unactivated C=C bonds as the acyl radical acceptors and offers a mild and green approach for the synthesis of 1,4‐diketones bearing biologically important chroman‐4‐one skeletons with moderate to good yields. [ABSTRACT FROM AUTHOR]

Abstract: A photoredox‐mediated acylation reaction of electron deficient heteroarenes with terminal alkynes is reported. The method relies on oxidative cleavage of phenylacetylenes for generation of acyl radicals as a key enabling feature. The reaction is regioselective with broad substrate scope. Quantum yield investigations support a radical chain mechanism. [ABSTRACT FROM AUTHOR]

A highly efficient and straightforward approach for the synthesis of spiroepoxy chroman-4-one derivatives was developed using a visible light-enabled tandem radical strategy. The reaction is initiated by the formation of an acyl radical that undergoes intramolecular radical cyclization and epoxidation. The optimal result was obtained with 1 mol% of Ru(bpy)3Cl2⋅6H2O, TBHP, and K2CO3 in i-PrOAc at room temperature with irradiation from a blue LED. This unprecedented tandem approach utilizes a broad range of substrates, and provides a convenient and powerful synthetic tool for accessing the synthetically useful spiroepoxy chroman-4-ones and their nitrogen-containing derivatives. [ABSTRACT FROM AUTHOR]

Glyoxal is a key compound involved in glyoxal oxidase (GLOX)-dependent production of glyoxylate, oxalate and H2O2 by lignin-degrading basidiomycetes. In this paper, we report that glyoxal was produced from a metabolite of ligninolytic fungi, linoleic acid, by manganese peroxidase (MnP)-dependent lipid peroxidation. In the absence of the parent substrate of linoleic acid, the dialdehyde was oxidized by MnP and Mn(III) chelate to start free radical reactions with emission of chemiluminescence at 700–710 nm. The spectroscopic profile of the light emission is distinguishable from (a) singlet oxygen, (b) triplet carbonyls from dioxetane and α-hydroxyperoxyl radicals, and (c) biacyl triplet formed by the coupling of two acyl radicals. The photon emission of glyoxal by MnP was activated by co-oxidation of tartrate. The MnP-dependent oxidation of glyoxal in tartrate buffers continued for 10 days without addition of exogenous H2O2. The importance of these results is discussed in relation to the free radical chemistry of lignin biodegradation by wood rot fungi. [ABSTRACT FROM AUTHOR]

Lipid peroxidation by managanese peroxidase (MnP) is reported to decompose recalcitrant polycyclic aromatic hydrocabon (PAH) and nonphenolic lignin models. To elucidate the oxidative process, linoleic acid and 13(S)-hydroperoxy-9Z,11E-octadecadienoic acid [13(S)-HPODE] were reacted with MnPs from Ceriporiopsis subvermispora and Bjerkandera adusta and the free radicals produced were analyzed by ESR. When the MnPs were reacted with 13(S)-HPODE in the presence of Mn(II), H2O2 and tert-nitrosobutane (t-NB), the ESR spectrum contained a sharp triplet of acyl radical (aN = 0.81 mT). Formation of acyl radical was also observed in the reactions of Mn(III)-tartrate with 13(S)-HPODE and with linoleic acid, but the latter reaction occurred explosively after an induction period of around 30 min. Reactions of MnP with linoleic acid in the presence of Mn(II), H2O2 and t-NB gave no spin adducts while addition of t-NB after preincubation of linoleic acid with MnP/Mn(II)/H2O2 for 2 h gave spin adducts of carbon-centered (aN = 1.53 mT, aH = 0.21 mT) and acyl (aN = 0.81 mT) radicals. In contrast to linoleic acid, methyl linoleate and oleic acid were not peroxidized by MnP and chelated Mn(III) within a few hours, indicating that structures containing both the 1,4-pentadienyl moiety and a free carboxyl group are necessary for inducing the peroxidation in a short reaction time. These results indicate that MnP-dependent lipid peroxidation is not initiated by direct abstraction of hydrogen from the bis-allylic position during turnover but proceeds by a Mn(III)-dependent hydrogen abstraction from enols and subsequent propagation reactions involving the formation of acyl radical from lipid hydroperoxide. This finding expands the role of chelated Mn(III) from a phenol oxidant to a strong generator of free radicals from lipids and lipid hydroperoxides in lignin biodegradation. [ABSTRACT FROM AUTHOR]

In this account, we describe our recent developments on the four‐types of hypervalent iodine(III)‐mediated radical reactions in organic synthesis. Firstly, the activation of aldehydic C−H bonds can be successfully effected with hypervalent iodine(III) reagents, thereby allowing the synthesis of various ketones with high efficiency. Secondly, the site‐selective oxidation of unactivated C(sp3)−H bonds of hydrocarbon substrates was realized with designer hypervalent iodine(III) reagents. Thirdly, various perfluoroalkyl and α‐aminoalkyl radicals can be generated from sodium perfluoroalkanesulfinates and sodium α‐aminoalkanesulfinates, respectively, under the influence of hypervalent iodine(III) reagents. Finally, the efficient generation of difluoromethyl radical from hypervalent difluoroacetoxyliodine(III) reagent was realized by photolysis. These four different strategies are illustrated by using various selective radical approaches. [ABSTRACT FROM AUTHOR]

The inside cover picture, provided by Sungwoo Hong and co ‐ workers, illustrates a highly efficient and straightforward approach for the synthesis of spiroepoxy chroman ‐ 4 ‐ one derivatives with light irradiation using a blue LED under mild reaction conditions. During the reaction, the aldehyde generated in situ from the benzyl alcohol could further undergo visible light ‐ mediated internal radical cyclization and epoxidation, allowing the rapid generation of valuable and synthetically useful spiroepoxy chroman ‐ 4 ‐ ones and their nitrogen ‐ containing derivatives. Details of this work can be found in the communication on pages 3945 – 3949 (S. Jung, J. Kim, S. Hong, Adv. Synth. Catal. 2017, 359, 3945 – 3949; DOI: 10.1002/adsc.201701072). [ABSTRACT FROM AUTHOR]