Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

• interconnected photocatalytic cycles as the hydrodehalogenation, an aryl radical 2• is formed via successive PET and C(sp2)–X bond cleavage (Figure 17B). Carbon monoxide, introduced to the reaction mixture by a tube-in-tube reactor, traps the aryl radical to generate the acyl radical 23 (Figure 17B

• ). Nucleophilic addition of the amine to the acyl radical and amine-assisted intermolecular proton transfer [84] generates the α-hydroxy radical 24 from which formation of the amide 25 proceeds either via i) oxidation by [Ir2]+ and deprotonation or ii) radical chain propagation [85]. Electron-deficient, electron

Rapid gas–liquid reaction in flow. Continuous synthesis and production of cyclohexene oxide

• Kyoko Mandai,
• Tetsuya Yamamoto,
• Hiroki Mandai and
• Aiichiro Nagaki

Beilstein J. Org. Chem. 2022, 18, 660–668, doi:10.3762/bjoc.18.67

• residence time was elongated, leading to a significant decrease in the yield of cyclohexene oxide (Supporting Information File 1, Figure S2) [32]. Overall, we assume that, in our flow system, the highly efficient contact of acyl radical 5 with oxygen during the autoxidation of aldehyde could produce the

DABCO-promoted photocatalytic C–H functionalization of aldehydes

• Bruno Maia da Silva Santos,
• Mariana dos Santos Dupim,
• Cauê Paula de Souza,
• Thiago Messias Cardozo and
• Fernanda Gadini Finelli

Beilstein J. Org. Chem. 2021, 17, 2959–2967, doi:10.3762/bjoc.17.205

• amines (Table 1, entries 9 and 10 and Supporting Information File 1, Scheme S2). Radical trapping experiments with TEMPO also showed a radical path mechanism, and the acyl radical was detected as an intermediate (Supporting Information File 1, Table S4). The absence of product formation in the Giese

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

• conditions, both primary and secondary alcohols are oxidized to the corresponding aldehyde/ketone, so the chronology of the addition remains unclear whether the reaction proceeds exclusively via an alkyl radical followed by subsequent oxidation, an acyl radical, or a combination of both. Further, slight

• 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

• electronic properties of the alkenes to control the chronology of the additions. The rate of addition of the acyl radical to an electro-deficient alkene is about three times greater than that of a styrene derivative [109][110]. The electrophilic radical, adjacent to an EWG, will favor the subsequent addition

Synthesis of highly substituted fluorenones via metal-free TBHP-promoted oxidative cyclization of 2-(aminomethyl)biphenyls. Application to the total synthesis of nobilone

• Ilya A. P. Jourjine,
• Lukas Zeisel,
• Jürgen Krauß and
• Franz Bracher

Beilstein J. Org. Chem. 2021, 17, 2668–2679, doi:10.3762/bjoc.17.181

• cyclization. From aldehyde 2l an acyl radical should subsequently be formed, for which cyclization reactions with heteroarenes and benzenoids are well documented [67][68]. Aldehyde 2l may also be further oxidized to give carboxylic acid B instead. With the oxidant of choice, aqueous TBHP, however, aldehyde 2l

• cyclic lactones [69]. The intramolecular cyclization of the acyl radical A gives the tricyclic radical species C, which then forms fluorenone (3) after abstraction of a hydrogen radical by an additional equivalent of the tert-butoxy radical. Conclusion In summary, we have demonstrated that the metal-free

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

A complementary approach to conjugated N-acyliminium formation through photoredox-catalyzed intermolecular radical addition to allenamides and allencarbamates

• Olusesan K. Koleoso,
• Matthew Turner,
• Felix Plasser and
• Marc C. Kimber

Beilstein J. Org. Chem. 2020, 16, 1983–1990, doi:10.3762/bjoc.16.165

• examining the full mechanism of this transformation, expanding the scope of substrates that can be used in the radical addition step, and alternative fates for the α-N-acyl radical 13 [58][59][60]. Electrophilic activation of allenamides. The planned intramolecular radical addition to allenamides generating

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

• activation step to produce a palladacyclic intermediate. In parallel, the oxidative decarboxylation of the α-ketoacid induced by the photocatalyst in its excited state generates the corresponding acyl radical. The latter is intercepted by the palladacycle, leading to a Pd(III) species. Remarkably, the

• . Furthermore, a peroxide (TBHP) is needed to oxidize the Ir-based photoredox catalyst and to generate the acyl radical via hydrogen atom transfer. From the mechanistic perspective this synergistic dual catalytic system merging C–H activation and photocatalysis is similar to the one described by Sanford for the

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

• , oxylacyl, and carbamoyl radicals and their analogues The photocatalyzed generation of acyl radicals is of great interest as they are precursors for the synthesis of diverse carbonyl compounds [88]. The acyl radical is generally considered as a nucleophilic radical and reacts rapidly with electron-poor π

• responsible for the H atom abstraction from the α-keto acid. The α-keto carboxyl radical undergoes a decarboxylation, leading to the desired acyl radical. Acyl radicals can also be accessed through the oxidative cleavage of a redox-active group, such as acylsilanes or 1,4-dihydropyridine derivatives. In 2018

• , Fagnoni and co-workers developed an organophotocatalytic method to access nonsymmetrical ketones through the oxidation of the alkyl acylsilanes 18.1 (Eox ≈ +1.3 V) by an acridinium photocatalyst OD2 (E(PC+*/PC) ≈ 2.1 V, Scheme 18) [90]. After the fragmentation, the acyl radical can add to various Michael

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• the aldehyde 161 could afford the acyl radical 168 through a HAT process, which then could add to diethyl maleate (154) and afford the desired product 162 through a propagation mechanism. In 2019, König and co-workers presented a catalytic arylation of aromatic aldehydes 170 by aryl bromides 171 using

• of the benzophenone 172 to the triplet state 173 by UV irradiation, followed by HAT from the aldehyde 170 to 173 and the formation of the acyl radical 175. At the same time, the nickel(0) complex 176 performs an oxidative addition reaction to the aryl bromide 171, and the nickel(II) complex 177

• formed reacts with an acyl radical 175 to give the nickel(III) complex 178, which could then undergo a reductive elimination reaction to furnish the desired ground state benzophenone product 172. The nickel(0) catalyst can then be regenerated by SET (Scheme 41). However, they suggested that the first

Vicinal difunctionalization of alkenes by four-component radical cascade reaction of xanthogenates, alkenes, CO, and sulfonyl oxime ethers

• Shuhei Sumino,
• Takahide Fukuyama,
• Mika Sasano,
• Ilhyong Ryu,
• Antoine Jacquet,
• Frédéric Robert and
• Yannick Landais

Beilstein J. Org. Chem. 2019, 15, 1822–1828, doi:10.3762/bjoc.15.176

• CO to give an acyl radical C [35], which then adds to electron-deficient sulfonyl oxime ether 3a to afford 5a. The resulting radical D then undergoes β-fragmentation providing 5a along with the phenylsulfonyl radical E. SH2 reaction between radical E and hexabutylditin regenerates the tributyltin

• radical which sustains the radical chain. Since radical B can also add to sulfonyl oxime ether 3a, we used high CO pressure conditions to encourage the radical carbonylation to form acyl radical C. Conclusion In summary, we demonstrated that a four-component radical cascade reaction, between xanthogenates

Oxidative radical ring-opening/cyclization of cyclopropane derivatives

• Yu Liu,
• Qiao-Lin Wang,
• Zan Chen,
• Cong-Shan Zhou,
• Bi-Quan Xiong,
• Pan-Liang Zhang,
• Chang-An Yang and
• Quan Zhou

Beilstein J. Org. Chem. 2019, 15, 256–278, doi:10.3762/bjoc.15.23

• -rich aryl groups could deliver higher yields than that with electron-deficient ones. As outlined in Scheme 12, a tert-butoxy radical and a methyl radical were generated from cleavage of DTBP at the reaction temperature. Aldehyde 48 is easily transformed into acyl radical 50 in the presence of an alkoxy

• radical or a methyl radical [74][75][76][77]. The acyl radical 50 adds to the C–C double bond of MCPs giving the benzyl radical intermediate 51. The ring-opening of radical intermediate 51 occurres to form the alkyl radical intermediate 52 which intermolecularly cyclizes with the aryl ring. The following

Unprecedented nucleophile-promoted 1,7-S or Se shift reactions under Pummerer reaction conditions of 4-alkenyl-3-sulfinylmethylpyrroles

• Takashi Go,
• Akane Morimatsu,
• Hiroaki Wasada,
• Genzoh Tanabe,
• Osamu Muraoka,
• Yoshiharu Sawada and
• Mitsuhiro Yoshimatsu

Beilstein J. Org. Chem. 2018, 14, 2722–2729, doi:10.3762/bjoc.14.250

• rearrangement of 6,7-dihydroindol-4(5H)-ones. However, after implementing this approach, an undesirable isomer was obtained [21]. Although a number of acid- [22][23] and metal-catalysed cascade processes [24][25] have been developed (for example, Pictet–Spengler [26] and Ugi-type reactions [27], the acyl

• radical cyclisations [28] and the 1,7-electrocyclisation of azomethine ylides or ring expansion sequences [29]), most of these approaches are ineffective for synthesising pyrrolo[3,2-c]azepines. Recently, Echavarren and Beller reported a novel Au- or Pt-catalysed cycloisomerisation reaction of pyrrole-2

Investigations of alkynylbenziodoxole derivatives for radical alkynylations in photoredox catalysis

• Yue Pan,
• Kunfang Jia,
• Yali Chen and
• Yiyun Chen

Beilstein J. Org. Chem. 2018, 14, 1215–1221, doi:10.3762/bjoc.14.103

• to study the radical acceptor and oxidative quencher reactivity of alkynylbenziodoxoles, in which unsubstituted alkynylbenziodoxoles played balancing roles in both processes, while electron-rich benziodoxole derivatives demonstrate synthetic advantages in some cases. Keywords: acyl radical; alkyl

• investigate their reactivity toward alkyl radical and acyl radical additions in photoredox catalysis. The mechanistic investigations were carried out to study the derivatization of BI-alkynes in radical acceptor and oxidative quencher reactivity, and the electron-rich benziodoxole derivatives demonstrated

• then tested the secondary alkyl radical precursor 6b and observed 74% yield of alkyne 5b using unsubstituted BI-alkyne 3c. In contrast, 3,4-dimethoxy BI'-alkyne 3f gave improved 80% yields of 5b. We finally moved to test the BI-alkyne derivatives toward acyl radical additions (Scheme 5). With ketoacid

Visible-light-induced, Ir-catalyzed reactions of N-methyl-N-((trimethylsilyl)methyl)aniline with cyclic α,β-unsaturated carbonyl compounds

• Dominik Lenhart and
• Thorsten Bach

Beilstein J. Org. Chem. 2014, 10, 890–896, doi:10.3762/bjoc.10.86

• could occur by hydrogen transfer to the starting material, i.e., the α,β-unsaturated carbonyl compound [39], which would explain why the yields never exceeded 50%. Upon hydrogen transfer the α,β-unsaturated carbonyl compound would give a cyclic α-acyl radical, which would be capable to re-oxidize the

Efficient carbon-Ferrier rearrangement on glycals mediated by ceric ammonium nitrate: Application to the synthesis of 2-deoxy-2-amino-C-glycoside

• Alafia A. Ansari,
• Y. Suman Reddy and
• Yashwant D. Vankar

Beilstein J. Org. Chem. 2014, 10, 300–306, doi:10.3762/bjoc.10.27

• position so that the C-allyl pseudoglycoside is fomed. However, we were not able to isolate Me3SiOAc. As the acetate ion and the acetyl radical are better leaving groups the formation of the acyl radical seems to be more facile than the formation of the alkoxy radicals (e.g., benzyloxy and methoxy). This

Damage of polyesters by the atmospheric free radical oxidant NO₃^•: a product study involving model systems

• Catrin Goeschen and
• Uta Wille

Beilstein J. Org. Chem. 2013, 9, 1907–1916, doi:10.3762/bjoc.9.225

• confirmed through independent control experiments. Oxidation of aldehyde 5 to the carboxylic acid 6 under the experimental conditions could by initiated through abstraction of the aldehyde hydrogen atom by NO3• [29], followed by trapping of the resulting acyl radical 10 by NO3• to give the mixed anhydride

A construction of 4,4-spirocyclic γ-lactams by tandem radical cyclization with carbon monoxide

• Mitsuhiro Ueda,
• Yoshitaka Uenoyama,
• Nozomi Terasoma,
• Shoko Doi,
• Shoji Kobayashi,
• Ilhyong Ryu and
• John A. Murphy

Beilstein J. Org. Chem. 2013, 9, 1340–1345, doi:10.3762/bjoc.9.151

• -lactams in which CO was introduced as the lactam carbonyl moiety [17][18][19][20][21][22][23]. Our approach consists of a sequence of aryl radical cyclization, radical carbonylation [24][25][26][27], and spirocyclization of the resulting acyl radical onto an azide group, which can give 4,4-spirocyclic γ

• radical A gives an alkyl radical B, which adds to CO to give an acyl radical C. Finally, the 5-exo addition of acyl radical C onto an azide group takes place with the liberation of dinitrogen to give a cyclized amidyl radical D [29][30], which abstracts hydrogen from TTMSS, affording the 4,4-spirocyclic

Exploration of an epoxidation–ring-opening strategy for the synthesis of lyconadin A and discovery of an unexpected Payne rearrangement

• Brad M. Loertscher,
• Yu Zhang and
• Steven L. Castle

Beilstein J. Org. Chem. 2013, 9, 1179–1184, doi:10.3762/bjoc.9.132

• efficiently furnish its bicyclo[5.4.0]undecane system, which is shown in bold in Figure 1. Subsequent to this observation, we performed model studies that demonstrated the viability of highly stereoselective 7-exo-trig acyl radical–6-exo-trig alkyl radical cyclizations as a means of preparing bicyclo[5.4.0

Radical carbonylations using a continuous microflow system

• Takahide Fukuyama,
• Md. Taifur Rahman,
• Naoya Kamata and
• Ilhyong Ryu

Beilstein J. Org. Chem. 2009, 5, No. 34, doi:10.3762/bjoc.5.34

• acyl radical traps (entries 6 and 7 ). Gratifyingly, in both cases, good yields of the three-component coupling products were formed by using reduced CO pressure. Conclusion We have developed a facile platform to conduct radical carbonylation under CO pressure in a flow system comprised of a T-shaped

Part 3. Triethylborane- air: a suitable initiator for intermolecular radical additions of S-2-oxoalkyl- thionocarbonates (S-xanthates) to olefins

• Jean Boivin and
• Van Tai Nguyen

Beilstein J. Org. Chem. 2007, 3, No. 47, doi:10.1186/1860-5397-3-47

• ][10][11][12][13][14] Trapping with benzaldehyde gave aldol 1d (48%, Scheme 1) and thus confirmed that a boron enolate is a plausible intermediate in the reduction of compound 1a into 1b. One cannot put aside the possibility that the reduction of the transient α-acyl radical may also occur, to a minor

• in which Et3B is implicated not only in the generation of the α-acyl radical but also in the reaction with the latter, in a stoichiometric manner, to afford an intermediate boron enolate. Lowering the amount of Et3B would therefore minimise the premature unwanted reduction. This hypothesis was then

• to stabilised radical B. The latter fragments either to xanthate A and Et• or, more easily, to stabilised α-acyl radical C and dithiocarbonate D. From the intermediate radical C, three possible routes determine the outcome of the reaction. Route a1 represents the xanthate group transfer between

Do α-acyloxy and α-alkoxycarbonyloxy radicals fragment to form acyl and alkoxycarbonyl radicals?

• Dennis P. Curran and
• Tiffany R. Turner

Beilstein J. Org. Chem. 2006, 2, No. 10, doi:10.1186/1860-5397-2-10

• fragmentation of radical 13a to release an acyl radical 16a. However, the ratios of 15/14a do not fit well with the standard model of competing unimolecular (fragmentation) and bimolecular (reduction) reactions in Figure 4. For example, the 10-fold dilution in going from entry 4 to entry 5 should have resulted