Cu(I)-Catalyzed Synthesis of [60]Fullerene-Fused Lactams and Further Electrochemical Functionalization

Functionalization of [C60]-Fullerene: A Recent Update

Functionalization of fullerene has garnered great attention owing to its unique structural, electronic, and photophysical properties. The distinctive properties of fullerene derivatives make them a multifaceted candidate for application in photochemical, biological, nanomaterial, and photophysical studies. The radical scavenging properties of fullerene owe them an important role in reactive oxygen species (ROS) capturing applications. The organic photovoltaic cells are fabricated utilizing functionalized fullerenes due to its electron-accepting properties. The increased prominence of functionalization led to different innovative methodologies to bloom. The present review focuses on various synthetic strategies were adopted for [C60]-annulation reactions to accomplish carbo- and heterocycles fused fullerenes from early 2014 to till date.

Synthesis of [60]fullerene-fused dihydroindolizines via copper-catalyzed dearomative N-heteroannulation

A novel copper-catalyzed approach for the construction of [60]fullerene-fused dihydroindolizine derivatives has been developed through dearomative N-heteroannulation of [60]fullerene with electron-withdrawing group-substituted 2-picolines. A plausible reaction mechanism has been proposed. Additionally, a representative fullerene product can be applied in organic solar cells as the third component.

Tether-Directed Electrosynthesis of Bicyclic [60]Fullerene Derivatives Fused with 5-Membered Azacycle and 13-Membered Carbocycle

Tether-directed electrosynthesis of [60]fullerene derivatives fused with 5-membered azacycle and 13-membered carbocycle, that is, bicyclic 1,4,9,12- and 1,2,4,15-adducts, has been achieved unexpectedly for the first time. The novel bicyclic [60]fullerene derivatives are obtained by the electrochemical reduction of [60]fullerene-fused indolines or lactams and subsequent regioselective cyclization with 2,2″-bis(bromomethyl)-1,1':3',1″-terphenyl. The product structures have been characterized by spectroscopic data and single-crystal X-ray analysis.

Copper-Catalyzed N-Heteroannulation of [60]Fullerene with Aryl Sulfonamides and Paraformaldehyde: Synthesis and Functionalization of [60]Fullerene-Fused Imidazolidines

The Cu(II)-catalyzed N-heteroannulation reaction of [60]fullerene (C60) with aryl sulfonamides and paraformaldehyde has been disclosed for the synthesis of diverse C60-fused imidazolidines, of which one or both of the ArSO2 moieties could be removed selectively. Further transformations into the unexpected bicyclic 1,2,3,4-adduct and C60-fused imidazolidinium iodide salt have also been demonstrated. A plausible reaction mechanism is proposed on the basis of control experiments. C60-fused imidazolidinium iodide has been employed as an additive in the PC61BM layer of inverted planar perovskite solar cells to increase power conversion efficiency.

KOtBu-Promoted [3 + 2] Cycloaddition of Dimethyl Sulfoxide with Fullerenes

KOtBu-promoted [3 + 2] cycloaddition of dimethyl sulfoxide (DMSO) with fullerenes has been developed for facile and efficient one-pot synthesis of 1,2,3,4-cyclic sulfoxide-fused [60]/[70]fullerene dihydrides, which offers a versatile platform for the site-selective preparation of various fullerene multiadducts with a wide range of functional groups. The utility of these tetra-functionalized fullerenes is demonstrated by the successful application as electron-transport materials in perovskite solar cells.

Base-Promoted 1,4-Difunctionalization of [60]Fullerene with H-Phosphonates and Alkyl Bromides

The DBU-promoted three-component coupling reaction of H-phosphonates, [60]fullerene, and alkyl bromides has been developed as a facile and efficient protocol for the one-pot synthesis of various 1,4-(phosphonyl)(organo)[60]fullerenes. This method exhibits high regioselectivity at the 1,4-position on the [60]fullerene core and features a metal-free nature, easy operation, low cost, and a wide range of substrates.

α-Halocarbonyls as a Valuable Functionalized Tertiary Alkyl Source

This review introduces the synthetic organic chemical value of α-bromocarbonyl compounds with tertiary carbons. This α-bromocarbonyl compound with a tertiary carbon has been used primarily only as a radical initiator in atom transfer radical polymerization (ATRP) reactions. However, with the recent development of photo-radical reactions (around 2010), research on the use of α-bromocarbonyl compounds as tertiary alkyl radical precursors became popular (around 2012). As more examples were reported, α-bromocarbonyl compounds were studied not only as radicals but also for their applications in organometallic and ionic reactions. That is, α-bromocarbonyl compounds act as nucleophiles as well as electrophiles. The carbonyl group of α-bromocarbonyl compounds is also attractive because it allows the skeleton to be converted after the reaction, and it is being applied to total synthesis. In our survey until 2022, α-bromocarbonyl compounds can be used to perform a full range of reactions necessary for organic synthesis, including multi-component reactions, cross-coupling, substitution, cyclization, rearrangement, stereospecific reactions, asymmetric reactions. α-Bromocarbonyl compounds have created a new trend in tertiary alkylation, which until then had limited reaction patterns in organic synthesis. This review focuses on how α-bromocarbonyl compounds can be used in synthetic organic chemistry.

NHC catalyzed radical tandem cyclization: an efficient synthesis of α,α-difluoro-γ-lactam derivatives

Herein, an N-heterocyclic carbene (NHC) catalyzed radical tandem cyclization reaction of N-allylbromodifluoroacetamides and aldehydes has been developed. This method is an efficient protocol for synthesizing α,α-difluoro-γ-lactam derivatives in moderate to good yields (27 examples, up to 88% yield and 10 : 1 dr). This strategy features mild and metal-free conditions, high efficiency, and a broad substrate scope.

Catalytic System-Controlled Regioselective 1,2- and 1,4-Carboannulations of [60]Fullerene

Selective functionalization of fullerenes is an important but challenging topic in fullerene chemistry and synthetic chemistry. Here we present the first example of catalytic system-controlled regioselective 1,2- and 1,4-addition reactions for the flexible and efficient synthesis of novel 1,2- and 1,4-carbocycle-fused fullerenes via a palladium-catalyzed decarboxylative carboannulation process.

A regioselective step-by-step C60Cl6 functionalization approach affords a novel family of C60Ar5Th'Th''H fullerene derivatives with promising antiviral properties

We report a novel reaction of the recently discovered family of fullerene derivatives C₁-C₆₀Ar₅Th' with thiophene derivatives Th''H yielding a previously unknown family of C₁-C₆₀Ar₅Th'Th''H compounds with three different types of functional aromatic addends attached to the carbon cage. The discovered reaction paves a way to the synthesis of novel C₆₀ fullerene derivatives with promising antioxidant and antiviral properties.

[60]Fullerene-Fused Cyclopentanes: Mechanosynthesis and Photovoltaic Application

The mechanochemical cascade reaction of [60]fullerene with 3-benzylidene succinimides, diethyl 2-benzylidene succinate, or 2-benzylidene succinonitrile in the presence of an inorganic base has been investigated under solvent-free and ball-milling conditions. This protocol provides an expedient method to afford various [60]fullerene-fused cyclopentanes, showing advantages of good substrate scope, short reaction time, and solvent-free and ambient reaction conditions. Furthermore, representative fullerene products have been applied in inverted planar perovskite solar cells as efficient cathode interlayers.

Electrochemical Palladium‐Catalyzed Oxidative Carbonylation‐Cyclization of Enallenols

Herein, we report an electrochemical oxidative palladium-catalyzed carbonylation-carbocyclization of enallenols to afford γ-lactones and spirolactones, which proceeds with excellent chemoselectivity. Interestingly, electrocatalysis was found to have an accelerating effect on the rate of the tandem process, leading to a more efficient reaction than that under chemical redox conditions.

Electrosynthesis of Decorated Basket Molecules: [60]Fullerene-Fused 12-Membered Macrolactones

The electrosynthesis of decorated basket molecules, that is, [60]fullerene-fused 12-membered macrolactones, has been achieved efficiently for the first time by the electrochemical reduction of [60]fullerene-fused 6-membered lactones and subsequent ring expansion with 1,2-bis(1-bromoalkyl)benzenes. The observed isomeric distributions of the obtained macrolactones are elucidated by theoretical calculations. The product structures have been firmly established by single-crystal X-ray analyses.

Electrochemically Promoted Benzylation of [60]Fullerooxazolidinone

Benzylation of the electrochemically generated dianion from N-p-tolyl-[60]fullerooxazolidinone with benzyl bromide provides three products with different addition patterns. The product distribution can be dramatically altered by varying the reaction conditions. Based on spectral characterizations, these products have been assigned as mono-benzylated 1,4-adduct and bis-benzylated 1,2,3,16- and 1,4,9,25-adducts, respectively. The assigned 1,2,3,16-adduct has been further established by X-ray diffraction analysis. It is believed that the 1,4-adduct is obtained by decarboxylative benzylation of the dianionic species, while bis-benzylated 1,2,3,16- and 1,4,9,25-adducts are achieved via a rearrangement process. In addition, the electrochemical properties of these products have been studied.

Copper-mediated synthesis of fullerooxazoles from [60]fullerene and N-hydroxybenzimidoyl cyanides

A novel and efficient copper-mediated [3 + 2] heteroannulation reaction of [60]fullerene with N-hydroxybenzimidoyl cyanides has been developed for the synthesis of fullerooxazoles. A possible reaction mechanism involving unique C-CN and N-OH bond cleavages and subsequent C-OH bond formation for N-hydroxybenzimidoyl cyanides is proposed to explain the generation of fullerooxazoles. In addition, the formed fullerooxazoles can be further electrochemically transformed into amidated 1,2-hydrofullerenes.

Isocyanide-Induced Annulation Leading to Cyclopento-, Methano-, and Cyclopentano-[60]Fullerene Derivatives

The three-component annulation reactions of C₆₀, alkyl isocyanide, and dimethyl acetylenedicarboxylate (DMAD) or unsymmetric alkynes are investigated to afford cyclopent-2-en-1-imino- and ketenimine methano-[60]fullerene derivatives, which, upon hydration in the presence of acid, yield the corresponding fullerene amides. Dimethyl 2,3-pentadienedioate, the allene counterpart of DMAD, and ethyl buta-2,3-dienoate undergo four-component annulation with C₆₀, alkyl isocyanide, and water under similar conditions to yield cyclopentano-[60]fullerene derivatives with similar amide groups.

Transition metal-catalyzed organic reactions in undivided electrochemical cells

Transition metal-catalyzed organic electrochemistry is a rapidly growing research area owing in part to the ability of metal catalysts to alter the selectivity of a given transformation. This conversion mainly focuses on transition metal-catalyzed anodic oxidation and cathodic reduction and great progress has been achieved in both areas. Typically, only one of the half-cell reactions is involved in the organic reaction while a sacrificial reaction occurs at the counter electrode, which is inherently wasteful since one electrode is not being used productively. Recently, transition metal-catalyzed paired electrolysis that makes use of both anodic oxidation and cathodic reduction has attracted much attention. This perspective highlights the recent progress of each type of electrochemical reaction and relatively focuses on the transition metal-catalyzed paired electrolysis, showcasing that electrochemical reactions involving transition metal catalysis have advantages over conventional reactions in terms of controlling the reaction activity and selectivity and figuring out that transition metal-catalyzed paired electrolysis is an important direction of organic electrochemistry in the future and offers numerous opportunities for new and improved organic reaction methods.

One-pot, three-component regioselective coupling reaction of triphenylamine/carbazole derivatives with [60]fullerene and indoles via an “umpolung relay” strategy

An “umpolung relay” three-component regioselective coupling reaction of triphenylamine/carbazole derivatives with C60 and indoles was developed, which features high regioselectivity, broad substrate scope, and excellent functional group tolerance.