Deciphering Co(III)-Catalyzed Oxidative C-H/C-H Annulation Towards Maleimide-Fused Imidazopyridine AEEgens.

A cobalt(III)-catalyzed dual C(sp)-H/C(sp)-H activation of 2-arylimidazopyridines and its annulation with N-substituted maleimides leads to polycyclic aromatic heterocycles. This sustainable oxidative annulation uses earth-abundant, less toxic, and cost-effective cobalt(III) catalyst that complement expensive 2nd and 3rd-row metals. This oxidative annulation features a broad substrate scope with very good functional group tolerance.

Solvent Dictated Organic Transformations.

Solvent plays an important role in many chemical reactions. The C-H activation has been one of the most powerful tools in organic synthesis. These reactions are often assisted by solvents which not only provide a medium for the chemical reactions but also facilitate reaching to the product stage.

Electron-donor-acceptor (EDA) complex-driven regioselective vicinal and oxidative geminal functionalization of alkynes.

A visible-light-initiated electron-donor-acceptor (EDA) complex-driven regioselective vicinal and oxidative geminal thiosulfonylation of alkynes is presented. Organic thiosulfonates act as an acceptor, producing either sulfonyl (RSO˙) or thiyl (RS˙) radicals under base and solvent switchable conditions. Simultaneous installation of three different functionalities, carbonyl, sulfonyl, and thiyl, takes place under one condition, while another condition leads to vicinal thiolation and sulfonylation.

Harnessing reductive BF-complexation Ru(II)-catalyzed N-O cleavage of isoxazoles.

Developed here is a highly fluorescent organic N,O bidentate BF complex from isoxazole in the presence of a Ru(II) catalyst. Herein, the complexation proceeds a selective N-O cleavage of the isoxazole ring. The complex shows absorption () in the range of 352-363 nm with an extinction coefficient () in the range of 8000-64 000 M cm, and fluorescence emission () in the range of 413-485 nm with a Stokes shift of 61-125 nm having quantum yield up to 33%.

Iodine-Promoted Sulfoximidation of Cinnamic Acids via Oxidative C═C Bond Cleavage.

An iodine-promoted C═C bond cleavage with concomitant decarboxylation and cross-coupling between cinnamic acids and -sulfoximines has been developed. This reaction proceeds via selective C═C bond cleavage, followed by decarboxylation and oxidative sulfoximidation. This metal- and base-free protocol involves dioxygen as the source of oxygen, which is facilitated by -butyl hydroperoxide (TBHP) as the oxidant affording -aroylated sulfoximines with good functional group tolerance and good yields.

Electrochemical NH-Sulfoximidation with α-Keto Acids.

An electrochemical N-acylation of sulfoximine has been achieved via the coupling of α-keto acids and NH-sulfoximines. This process involves the sequential cleavage of C-C bond followed by C(sp)-N bond formation, with the liberation of H and CO as the by-products. A library of N-aroylated sulfoximines is produced via the coupling of aroyl and sulfoximidoyl radicals by anodic oxidation under constant current electrolysis (CCE).

Photo-Induced Generation of Oxygenated Quaternary Centers via EnT Enabled Singlet O Addition to C3-Maleimidated Quinoxaline: A Reagent-Less Approach.

Demonstrated here is an external photo-sensitizer-free (auto-sensitized) singlet oxygen-enabled solvent-dependent tertiary hydroxylation and aryl-alkyl spiro-etherification of C3-maleimidated quinoxalines. Such "reagent-less" photo-oxygenation at Csp-H and etherification involving Csp-H/Csp-H are unparalleled. Possibly, the highly π-conjugated N-H tautomer allows the substrate to get excited by irradiation, and subsequently, it attains the triplet state via ISC.

Isothiocyanates: happy-go-lucky reagents in organic synthesis.

Owing to their unique structural features, isothiocyanates (ITCs) are a class of highly useful and inimitable reagents as the -NCS group serves both as electrophile and nucleophile in organic synthesis. ITCs share a rich legacy in organic, medicinal, and combinatorial chemistry. Compared to their oxygen equivalents, isocyanates, ITCs are easily available, less unpleasant, and somewhat less harmful to work with (mild conditions) which makes them happy-go-lucky reagents.

PIDA/I-mediated photo-induced aerobic -acylation of sulfoximines with methylarenes.

A visible-light-promoted, PIDA/I-mediated acylation of NH-sulfoximines with methylarenes as an acyl source has been achieved. This transition metal and photosensitizer-free approach provides easy access to -acylsulfoximines oxidative coupling of sulfoximines with easily available methylarenes without using any peroxide source. Mechanistic investigations suggest the intermediacy of radicals and the importance of molecular oxygen.

Access to Chromenopyrrole via Tandem [3 + 2] Cycloaddition and Intramolecular C-O Coupling.

A mild and concise method for the synthesis of chromenopyrrole from 2'-hydroxychalcone is devised. The reaction proceeds via an initial [3 + 2] cycloaddition on the C═C bond of 2'-hydroxychalcone and 1,3-dipolarophile, generated in situ by the reaction of ethyl isocyanoacetate and AgOAc. This is then followed by an intramolecular C-O bond formation with the -OH group and C5-H of the in situ generated pyrrole, leading to chromenopyrroles.

Base-Promoted Synthesis of -Arylisothiazolones via Intramolecular Dehydrative Cyclization of α-Keto--acylsulfoximines.

A base (EtN)-promoted synthesis of 1,4-diarylisothiazolones from α-keto--acylsulfoximines has been achieved. The reaction proceeds via α-hydrogen abstraction from sulfoximine, followed by an intramolecular nucleophilic attack at the keto carbonyl to form a -hydroxy isothiazolone intermediate. The 1,4-substituted isothiazolone is obtained after dehydration via an E1cB path.

Pd(II)-Catalyzed Three-Component Synthesis of Furo[2,3-]pyrimidines from β-Ketodinitriles, Boronic Acids, and Aldehydes.

A Pd(II)-catalyzed three-component synthesis of 2,4,6-triarylfuro[2,3-]pyrimidines from β-ketodinitriles, boronic acids, and aldehydes has been developed. The participation of both nitrile (-CN) groups led to the concurrent construction of furo-pyrimidine via the formation of C-C, C═C, C-O, C-N, and C═N bonds. The compounds show excellent photoluminescence properties with absorption maxima ranging from 348 to 387 nm and emission from 468 to 533 nm.

Electrochemical N-Aroylation of Sulfoximines by Using Benzoyl Hydrazines with H Generation.

Developed here is a robust electrochemical cross-coupling reaction between aroyl hydrazine and NH-sulfoximine via concomitant cleavage and formation of C(sp )-N bonds with the evolution of H and N as innocuous by-products. This sustainable protocol avoids the use of toxic reagents and occurs at room temperature. The reaction proceeds via the generation of an aroyl and a sulfoximidoyl radical via anodic oxidation under constant current electrolysis (CCE), affording N-aroylated sulfoximine.

Base-Induced Decarboxylative 1,1-Alkoxy Thiolation via Hydrothiolation of Vinylene Carbonate.

A base-mediated 1,1-difunctionalization of vinylene carbonate has been achieved using two different nucleophiles, namely, thiol and alcohol, with the assistance of air (O). In alcoholic solvents, decarboxylation occurs at room temperature to provide a 1,1-difunctionalized product, where vinylene carbonate serves as an ethynol (C2) synthon in this three-component reaction. On the other hand, in acetonitrile, exclusive hydrothiolation occurs under the basic conditions at room temperature.

Photo-induced 1,2-thiohydroxylation of maleimide involving disulfide and singlet oxygen.

A visible light-driven di-functionalization of maleimide with disulfide and -generated singlet oxygen offers selective 1,2-thiohydroxylation under additive-free conditions. Here the disulfide plays the dual role of photosensitizer and the coupling reagent. Notably, the hydroxyl functionality originates from the generated singlet oxygen followed by HAT from HO (moisture).

Isoxazole as a nitrile synthon: to the -alkenylated isoxazole and benzonitrile with allyl sulfone catalyzed by Ru(II).

A Ru(II) catalyzed regioselective Heck-type C-H olefination of isoxazole with unactivated allyl phenyl sulfone is revealed. The solvent DCM offers dual sp-sp C-H activation an -directed strategy, leading to -olefinated isoxazoles with exclusive -selectivity. On the other hand, in DCE solvent, isoxazole serves as the nitrile synthon and leads to -olefinated benzonitrile.

Synthesis of Chromenopyrroles (Azacoumestans) from Functionalized Enones and Alkyl Isocyanoacetates.

Elegant synthetic strategies for chromenopyrroles (azacoumestans) have been devised via cycloaddition of 2-hydroxychalcone/cyclic enones and alkyl isocyanoacetate, followed by lactonization. Herein, ethyl isocyanoacetate acts as a C-NH-C-C═O synthon contrary to its hitherto applications as a C-NH-C synthon. Subsequently, pentacyclic-fused pyrroles were also constructed from the -iodo benzoyl chromenopyrroles using the Pd(II) catalyst.

Visible-light driven electron-donor-acceptor (EDA) complex-initiated synthesis of thio-functionalized pyridines.

A visible/solar-light-induced electron-donor-acceptor (EDA)-aggregated/mediated radical cyclization between ()-2-(1,3-diarylallylidene)malononitriles and thiophenols leads to poly-functionalized pyridines. The two reacting partners form an EDA complex that absorbs light and triggers the single-electron transfer (SET) to generate a thiol radical, which undergoes addition/cyclization with dicyanodiene through the formation of C-S and C-N bonds.

Mn(I)-Catalyzed Preferential Electrophilic C3-Maleimidation in Quinoxaline Leading to Spirocyclization and Dehydrogenation of Succinimides.

A Mn(I)-catalyzed site-selective nondirected C3-maleimidation of quinoxaline is established. Herein, the electrophilic C3-metalation precedes over the -directed strategy to access diversely substituted quinoxaline-appended succinimides. The products undergo PIFA-promoted C(sp)-C(sp) spirocyclization via π-electrons drifting from aryls and Selectfluor-mediated dehydrogenation of succinimide at room temperature.

NIS-initiated photo-induced oxidative decarboxylative sulfoximidation of cinnamic acids.

-Iodosuccinimide catalyzed, visible-light-induced oxidative decarboxylative cross-coupling between cinnamic acids and NH-sulfoximines is presented. This strategy results in the formation of α-keto--acyl sulfoximines the construction of two new CO bonds and one C-N bond. The -generated -iodosulfoximine serves as the light-absorbing species in the absence of any external photosensitizer.

Dearomative bis-functionalization of quinoxalines and bis--arylation of (benz)imidazoles Cu(II)-mediated addition of boronic acids.

A Cu(OTf)-mediated regioselective dearomative aryl-hydroxylation across the C(sp)N bond of 2-aryl quinoxalines and bis--arylation of (benz)imidazoles were developed using aryl boronic acids. For the dearomative aryl-hydroxylation, the C-center should be electrophilic ( 0.08), the N-center nucleophilic ( -0.

Visible/solar-light-driven thiyl-radical-triggered synthesis of multi-substituted pyridines.

A light-triggered synthesis of thio-functionalized pyridines is demonstrated using γ-ketodinitriles, thiols, and eosin Y as the photocatalyst. The reaction proceeds the selective attack on one of the cyano groups by an generated thiyl radical. The reaction also proceeds with nearly equal efficiency using direct sunlight.

Visible-Light-Mediated Solvent-Switched Photosensitizer-Free Synthesis of Polyfunctionalized Quinolines and Pyridines.

A solvent (2,2,2-trifluoroethanol (TFE) vs ethyl alcohol (EtOH)) switched synthesis of quinolines and pyridines is illustrated from ()-2-(1,3-diphenylallylidene)malononitriles via a Pd(II)-catalyzed photochemical process. The active catalyst [LPd(0)] generated serves as an exogenous photosensitizer. The process offers predominantly -alkenylated quinolines and pyridines in TFE and EtOH, respectively.

Transformable Transient Directing Group-Assisted C(sp)-H Activation: Synthesis and Late-Stage Functionalizations of -Alkenylanilines.

The isocyanate group in aryl isocyanates serves as a transformable transient directing group in a Ru(II)-catalyzed olefination leading to -alkenylanilines. In alcoholic solvents, aryl isocyanates are transformed into carbamates, which initiate the insertion of acrylates via -C-H activation. In particular, AmOH serves the dual role of solvent-cum transient directing mediator.