Cu2O-catalyzed cascade phosphinylation/cyclization of 2'-aminochalcones for the synthesis of hemi-indigo derivatives

A Cu2O-catalyzed cascade phosphinylation/cyclization reaction of 2'-aminochalcones and diphenylphosphine oxides to produce hemi-indigo derivatives has been developed. This strategy facilitates the sequential formation of a C-P bonds and a C-N bond in a single reaction step. Notably, the approach features one-pot operation, an earth-abundant copper catalyst, readily available starting materials, a broad substrate scope and high compatibility with functional groups, providing 33 compounds in acceptable yields.

Synthesis of Indenones via Persulfate Promoted Radical Alkylation/Cyclization of Biaryl Ynones with 1,4-Dihydropyridines

The oxidative radical cascade cyclization of alkynes has emerged as a versatile strategy for the efficient construction of diverse structural units and complex molecules in organic chemistry. This work reports an alkyl radical initiated 5-exo-trig cyclization of biaryl ynones with 1,4-dihydropyridines to selectively synthesize indenones.

Characterization of the Reversible Intersystem Crossing Dynamics of Organic Photocatalysts Using Transient Absorption Spectroscopy and Time-Resolved Fluorescence Spectroscopy

Thermally activated delayed fluorescence (TADF) emitters are molecules of interest as homogeneous organic photocatalysts (OPCs) for photoredox chemistry. Here, three classes of OPC candidates are studied in dichloromethane (DCM) or N,N-dimethylformamide (DMF) solutions, using transient absorption spectroscopy and time-resolved fluorescence spectroscopy. These OPCs are benzophenones with either carbazole (2Cz-BP and 2tCz-BP) or phenoxazine/phenothiazine (2PXZ-BP and 2PTZ-BP) appended groups and the dicyanobenzene derivative 4DP-IPN. Dual lifetimes of the S1 state populations are observed, consistent with reverse intersystem crossing (RISC) and TADF emission. Example fluorescence lifetimes in DCM are (5.18 ± 0.01) ns and (6.22 ± 1.27) μs for 2Cz-BP, (1.38 ± 0.01) ns and (0.32 ± 0.01) μs for 2PXZ-BP, and (2.97 ± 0.01) ns and (62.0 ± 5.8) μs for 4DP-IPN. From ground state bleach recoveries and time-correlated single photon counting measurements, triplet quantum yields in DCM are estimated to be 0.62 ± 0.16, 0.04 ± 0.01, and 0.83 ± 0.02 for 2Cz-BP, 2PXZ-BP, and 4DP-IPN, respectively. 4DP-IPN displays similar photophysical behavior to the previously studied OPC 4Cz-IPN. Independent of the choice of solvent, 4DP-IPN, 2Cz-BP, and 2tCz-BP are shown to be TADF emitters, whereas emission by 2PXZ-BP and 2PTZ-BP depends on the molecular environment, with TADF emission enhanced in aggregates compared to monomers. Behavior of this type is representative of aggregation-induced emission luminogens (AIEgens).

Synthesis of 3-Thiocyanobenzothiophene via Difunctionalization of Active Alkyne Promoted by Electrochemical-Oxidation

A novel and green method for the synthesis of 3-thiocyanatobenzothiophenes via electrochemical-oxidation promoted difunctionalization of active alkyne has been developed. In this protocol, inexpensive and easily available potassium thiocyanate was chosen as the thiocyanation reagent, 2-alkynylthioanisoles as the substrates, a variety of 3-thiocyanatobenzothiophenes were obtained in moderate to good yields under oxidant- and catalyst-free conditions. Moreover, the continuous flow system has good applicability for this transformation, the use of continuous flow system has overcome the disadvantage of low efficiency in traditional electrochemical amplification, and realized the stable and excellent yields of target products in the scale-up reactions.

Sustainable access to benzothiophene derivatives bearing a trifluoromethyl group via a three-component domino reaction in water

A catalyst-free three-component domino reaction was developed for the synthesis of benzothiophene fused pyrrolidones bearing a CF3 group for the first time. The notable advantages of this strategy over the existing methods include the use of water as a solvent at room temperature, transition metal-free conditions, a broad substrate scope, and easy scale-up synthesis. More importantly, the benzothiophene derivatives have been found to show potent anticancer activities using the Cell Counting Kit-8 (CCK-8) assay.

Visible-light-promoted decarboxylative radical cascade cyclization to acylated benzimidazo/indolo[2,1-a]isoquinolin-6(5H)-ones in water

A metal-free visible-light-induced decarboxylative radical addition/cyclization procedure at room temperature was described for the synthesis of acylated benzimidazo/indolo[2,1-a]isoquinolines. The procedure was prepared in water via a reaction of functionalized 2-arylbenzoimidazoles or 2,3-diarylindoles and α-oxocarboxylic acids in the presence of phenyliodine(iii) diacetate (PIDA) in one step under mild reaction conditions. In this procedure, traditional heating and metal reagents could be effectively avoided to access 1,4-dicarbonyl-containing benzimidazo/indolo[2,1-a]isoquinoline-6(5H)-ones in satisfactory yields.

Visible light-mediated radical-cascade addition/cyclization of arylacrylamides with aldehydes to form quaternary oxindoles at room temperature

The visible light-induced oxidative radical cascade coupling of N-arylacrylamides with aldehydes using bromide as the hydrogen atom transfer agent to synthesize functional oxindoles is described.

Electrochemical Enabled Cascade Phosphorylation of N-H/O-H/S-H Bonds with P-H Compounds: An Efficient Access to P(O)-X Bonds

An electrochemical three component cascade phosphorylation reaction of various heteroatoms-containing nucleophiles including carbazoles, indoles, phenols, alcohols, and thiols with Ph₂ PH has been established. Electricity is used as the "traceless" oxidant and water and air are utilized as the "green" oxygen source. All kinds of structurally diverse organophosphorus compounds with P(O)-N/P(O)-O/P(O)-S bonds are assembled in moderate to excellent yields (three categories of phosphorylation products, 50 examples, up to 97 % yield). A tentative free radical course is put forward to rationalize the reaction procedure.

Visible-light-induced ligand to metal charge transfer excitation enabled phosphorylation of aryl halides

We herein described a visible light induced nickel(II)-catalyzed cross-coupling of secondary phosphine oxides with aryl halides. The Ni(I) species and chlorine atom radical Cl˙ were generated via the ligand to metal charge transfer (LMCT) process of the NiCl2(PPh3)2, which allows nickel(IV)-phosphorus species in situ formation, giving various tertiary phosphine oxides under photocatalyst-free conditions.

Photocatalytic transition-metal-free direct 3-alkylation of 2-aryl-2H-indazoles in dimethyl carbonate

A general transition-metal-free photocatalytic decarboxylative 3-alkylation reaction of 2-aryl-2H-indazoles was developed under visible-light irradiation under mild conditions.

Cascade Radical Annulation of 2-Alkynylthio(seleno)anisoles with Acetone or Acetonitrile: Synthesis of 3-Acetomethyl- or Cyanomethyl-Substituted Benzothio(seleno)phenes

An efficient method for the direct preparation of 3-aceto(cyano)methyl-substituted benzothio(seleno)phenes has been achieved through C(sp³)-H bond activation of easily available acetone or acetonitrile and cascade radical cyclization reaction. In this cascade radical cyclization reaction, C(sp²)-C(sp³) and C(sp²)-S bonds, as well as benzenethio(seleno)phene skeletons, can be built along with the cleavage of the C(sp³)-S bond, demonstrating the high step-economics and efficiency of this approach.

Nitriles as radical acceptors in radical cascade reactions

The application of the cyano group as a radical acceptor in the cascade reactions for the construction of various important heterocycles and carbocycles was summarized.

Organic thermally activated delayed fluorescence (TADF) compounds used in photocatalysis

Organic compounds that show Thermally Activated Delayed Fluorescence (TADF) have become wildly popular as next-generation emitters in organic light emitting diodes (OLEDs). Since 2016, a subset of these have found increasing use as photocatalysts. This review comprehensively highlights their potential by documenting the diversity of the reactions where an organic TADF photocatalyst can be used in lieu of a noble metal complex photocatalyst. Beyond the small number of TADF photocatalysts that have been used to date, the analysis conducted within this review reveals the wider potential of organic donor-acceptor TADF compounds as photocatalysts. A discussion of the benefits of compounds showing TADF for photocatalysis is presented, which paints a picture of a very promising future for organic photocatalyst development.

Catalyst-free generation of acyl radicals induced by visible light in water to construct C–N bonds

A new route to produce acyl radicals by the cleavage of C_sp2–C_sp2 bonds of α-diketones irradiated by visible light was developed and hydroxylamides or amides were selectively synthesized in water.

Visible-Light-Induced Phosphorylation of Imidazo-Fused Heterocycles under Metal-Free Conditions

A metal-free and base-free procedure for the phosphorylation of imidazo[1,2-a]pyridines with phosphine oxides under the irradiation of visible light at room temperature in green solvent was reported, featuring mild and sustainable conditions, convenient operation, as well as good functional group compatibility.

Hantzsch Ester-Mediated Synthesis of Phenanthridines under Visible-Light Irradiation

An efficient photocatalytic synthesis of phenanthridines mediated by an organo-photoredox initiator Hantzsch ester has been developed via denitrogenative intramolecular annulation of benzotriazolyl chalcones. The highly reducing photoactivated Hantzsch ester facilitates the transformation of benzotriazolyl chalcones into phenanthridinyl chalcones through photoinduced electron transfer (PET) and hydrogen atom transfer (HAT) processes. The mild reaction conditions utilizing inexpensive Hantzsch ester as photosensitizer, wide reaction scope and excellent functional group tolerance are notable attributes of the methodology.

K2S2O8-promoted C-Se bond formation to construct α-phenylseleno carbonyl compounds and α,β-unsaturated carbonyl compounds

A novel K₂S₂O₈-promoted C–Se bond formation from cross-coupling under neutral conditions has been developed. A variety of aldehydes and ketones react well using K₂S₂O₈ as the oxidant in the absence of catalyst and afford desired products in moderate to excellent yields. This protocol provides a very simple route for the synthesis of α-phenylseleno carbonyl compounds and α,β-unsaturated carbonyl compounds.

K₂S₂O₈-promoted C–Se bond formation from the cross-coupling of C(sp³)–H bond adjacent to carbonyl group with diphenyl diselenide under metal-free conditions.

Transition-metal-free sulfonylations of methylthiolated alkynones to synthesize 3-sulfonylated thioflavones

A set of transition-metal-free NaI/TBHP-mediated sulfonylation cyclization reactions of methylthiolated alkynones with sulfonyl hydrazides was developed, by which various 3-sulfonylated thioflavones were prepared under mild reaction conditions.

Photoinduced double [2 + 2] cycloaddition relay of yne–allenones for highly diastereoselective synthesis of hexacyclic 1-naphthols

A new photoinduced photocatalyst-free energy-transfer strategy for double [2 + 2] cycloaddition relay of yne–allenones is reported for the first time and used to produce a series of hitherto unreported hexacyclic 1-naphthols.