Visible-light-induced regioselective cross-dehydrogenative coupling of 2-isothiocyanatonaphthalenes with amines using molecular oxygen

Visible-light-induced three-component reactions of α-diazoesters, quinazolinones and cyclic ethers toward quinazoline-based hybrids

An effective approach for the construction of 4-short-chain ether attached carbonyl group-substituted quinazolines was developed. Visible-light-induced three-component reactions of α-diazoesters, quinazolinones, and cyclic ethers, with a broad substrate scope and excellent functional group tolerance, under extremely mild conditions without the need for any additional additives and catalysts, selectively led to quinazoline-based hybrids in good to excellent yields. The synthesized hybrids, which are a conglomeration of a quinazoline, a short-chain ether, and a carbonyl group in one molecular skeleton, have potential for application in the development of new drugs or drug candidates.

Visible-Light-Promoted Cascade Coupling of 2-Isocyanonaphthalenes with Elemental Sulfur and Amines to Construct Naphtho[2,1-d]thiazol-2-Amines

A visible-light-induced strategy has been explored for the synthesis of naphtho[2,1-d]thiazol-2-amines through ortho-C-H sulfuration of 2-isocyanonaphthalenes with elemental sulfur and amines under external photocatalyst-free conditions. This three-component reaction, which utilizes elemental sulfur as the odorless sulfur source, molecular oxygen as the clean oxidant, and visible light as the clean energy source, provides a mild and efficient approach to construct a series of naphtho[2,1-d]thiazol-2-amines. Preliminary mechanistic studies indicated that visible-light-promoted photoexcitation of reaction intermediates consisting of thioureas and DBU might be involved in this transformation.

Electro-oxidative three-component cascade coupling of isocyanides with elemental sulfur and amines for the synthesis of 2-aminobenzothiazoles

2-Aminobenzothiazoles are commonly encountered in various functional compounds. Herein, we disclose an electro-oxidative three-component reaction for the effective synthesis of 2-aminobenzothiazoles under mild conditions, utilizing non-toxic and abundant elemental sulfur as the sulfur source. Both aliphatic amines and aryl amines demonstrate good compatibility at room temperature, highlighting the broad functional group tolerance of this approach. Additionally, elemental selenium demonstrated reactivities comparable to those of elemental sulfur.

Base-promoted one-pot three-component desulphurization cross-coupling access to 4-cyanoimidazole

A novel, straightforward, and scalable base-mediated one-pot three-component desulphurization cross-coupling strategy is reported for the synthesis of 4-cyanoimidazole derivatives. Over 35 examples are provided and achieved yields exceeding 85%. Notably, the majority of these readily available compounds can be isolated through simple filtration, thereby circumventing the need for laborious column chromatography. Besides, the present protocol can be scaled up to 10 mmol with a yield of 87%, demonstrating promising potential for industrial applications.

Visible-Light Copper Catalysis for the Synthesis of α-Alkyl-Acetophenones by the Radical-Type Ring Opening of Sulfonium Salts and Oxidative Alkylation of Alkenes

Direct difunctionalization of simple alkenes has been treated as a powerful synthetic strategy for the construction of highly functionalized skeletons. In this study, direct oxidative coupling of sulfonium salts with alkenes was achieved under mild conditions by a blue-light-driven photoredox process using a copper complex as a photosensitizer. This protocol allows regioselective synthesis of aryl/alkyl ketones from simple sulfonium salts and aromatic alkenes via selective C-S bond cleavage of sulfonium salts and oxidative alkylation of aromatic alkenes using dimethyl sulfoxide (DMSO) as a mild oxidant.

Visible-Light-Initiated Multicomponent Reactions of α-Diazoesters to Access Organophosphorus Compounds

A simple visible-light-initiated strategy has been established for the construction of organophosphorus compounds via aerobic multicomponent reaction of α-diazoesters, cyclic ethers, and P(O)H compounds under air. A number of phosphonates and phosphinates could be efficiently isolated in moderate to good yields without the use of photosensitizers and metal reagents. This multicomponent reaction has advantages of mild condition, simple operation, eco-friendly energy, good functional-group tolerance, and gram-scale synthesis.

Domino Synthesis of Thiazolo-Fused Six- and Seven-Membered Nitrogen Heterocycles via Intramolecular Heteroannulation of In-Situ-Generated 2-(Het)aryl-4-amino-5-functionalized Thiazoles

Synthesis of novel 2-(het)aryl-substituted thiazolo-fused six- and seven-membered heterocycles, such as thiazolo[4,5-b]pyridin-5(4H)-ones, thiazolo[4,5-c]isoquinolin-5(4H)-ones, thiazolo[4,5-b]quinolin-9(4H)-ones, 4H-benzo[e]thiazolo[4,5-b]azepine-5,10-diones, have been developed in a single-pot operation via intramolecular heteroannulation of in-situ-generated 2-(het)aryl-4-amino-5-functionalized thiazoles. These 4-amino-5-functionalized thiazoles were readily obtained in a one-pot process by treatment of a range of (het)aryldithioesters with cyanamide in the presence of NaH, followed by in situ S-alkylation-intramolecular condensations of the resulting thioimidate salts with appropriate activated methylene halides. On the other hand, the corresponding 4H-benzo[b]thiazolo[4,5-e][1,4]diazepin-10(9H)-ones were synthesized in a two-step process, requiring prior isolation of 5-carboethoxy-4-(2-nitrophenyl)aminothiazoles and their subsequent reductive cyclization. The activated methylene halides employed in these reactions for the synthesis of various thiazolo-fused heterocycles were methyl bromocrotonate, ethyl 2-(bromomethyl)benzoate, 2-fluorophenacyl bromides, ethyl 2-(2-bromoacetyl)benzoate, and ethyl bromoacetate. Several of these thiazolo-fused heterocycles display yellow green to green fluorescence, and their absorption and emission spectra have also been examined.

Current Perspective of Synthesis of Medicinally Relevant Benzothiazole Based Molecules: Potential for Antimicrobial and Anti-Inflammatory Activities

The therapeutic potential of the majority of the marketed drugs is due to the presence of a heterocyclic nucleus, which constitutes a huge role in the field of medicinal chemistry. These heterocyclic scaffolds could act as a template in order to design potential therapeutic agents against several diseases. Benzothiazole scaffold is one of the influential heteroaromatic rings in the field of medicinal chemistry owing to its extensive pharmacological features. Herein, we have focused on the synthesis of benzothiazole based medicinal molecules, which possess antimicrobial and anti-inflammatory activities. This review covers a systematic description of synthetic routes for biologically relevant benzothiazole derivatives in the last five years. The main aim of this study is to show the diversification of benzothiazole based molecules into their pharmacologically more active derivatives. This review's synthetic protocols include metal-free, metal-catalyzed, and metal precursor azo dyes strategies for the development of benzothiazole derived bioactive compounds. The discussion under the various headings covers synthetic schemes and biological activities of the most potent molecules in the form of minimum inhibitory concentration.

Visible-Light Photosynthesis of CHF2 /CClF2 /CBrF2 -Substituted Ring-fused Quinazolinones in Dimethyl Carbonate

With eco-friendly and sustainable CO₂ -derived dimethyl carbonate as the sole solvent, the visible-light-induced cascade radical reactions have been established as a green and efficient tool for constructing various CHF₂ /CClF₂ /CBrF₂ -substituted ring-fused quinazolinones.

Metal-free visible-light-induced multi-component reactions of α-diazoesters leading to S-alkyl dithiocarbamates

A metal-free and visible-light-promoted strategy has been developed for the synthesis of S-alkyl dithiocarbamates through multicomponent reactions of α-diazoesters, amines and CS2.

A desulphurization strategy for Sonogashira couplings by visible light/copper catalysis

We have developed a new copper-based photocatalyst, [(binap)(tpy)Cu]Cl, and applied it in the visible-light promoted Sonogashira coupling reactions.

Visible-Light-Promoted Denitrogenative Ortho-selenylation Reaction of benzotriazinones: Synthesis of ortho-selenylated Benzamides, Ebselen Analogs

A visible-light-promoted regioselective denitrogenative cross-coupling between benzotriazinones and selenosulfonates is reported. This protocol allows for the convenient synthesis of ortho-selenylated benzamides in good yields from readily available starting materials under...

Alkylsulfonium salts for the photochemical desulphurizative functionalization of heteroarenes

A metal-free organic photoredox-catalyzed alkylation of heteroarenes using alkylsulfonium salts as alkylation reagents has been developed.

K2S2O8-mediated acylarylation of unactivated alkenes via acyl radical addition/C–H annulation cascade of N-allyl-indoles with silver cocatalysis

A silver-catalyzed, K2S2O8-mediated protocol to access the regioselective acylarylation of unactivated alkenes was reported.

C–H benzylation of quinoxalin-2(1H)-ones via visible-light riboflavin photocatalysis

An efficient visible light promoted riboflavin-catalyzed direct benzylation of substituted quinoxalin-2(1H)-ones for the synthesis of various C3-benzylated quinoxalin-2(1H)-one derivatives has been developed under mild conditions.

Visible-light-mediated multi-component carbene transfer reactions of α-diazoesters to construct multisubstituted pyrazoles and 1,3-dicarbonyl derivatives

A visible-light-promoted strategy has been developed for the assembly of multisubstituted pyrazoles and 1,3-dicarbonyl derivatives via a multi-component carbene transfer reaction of α-diazoesters.

Metal-Free Photosynthesis of Alkylated Benzimidazo[2,1-a]isoquinoline-6(5H)-ones and Indolo[2,1-a]isoquinolin-6(5H)-ones in PEG-200

A visible-light-induced decarboxylation reaction was developed for the synthesis of alkylated benzimidazo[2,1-a]isoquinoline-6(5H)-ones and indolo[2,1-a]isoquinolin-6(5H)-ones under metal-free conditions. Impressively, metal catalysts and traditionally volatile organic solvents could be effectively avoided.

Visible Light Mediated Photocatalyst Free C-S Cross Coupling: Domino Synthesis of Thiochromane Derivatives via Photoinduced Electron Transfer

An efficient visible light mediated photocatalyst free C-S cross-coupling reaction has been developed for the synthesis of thiochromane derivatives through photoinduced electron transfer (PET). This methodology was further utilized for the synthesis of thiochroman-4-ol through intermolecular three-component cross-coupling reaction. The reaction proceeds via C-S bond formation through EDA complex/thioester cleavage/inter-or intramolecular sulfa-Michael addition followed by aldol reaction sequence. The EDA complex formation between aryl iodides and xanthate has been substantiated using spectroscopic experiments and DFT calculations.

Acyl Radicals from α-Keto Acids: Metal-Free Visible-Light-Promoted Acylation of Heterocycles

A general and metal-free visible-light-induced decarboxylative arylation procedure at room temperature was described for the construction of acylated heterocyclic derivatives, such as benzimidazo/indolo[2,1-a]isoquinolin-6(5H)-ones, aroylazaspiro[4.5]trienones, thioflavones, and so on. This practical arylation procedure was conducted by using 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) as a photocatalyst under mild conditions, which avoided the use of an additional base, traditional heating, and metal reagents.

Photocatalyst- and Transition-Metal-Free Visible-Light-Promoted Intramolecular C(sp2)-S Formation

A photocatalyst- and transition-metal-free visible-light-induced cyclization of ortho-halothiobenzanilides has been developed. Upon irradiation with visible light, substrates undergo dehalogenative cyclization to 2-aryl benzothiazoles with high efficiency and selectivity. This photocyclization exhibits a high tolerance to various functional groups, is applicable for the synthesis of 2-alkyl benzothiazoles, and is easy to set up for gram-scale reaction.