Iodine-Induced Reaction Cascades for the Rapid Construction of Variously Substituted Benzothiophenes

Domino Reaction Protocol to Synthesize Benzothiophene-Derived Chemical Entities as Potential Therapeutic Agents

An efficient synthesis of 3-amino-2-formyl-functionalized benzothiophenes by a domino reaction protocol and their use to synthesize a library of novel scaffolds have been reported. Reactions of ketones and 1,3-diones with these amino aldehyde derivatives formed a series of benzothieno[3,2-b]pyridine and 3,4-dihydro-2H-benzothiopheno[3,2-b]quinolin-1-one, respectively. A plausible mechanism for the formation of fused pyridine derivatives by the Friedlander reaction has been elucidated by density functional theory (DFT) calculations. Furthermore, hydrazones were obtained by reacting the aldehyde functional group of benzothiophenes with different hydrazine derivatives. Preliminary screening of these compounds against several bacterial strains and cancer cell lines led to the discovery of several hit molecules. Hydrazone and benzothieno[3,2-b]pyridine derivatives are potent cytotoxic and antibacterial agents, respectively. One of the potent compounds effected ∼97% growth inhibition of the LOX IMVI cell line at 10 μM concentration.

Concise synthesis and in vitro anticancer activity of benzo[g][1]benzopyrano[4,3-b]indol-6(13H)-ones (BBPIs), topoisomerase I inhibitors based on the marine alkaloid lamellarin

Benzo[g][1]benzopyrano[4,3-b]indol-6(13H)-ones (BBPIs) are potent anticancer compounds having unique BBPIs ring system designed on the basis of the marine natural product lamellarin D. In this study, we describe an alternative synthesis of a 2-demethoxy series of BBPIs, employing van Leusen pyrrole synthesis and an intramolecular Heck reaction as the key reactions. Cytotoxicity of the derivatives against several cancer and normal cell lines is reported.

Mechanochemical Synthesis of Functionalized Quinolines by Iodine Mediated Oxidative Annulation

An iodine-mediated environmentally benign synthesis of multi-substituted quinoline derivatives is developed using a solvent-free mechanochemical process. Appropriately designed and easily accessible protecting group-free aniline derivatives were used for the oxidative annulation reaction, and a series of quinoline derivatives with variable functionalities were synthesized up to 89 % isolated yield. Importantly, the activator iodine remains in the quinoline molecule and promotes further functionalizations. The present methodology is beneficial with regard to operational simplicity and mild reaction conditions.

Preparation of oxazolines and oxazoles via a PhI(OAc)2-promoted cyclization of N-propargylamides

A metal-free cyclization of N-propargylamides for the synthesis of various oxazolines and oxazoles via a 5-exo-dig process is presented. Using (diacetoxyiodo)benzene (PIDA) as a reaction promoter and lithium iodide (LiI) as an iodine source, intramolecular iodooxygenation of N-propargylamides proceeded readily, leading to the corresponding (E)-5-iodomethylene-2-oxazolines in good to excellent isolated yields. In addition, using the PhI(OAc)2/LiI system, N-propargylamides can be converted to the corresponding oxazole-5-carbaldehydes in the presence of oxygen under visible light irradiation. The resulting products can be further converted into various oxazoline and oxazole derivatives after simple derivatizations, and this method ultimately offers an efficient route to a variety of biologically active structures.

Electrophilic Cyclization Involving Carbon-Selenium/Carbon-Halide Bond Formation: Synthesis of 3-Substituted Selenophenes

The butylselanyl propargyl alcohols reacted with iodine to afford 3-iodoselenophenes. The change of nucleophile position from propargyl to homopropargyl was crucial for the aromatization and formation of selenophene rings. The experiments revealed that bromine and N-bromosuccinimide were not able to cyclize the butylselanyl propargyl alcohols; however, when the bromine source was copper(II) bromide the corresponding 3-bromoselenophenes were obtained in good yields. In addition, the reaction of butylselanyl propargyl alcohols with diorganyl diselenides catalyzed by copper(I) iodide gave the 3-(organoselanyl)selenophenes. The reaction took place with aromatic rings substituted by either electron-donating or -withdrawing groups in the alkynes and propargyl positions. The steric effects of substituents were dominant in determining the yields, whereas electronic effects had only a minor influence. Furthermore, by monitoring the reaction by ¹H NMR, we were able to identify the key intermediate, which supported the elaboration of a proposed reaction mechanism. The 3-iodoselenophenes prepared allowed the synthesis of multifunctional selenophenes via application in metal-catalyzed coupling reactions, such as Sonogashira, Ullmann and Suzuki type reactions.

Iodine(iii)-induced regioselective carbocyclization of terminal alkynes: a facile approach to prepare 1,1-diiodomethylene substituted cyclic compounds

An iodine(iii)-induced regioselective carbocyclization of functionally substituted terminal alkynes to afford 1,1-diiodomethylene substituted cyclic compounds is reported.

Recent developments in synthetic methods for benzo[b]heteroles

Benzo[b]heteroles containing heteroatoms other than nitrogen and oxygen have received considerable attention for their potential applications in materials science. This poses an increasing demand for efficient, selective, and broad-scope methods for their synthesis. This review article summarizes the recent developments in synthetic methods and approaches to access representative members of the benzoheterole family.

Iodine-mediated synthesis of heterocycles via electrophilic cyclization of alkynes

Syntheses of heterocyclesvia5-exoor 6-endo-digiodocyclizations from alkynes.

Diorganyl Dichalcogenides-Promoted Nucleophilic Closure of 1,4-Diyn-3-ols: Synthesis of 2-Benzoyl Chalcogenophenes

We report here the preparation of chalcogenophene derivatives via cyclization reactions of diynols promoted by diorganyl dichalcogenides and a halogen source. Different chalcogenophenes, such as 4-halo-selenophenes, 4-butylselenyl-selenophenes, halo-thiophenes, and 4-methylthio-thiophenes, were selectively prepared in good yields from the same starting materials. The results revealed that the halogen source had a significant effect on the proportion of 4-bromo-selenophenes and 4-butylselenyl-selenophenes. The best yields of 4-iodo-selenophenes were obtained with iodine as a halogen source, while the use of NBS gave exclusively the 4-butylselenyl-selenophenes. The experiments also revealed that the cyclization reaction to form 4-halo-thiophene derivatives can also be controlled changing the ratios of reagents. The 4-iodo-thiophenes were exclusively obtained by using dimethyl disulfide (2.0 equiv) and iodine (1.5 equiv), while the 4-bromo-thiophenes were obtained when the reaction was carried out with a 1.5 molar ratio of dimethyl disulfide and a halogen source. In addition, the reaction of diynols with an excess of dimethyl disulfide in the presence of NBS gave the 4-methylthio-thiophenes as sole products. We also studied the application of chalcogenophenes obtained as starting materials in the Suzuki, Sonogashira, and Ullmann cross-coupling reactions.

Sulfoxide-Directed Metal-Free ortho-Propargylation of Aromatics and Heteroaromatics

A sulfoxide-directed, metal-free ortho-propargylation of aromatics and heteroaromatics exploits intermolecular delivery of a propargyl nucleophile to sulfur followed by an intramolecular relay to carbon. The operationally simple cross-coupling procedure is general, regiospecific with regard to the propargyl nucleophile, and shows complete selectivity for products of ortho-propargylation over allenylation. The use of secondary propargyl silanes allows metal-free ortho-coupling to form carbon–carbon bonds between aromatic and heteroaromatic rings and secondary propargylic centres. The ‘safety-catch’ nature of the sulfoxide directing group is illustrated in a selective, iterative double cross-coupling process. The products of propargylation are versatile intermediates and they have been readily converted into substituted benzothiophenes.

Microwave-assisted synthesis of 3-aminobenzo[b]thiophene scaffolds for the preparation of kinase inhibitors

Microwave-assisted synthesis of 3-aminobenzo[b]thiophenes has been applied to 3 kinase inhibitor scaffolds.

Scaffold-divergent synthesis of ring-fused indoles, quinolines, and quinolones via iodonium-induced reaction cascades

N-(2-Iodophenyl)imines A are readily formed from Schiff's base condensation of 2-iodoanilines with carbonyls and ketals. These imines provide useful substrates in scaffold-divergent synthesis through the attachment of an alkyne (Songashira coupling or acyl substitution of a Weinreb amide) followed by an iodonium-induced reaction cascade to give ring-fused indoles B, quinolines C, or quinolones D depending on the reaction conditions employed.