Reductive dimerization of benzothiazolium salts

Three different types of reaction products were obtained from the reduction of 2-substituted 3-methylbenzothiazolium salts using Na : Hg (1 wt%). Depending on the 2-substituents, two types of dimeric compounds were obtained: the 2-cyclohexyl-, 2-phenyl-, and 2-(p-tolyl)-substituted species are reduced to the corresponding 2,2'-bibenzo[d]thiazoles, while their 2-((p-OMe)C6H4)- and 2-((p-NMe2)C6H4)-substituted derivatives afford cis-[1,4]benzothiazino[3,2-b][1,4]benzothiazines. Furthermore, in the presence of molecular O2, new disulfide derivatives were obtained from the bibenzo[d]thiazoles. The products were obtained in a moderate to good yield, and the structures were confirmed using single-crystal X-ray diffraction. The electrochemistry and further reactivity towards different oxidants of the dimeric compounds were studied; the 2,2'-bibenzo[d]thiazoles show oxidation potentials similar to that of ferrocene and are converted back to the corresponding benzothiazolium cations by mild oxidants such as TCNQ. In contrast, the benzothiazino-benzothiazines show no oxidations in the solvent window of THF.

Tandem Dearomative/Rearomative (3 + 2) Annulation of Aroyl-Substituted Donor-Acceptor Cyclopropanes with Benzothiazoles

A series of benzo[d]pyrrolo[2,1-b]thiazoles was synthesized by (3 + 2) annulation of aroyl-substituted donor-acceptor cyclopropanes with benzothiazoles. The annulation, promoted by a substoichiometric amount of Sc(OTf)₃, takes place through the formation of the respective dearomatized (3 + 2) adducts, followed by unexpected decarbethoxylative and dehydrogenative rearomatization to afford fully aromatized products. The unusual reactivity is attributed to the presence of an extra aroyl group in the donor-acceptor cyclopropanes.

An efficient metal free synthesis of 2-aminobenzothiozoles - a greener approach

A facile one-pot, metal-free method for the synthesis of 2-aminobenzothiazoles was developed, which includes an initial reaction of electron-deficient 2-haloanilines with aromatic isothiocyanates and the subsequent intramolecular cyclization of the resulting thioureas through the SNAr mechanism. This one-pot, atom-economical, robust, and scalable method avoids the use of reagents such as acid chlorides and Lawesson's reagent that are difficult to handle.

1,2-Disubstituted Benzimidazoles by the Iron Catalyzed Cross-Dehydrogenative Coupling of Isomeric o-Phenylenediamine Substrates

Benzimidazoles are common in nature, medicines, and materials. Numerous strategies for preparing 2-arylbenzimidazoles exist. In this work, 1,2-disubstituted benzimidazoles were prepared from various mono- and disubstituted ortho-phenylenediamines (OPD) by iron-catalyzed oxidative coupling. Specifically, O₂ and FeCl₃·6H₂O catalyzed the cross-dehydrogenative coupling and aromatization of diarylmethyl and dialkyl benzimidazole precursors. N,N'-Disubstituted-OPD substrates were significantly more reactive than their N,N-disubstituted isomers, which appears to be relative to their propensity for complexation and charge transfer with Fe³⁺. The reaction also converted N-monosubstituted OPD substrates to 2-substituted benzimidazoles; however, electron-poor substrates produce 1,2-disubstituted benzimidazoles by intermolecular imino-transfer. Kinetic, reagent, and spectroscopic (UV-vis and EPR) studies suggest a mechanism involving metal-substrate complexation, charge transfer, and aerobic turnover, involving high-valent Fe(IV) intermediates. Overall, comparative strategies for the relatively sustainable and efficient synthesis of 1,2-disubstituted benzimidazoles are demonstrated.

Iodine mediated oxidative cross-coupling of unprotected anilines and heteroarylation of benzothiazoles with 2-methylquinoline

Iodine-promoted oxidative C-H/C-H cross-coupling of unprotected anilines and 2-methylquinoline to furnish C4-carbonylated aniline (4-aminophenyl)(quinoline-2-yl) methanones in moderate to good yields has been demonstrated. This work provides the first site-selective approach for the synthesis of free amino groups containing methanones including unprecedented C-H functionalization rather than the N-H functionalization of unprotected anilines via the Kornblum oxidation of 2-methylquinoline. Furthermore, we noticed that the incorporation of KOH under standard conditions provides 2-heteroarylbenzothiazoles from benzothiazoles and 2-methylquinoline in good to excellent yields. These transformations do not require any transition metals or peroxides and tolerate various functional groups such as methoxy, hydroxy, bromo, chloro and nitro groups. Moreover, a plausible mechanistic pathway is proposed.

Synthesis of 2-aryl-1H-Benzimidazoles and 2-aryl-1H-perimidines Using Arylidene Meldrum's Acid as a Source of the Aryl Group and Oxidant

Arylidene Meldrum's acid is employed as a source of the aryl group and oxidant for the synthesis of 2-aryl-1 H–benzimidazoles by a condensation reaction with 1,2-phenylenediamine in refluxing ethanol with good to high yields. Arylidene Meldrum's acids were also used as a source of the aryl group and oxidant for the synthesis of 2-aryl-1 H-perimidines by a condensation reaction with 1,8-diaminonaphthalene in refluxing ethanol with high yields.

Complexes of (η5-Cp*)Ir(iii) with 1-benzyl-3-phenylthio/selenomethyl-1,3-dihydrobenzoimidazole-2-thione/selenone: catalyst for oxidation and 1,2-substituted benzimidazole synthesis

The treatment of 1-benzyl-3-phenylthio/selenomethyl-1,3-dihydrobenzoimidazole-2-thione/selenone [L1-L4] with [(η⁵-Cp*)IrCl(μ-Cl)]₂ at 25 °C followed by NH₄PF₆ results in [(η⁵-Cp*)Ir(L)Cl][PF₆] (1-4 for L = L1 to L4), authenticated with high-resolution mass spectrometry (HR-MS) and multi-nuclei nuclear magnetic resonance (NMR) imaging (¹H, ¹³C{¹H} and ⁷⁷Se{¹H}). The structures of 1-4, established with single-crystal X-ray diffraction, reveal a "piano-stool" geometry around the Ir. The Ir-thio/selenoether (Ir-S/Ir-Se) bond distances (Å) are 2.347(18)-2.355(4)/2.4663(12)-2.4663(13) and Ir-thione/selenone (Ir-S/Ir-Se) distances are 2.4146(19)-2.417(2)/2.5141(16)-2.5159(12). The reaction of 1,2-phenylenediamine with benzylic alcohols and furfuryl alcohol under mild and ambient conditions, catalyzed efficiently with complexes 1-4, generates bisimine in situ. Cyclization and rearrangement via 1,3-hydride shift triggered by its electrophilic activation with Ir(iii) species finally results in 1,2-disubstituted benzimidazole. The yield of the heterocycles in this one-pot synthesis is excellent to good. The aldehydes generated in situ by aerial oxidation of alcohols in the presence of 1-4 as catalysts are precursors to the bisimine as the protocols of this heterocycle synthesis carried out in the absence of 1,2-phenylenediamine give them in excellent-to-good yield. The oxidation of alcohols by hydrogen transfer to acetone was catalyzed efficiently with complexes 1-4 and resulted in aldehyde/ketone in excellent-to-good yield. Each catalytic process is marginally more efficient with 1 than its counterparts.

The synthesis of benzimidazoles via a recycled palladium catalysed hydrogen transfer under mild conditions

An efficient synthesis of benzimidazoles was developed by virtue of a recycled palladium catalyzed hydrogen transfer.

Lithium Hexamethyldisilazane Transformation of Transiently Protected 4-Aza/Benzimidazole Nitriles to Amidines and their Dimethyl Sulfoxide Mediated Imidazole Ring Formation

Trimethylsilyl-transient protection successfully allowed the use of lithium hexamethyldisilazane to prepare benzimidazole (BI) and 4-azabenzimidazole (azaBI) amidines from nitriles in 58-88% yields. This strategy offers a much better choice to prepare BI/azaBI amidines than the lengthy, low-yielding Pinner reaction. Synthesis of aza/benzimidazole rings from aromatic diamines and aldehydes was affected in dimethyl sulfoxide in 10-15 min, while known procedures require long time and purification. These methods are important for the BI/azaBI-based drug industry and for developing specific DNA binders for expanded therapeutic applications.

Introduction to Microelectrode Arrays, the Site-Selective Functionalization of Electrode Surfaces, and the Real-Time Detection of Binding Events

Microelectrode arrays have great potential as analytical tools because currents can be independently measured at each electrode in the array. In principle, these currents can be monitored in order to follow in real time the binding events that occur between the members of a molecular library and a biological target. To capitalize on this potential, the surface of the array must be selectively functionalized so that each unique member of the molecular library is associated with a unique individually addressable electrode or set of electrodes in the array. To this end, this instructional review summarizes methods for coating the arrays with porous polymers that allow for the attachment of molecules to the surface of the array, selectively conducting reactions at individual electrodes in the array, characterizing molecules that are placed on the arrays, and running the analytical experiments needed to monitor in real time binding events between molecules on the array and a biological target.

Expedient synthesis of benzimidazoles using amides

In the present report an efficient, rapid, facile and inexpensive route for the synthesis of benzimidazoles using 1,2-arylenediamines and amides in acidic medium under thermal/microwave conditions is developed.