Tandem regioselective synthesis of tetrazoles and related heterocycles using iodine

Visible Light Mediated Co-Catalyzed Isocyanide Insertion with Sulfonyl Azide: Synthesis of Sulfonyl Carbamimidic Azide and Sulfonyl Aminotetrazole via Carbodiimide Intermediate

Herein, we report an operationally simple and efficient protocol to prepare sulfonyl carbamimidic azide and N-sulfonyl aminotetrazole via Co-catalyzed three component coupling of sulfonyl azide (acts as nitrene source), isocyanide, and TMS-azide at room temperature under visible light. Initially, the carbamimidic azide is formed, which cyclizes only in the presence of base to deliver N-sulfonyl aminotetrazole in very good yields. The sulfonyl aminotetrazole can also be synthesized directly without isolating the carbamimidic azide in the presence of base. The sulfonyl azide is anticipated to generate nitrene and reacts with isocyanide to produce carbodiimide. Subsequent addition of azide (TMS-N3 ) to carbodiimide results in the formation of carbamimidic azide.

N-Iodosuccinimide-Promoted [3 + 2] Annulation Reaction of Aryldiazonium Salts with Guanidines To Construct Aminotetrazoles

A N-iodosuccinimide (NIS)-promoted [3 + 2] annulation reaction of aryldiazonium salts with guanidines has been developed for the construction of previously elusive 2-aryl-5-amino-2H-tetrazoles. This transformation takes advantage of readily available starting materials, proceeds under metal-free, mild, and robust conditions, and holds broad functional group compatibility. The utility of this protocol is further manifested via coupling, annulation, deamination, and denitrogenation derivatizations.

Controlling Pd-Catalyzed N-Arylation and Dimroth Rearrangement in the Synthesis of N,1-Diaryl-1H-tetrazol-5-amines

The Pd-catalyzed N-arylation method for the synthesis of eighteen N,1-diaryl-1H-tetrazol-5-amine derivatives is reported. By running the reactions at 35 °C, compounds were isolated as single isomers since the undesired Dimroth rearrangement was completely suppressed. Furthermore, the Dimroth rearrangement of N,1-diaryl-1H-tetrazol-5-amines was rationalized by conducting comprehensive experiments and NMR analysis as well as density functional theory (DFT) calculations of thermodynamic stability of the compounds. It was established that the Dimroth rearrangement is thermodynamically controlled, and the equilibrium of the reaction is determined by the stability of the corresponding isomers. The mechanism was investigated by additional DFT calculations, and the opening of the tetrazole ring was shown to be the rate-determining step. By maneuvering Pd-catalyzed N-arylation and the subsequent Dimroth rearrangement, two more N,1-diaryl-1H-tetrazol-5-amine derivatives were acquired, which otherwise cannot be synthesized by employing the C-N cross-coupling reaction.

A more sustainable isothiocyanate synthesis by amine catalyzed sulfurization of isocyanides with elemental sulfur

Isothiocyanates (ITCs) are typically prepared using amines and highly toxic reagents such as thiophosgene, its derivatives, or CS2. In this work, an investigation of a multicomponent reaction (MCR) using isocyanides, elemental sulfur and amines revealed that isocyanides can be converted to isothiocyanates using sulfur and catalytic amounts of amine bases, especially DBU (down to 2 mol%). This new catalytic reaction was optimized in terms of sustainability, especially considering benign solvents such as Cyrene™ or γ-butyrolactone (GBL) under moderate heating (40 °C). Purification by column chromatography was further optimized to generate less waste by maintaining high purity of the product. Thus, E-factors as low as 0.989 were achieved and the versatility of this straightforward procedure was shown by converting 20 different isocyanides under catalytic conditions, while obtaining moderate to high yields (34-95%).

Design and synthesis of hydrazinecarbothioamide sulfones as potential antihyperglycemic agents

New hydrazinecarbothioamides with a phenylsulfonyl group were synthesized and their structures were identified by different spectroscopic data (¹ H NMR, ¹³ C NMR, two-dimensional NMR, mass spectrometry, elemental analysis, and single-crystal X-ray analysis). The mechanism describing the formation of the products was also discussed. The antidiabetic activity of the isolated products was investigated histochemically. The synthesized sulfonylalkylthiosemicarbazide exhibited antihyperglycemic activity in streptozotocin-induced diabetic mice. Compounds 5a and 5c significantly lowered the blood glucose level to 103.3 ± 1.8 and 102 ± 3.9 mg/dl, respectively. Also, they caused a significant decrease in malondialdehyde levels and normalized the glutathione levels in streptozotocin-induced diabetic mice, compared with the diabetic group. The results suggest that the synthesized hydrazinocarbothioamides may effectively inhibit the development of oxidative stress in diabetes.

Copper-Promoted One-Pot Approach: Synthesis of Benzimidazoles

A facile, one-pot, and proficient method was developed for the production of various 2-arylaminobenzimidazoles. This methodology is based for the first time on a copper catalyst promoted domino C-N cross-coupling reaction for the generation of 2-arylaminobenzimidazoles. Mechanistic investigations revealed that the synthetic pathway involves a copper-based desulphurization/nucleophilic substitution and a subsequent domino intra and intermolecular C-N cross-coupling reactions. Some of the issues typically encountered during the synthesis of 2-arylaminobezimidazoles, including the use of expensive catalytic systems and the low reactivity of bromo precursors, were addressed using this newly developed copper-catalyzed method. The reaction procedure is simple, generally with excellent substrate tolerance, and provides good to high yields of the desired products.

Magnetic chitosan-copper nanocomposite: A plant assembled catalyst for the synthesis of amino- and N-sulfonyl tetrazoles in eco-friendly media

A greener, cost efficient and simple method is described to prepare copper nanoparticles (NPs) immobilized on the magnetic chitosan (one of the more versatile polysaccharides) using Euphorbia falcata leaf extract as reducing/stabilizing agent. The prepared catalyst (Cu NPs@Fe₃O₄-chitosan) was authenticated by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), Scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), thermogravimetry/derivative thermogravimetry (TG/DTG), Vibrating sample magnetometer (VSM), and elemental mapping. TEM analysis indicates that Cu NPs with average sizes in 5-10 nm range is formed on magnetic chitosan with the spherical morphology. The Cu NPs@Fe₃O₄-chitosan was employed as a new catalyst for the synthesis of different tetrazoles by the reaction of various secondary or tertiary cyanamides with sodium azide in water under reflux conditions. Easy separation by external magnetic field, mild reaction conditions, low cost and the reusability are some of the beneficial features of this catalyst.

Mercury-Free Automated Synthesis of Guanidinium Backbone Oligonucleotides

A new method for synthesizing deoxynucleic guanidine (DNG) oligonucleotides that uses iodine as a mild and inexpensive coupling reagent is reported. This method eliminates the need for the toxic mercury salts and pungent thiophenol historically used in methods aimed at preparing DNG oligonucleotides. This coupling strategy was readily translated to a standard MerMade 12 oligonucleotide synthesizer with coupling yields of 95% and has enabled the synthesis of a 20-mer DNG oligonucleotide, the longest DNG strand to date, in addition to mixed DNA-DNG sequences with 3-9 DNG inserts. Importantly, DNG oligonucleotides exhibit robust unaided cellular uptake as compared to unmodified oligonucleotides without apparent cellular toxicity. Taken together, these findings should greatly increase the accessibility of cationic backbone modifications and assist in the development of oligonucleotide-based drugs.

Construction of 5-Aminotetrazoles via in Situ Generation of Carbodiimidium Ions from Ketones Promoted by TMSN3/TfOH

A novel synthetic approach for the synthesis of 5-aminotetrazoles has been developed by employing simple ketones as substrates. This methodology involved the N₂-extrusion/aryl migration of azido complexes as the key step for the in situ generation of carbodiimidium ion, which could further react with hydrazoic acid and cyclize intramolecularly to provide 5-aminotetrazoles in good to excellent yields. In addition, the regioselectivity of the reaction was studied and rationalized by density functional theory calculations.

A silver(i)-catalyzed cascade bicyclization strategy for synthesis of 5H-benzo[d]tetrazolo[5,1-b][1,3]thiazines

A simple and efficient protocol for silver(i)-catalyzed tandem reaction of o-alkynylphenyl isothiocyanates with sodium azide has been developed, affording a series of 5H-benzo[d]tetrazolo[5,1-b][1,3]thiazines in moderate to good yields. In this transformation, a [3 + 2] cycloaddition reaction mechanism was involved and two new rings were formed in one pot.

Organophosphine-free copper-catalyzed isothiocyanation of amines with sodium bromodifluoroacetate and sulfur

A copper-catalyzed isothiocyanation of amines with sodium bromodifluoroacetate and sulfur in the absence of organophosphine has been established. This approach represents a simple and efficient one-pot synthesis of isothiocyanates, and features excellent functional group tolerance and the use of a cheap, safe and odorless sulfur source. Moreover, this process could directly provide isothiocyanate analogous bioactive molecules, thiocarbonyl-containing pesticides and facile construction of benzoxazole and benzimidazole frames.

Hetero-bimetallic cooperative catalysis for the synthesis of heteroarenes

Review covering the synthesis of 5- and 6-membered as well as condensed heteroarenes, focussing on the combinations in cooperative catalytic systems in strategies used to achieve selectivity and also highlights the mode of action for the cooperative catalysis leading to the synthesis of commercially and biologically relevant heteroarenes.

Iodine-catalyzed guanylation of amines withN,N′-di-Boc-thiourea

Iodine-catalyzed guanylation of amines withN,N′-di-Boc-thiourea is especially useful for both electronically and sterically deactivated primary anilines.

Copper-catalyzed synthesis of 2-aminophenyl benzothiazoles: a novel approach

Substituted 2-aminophenyl benzothiazoles have been constructed from thiourea via copper-catalyzed desulfurization/nucleophilic substitution followed by domino intra- and intermolecular C–N cross-coupling reactions under moderate reaction conditions.

The synthesis of arylcyanamides: a copper-catalyzed consecutive desulfurization and C–N cross-coupling strategy

A one pot highly efficient and simple protocol for the construction of aromatic cyanamides from thioureaviadesulphurization/C–N cross coupling using a cheap, readily available and air stable copper source as a catalyst has been described.

Facile Synthesis of 1-(4-Bromophenyl)-1H-Tetrazol-5-Amine and Related Amide Derivatives

An efficient one-pot synthesis of 1-(4-bromophenyl)-1 H-tetrazol-5-amine was performed using 4-bromoaniline as the starting material. A novel and widely applicable amidation procedure was then employed, whereby 1-(4-bromophenyl)-1 H-tetrazol-5-amine was acylated with different acyl chlorides in the presence of lithium bis(trimethylsilyl)amide as catalyst, for the high-yield synthesis of [1-(4-bromophenyl)-1 H-tetrazol-5-yl]amide derivatives.

Molecular iodine induced/1,3-dipolar cycloaddition/oxidative aromatization sequence: an efficient strategy to construct 2-substituted benzo[f]isoindole-1,3-dicarboxylates

A useful method for a molecular iodine induced 1,3-dipolar cycloaddition/oxidative aromatization sequence to construct 2-substituted-benzo[f]isoindole-1,3-dicarboxylates is reported.