Lewis acid catalyst free synthesis of benzimidazoles and formamidines in 1,1,1,3,3,3-hexafluoro-2-propanol

13C-NMR Chemical Shifts in 1,3-Benzazoles as a Tautomeric Ratio Criterion

Benzimidazole is an important heterocyclic fragment, present in many biologically active compounds with a great variety of therapeutic purposes. Most of the benzimidazole activities are explained through the existence of 1,3-tautomeric equilibrium. As the binding affinity of each tautomer to a protein target depends on an established bioactive conformation, the effect of tautomers on the ligand protein binding mechanism is determinant. In this work, we searched and analyzed a series of reported ¹³C-NMR spectra of benzazoles and benzazolidine-2-thiones with the purpose of estimating their tautomeric equilibrium. Herein, several approaches to determine this problem are presented, which makes it a good initial introduction to the non-expert reader. This chemical shift difference and C4/C7 signals of benzimidazolidine-2-thione and 1-methyl-2-thiomethylbenzimidazole as references were used in this work to quantitatively calculate, in solution, the pyrrole–pyridine tautomeric ratio in equilibrium. The analysis will help researchers to correctly assign the chemical shifts of benzimidazoles and to calculate their intracyclic or exocyclic tautomeric ratio as well as mesomeric proportion in benzimidazoles.

Applications of alkyl orthoesters as valuable substrates in organic transformations, focusing on reaction media

In this review we focus on applications of alkyl orthoesters as valuable and efficient substrates to perform various classes of two-component and multi-component organic reactions. The article has classified them according to two aspects, which are: (i) a focus on the reaction medium (solvent-free conditions, aqueous media, and organic solvents); and (ii) an examination of product structures. Reaction accomplishment under solvent-free conditions is an eco-friendly process with the absence of volatile toxic solvents, which puts it in line with green chemistry goals. Water is an interesting choice in organic transformations due to its inexpensiveness and safety. The authors hope their assessment will help chemists to attain new approaches for utilizing alkyl orthoesters in various organic synthetic methods. The review covers the corresponding literature up to the beginning of 2020.

Solvent-mediated Highly Efficient Synthesis of [1,2,4]triazolo/benzimidazoloquinazolinone Derivatives

OBJECTIVE

An efficient and catalyst-free procedure for the synthesis of [1,2,4]triazolo/benzimidazolo quinazolinones has been developed in 2,2,2-trifluoroethanol or deep eutectic solvent(DESs) as a clean reaction media.

METHODS

All of the obtained products are known compounds and identified by IR, 1HNMR,13CNMR, and melting points.

RESULT

Various products were obtained in good to excellent yields under reaction conditions.

CONCLUSION

We have efficiently developed a practical and catalyst-free approach for the synthesis of [1,2,4]triazolo/benzimidazolo quinazolinones employing TFE as a clean and reusable media.

Metal–organic framework mediated expeditious synthesis of benzimidazole and benzothiazole derivatives through an oxidative cyclization pathway

Herein, we report facile synthesis of various benzimidazoles and benzothiazoles by using the NH₂-MIL-125(Ti) MOF as an efficient oxidant-free heterogeneous catalyst with good yield.

Gluco-1 H-imidazole: A New Class of Azole-Type β-Glucosidase Inhibitor

Gluco-azoles competitively inhibit glucosidases by transition-state mimicry and their ability to interact with catalytic acid residues in glucosidase active sites. We noted that no azole-type inhibitors described, to date, possess a protic nitrogen characteristic for 1 H-imidazoles. Here, we present gluco-1 H-imidazole, a gluco-azole bearing a 1 H-imidazole fused to a glucopyranose-configured cyclitol core, and three close analogues as new glucosidase inhibitors. All compounds inhibit human retaining β-glucosidase, GBA1, with the most potent ones inhibiting this enzyme (deficient in Gaucher disease) on a par with glucoimidazole. None inhibit glucosylceramide synthase, cytosolic β-glucosidase GBA2 or α-glucosidase GAA. Structural, physical and computational studies provide first insights into the binding mode of this conceptually new class of retaining β-glucosidase inhibitors.

Synthesis of N-Substituted 3-Amino-4-halopyridines: A Sequential Boc-Removal/Reductive Amination Mediated by Brønsted and Lewis Acids

N-Substituted 3-amino-4-halopyridines are valuable synthetic intermediates, as they readily provide access to imidazopyridines and similar heterocyclic systems. The direct synthesis of N-substituted 3-amino-4-halopyridines is problematic, as reductive aminations and base-promoted alkylations are difficult in these systems. A high yielding deprotection/alkylation protocol mediated by trifluoroacetic acid and trimethylsilyl trifluoromethanesulfonate is described, providing access to a wide scope of N-substituted 3-amino-4-halopyridines. This protocol furnishes many reaction products in high purity without chromatography. Similar reductive amination conditions were also established for deactivated anilines.

Nanoporous TiO2 containing an ionic liquid bridge as an efficient and reusable catalyst for the synthesis of N,N′-diarylformamidines, benzoxazoles, benzothiazoles and benzimidazoles

Nanoporous TiO₂ modified with an ionic liquid was used for efficient coupling of amines, 1,2-phenylene diamines, 2-aminophenol and 2-aminothiophenol with orthoesters.

B(C6F5)3-mediated transformations and hydrogenation of carbodiimides

The reactivity of a series of carbodiimides RNCNR (R=tBu (1 a), iPr (1 b), SiMe3 (1 c), and Dipp (2,6-di-iso-propylphenyl (1 d)) with B(C6 F5 )3 was investigated. After initial adduct formation, several distinct reaction pathways were identified. These pathways involve either isomerization of the carbodiimide to cyanamide derivatives or insertion of a carbodiimide into a BC bond of B(C6 F5 )3 to yield four-membered heterocycles. In the presence of dihydrogen, stepwise hydrogenation of the heteroallene moiety in the carbodiimides was achieved, which yielded the respective amidine-B(C6 F5 )3 adducts and amidinium borate salts upon reaction with one or two equivalents of H2 , respectively.

Overcoming product inhibition in catalysis of the intramolecular Schmidt reaction

A method for carrying out the intramolecular Schmidt reaction of alkyl azides and ketones using a substoichiometric amount of catalyst is reported. Following extensive screening, the use of the strong hydrogen-bond-donating solvent hexafluoro-2-propanol was found to be consistent with low catalyst loadings, which ranged from 2.5 mol % for favorable substrates to 25 mol % for more difficult cases. Reaction optimization, broad substrate scope, and preliminary mechanistic studies of this improved version of the reaction are described.

Evaluation of electrophilic heteroaromatic substitution: synthesis of heteroaromatic-fused pyrimidine derivatives via sequential three-component heterocyclization

A new sequential three-component heterocyclization was developed by reacting aromatic and heterocyclic substrates, including aminobenzenes, 1-aminonaphthalene, 2-aminopyrazines, 5-aminopyrazoles, 3-aminopyridine, 5-aminopyrimidine, 5-aminoquinoline, and 8-aminoquinoline, with formamide in the presence of PBr(3). The reaction gave the corresponding pyrazolo[3,4-d]pyrimidines in good yields (59-96%), except for aminobenzenes and 3-aminopyridine. A plausible reaction mechanism involving amidination, electrophilic substitution imination, and oxidative cyclization in three steps was proposed to account for the heterocyclization. The reactivity of the reaction was found proportional to the electrophilicity of the aromatic or heterocyclic substrate.