Synthesis of 3H-1,2,4-Triazol-3-ones via NiCl2-Promoted Cascade Annulation of Hydrazonoyl Chlorides and Sodium Cyanate

AgNOx as Nitrogen Source for [1+1+3] Cycloaddition of Isocyanides with Isocyanates: Selective Synthesis of 1,2,4-Triazoles

A novel [1+1+3] annulation of AgNOx, isocyanides, and isocyanates for the selective synthesis of 1,2,4-triazoles is presented herein. In this transformation, AgNOx and isocyanates are used as nitrogen sources instead of the traditional hydrazine or diazonium reagents. This process also involves N-O/C-H/C═N bond cleavage and the construction of new N-N/C-N bonds with a good substrate scope and functional group tolerance.

Hydrazone Phosphaketene as a Synthetic Platform To Obtain Three Classes of 1,2,4-Diazaphosphol Derivatives by Switchable Chemoselectivity Strategies

We introduce switchable chemoselectivity strategies based on the hydrazone phosphaketene intermediate to synthesize three classes of 1,2,4-diazaphosphol derivatives. First, the five-membered heterocyclic P and O anion intermediates acted as nucleophilic agents in the selective construction of C-P and C-O bonds. Second, the phosphinidene served as a phosphorus synthon, allowing for the formation of C-P and C-N bonds. Finally, a stepwise mechanism, supported by DFT calculations, was invoked to explain the reaction selectivity.

Construction of 1,3,4-oxadiazolines bearing CF3-quaternary centers via amino-assisted [3 + 2] cycloadditions

An amino-assisted [3 + 2] cycloaddition strategy of nitrile imines with o-aminotrifluoroacetophenones has been explored, thus providing functionalized 1,3,4-oxadiazolines bearing CF3-quaternary centers in good to excellent yields in the presence of K2CO3 under mild conditions. The amino groups located at the ortho-position of trifluoroacetophenone might play a crucial role in the present cyclization. The MTT assay shows that the 1,3,4-oxadiazoline derivatives could be potential candidates for the treatment of head and neck cancers.

Radical selenylative cyclization of trifluoromethyl propargyl imines for the synthesis of trifluoromethyl- and seleno-azaspiro[4,5]-tetraenones and quinolines

A radical selenylative cyclization of trifluoromethyl propargyl imines with diselenides for the regiodivergent construction of diversely functionalized azaspiro[4,5]-tetraenones and quinolines has been developed, which enables dual incorporation of CF₃ and Se groups into heterocycles in a one-pot reaction. When using Oxone as a green oxidant, the reaction proceeds through oxidative dearomative ipso-annulation or intramolecular ortho-annulation exhibiting good regioselectivity. The synthetic utility of this method is demonstrated by a scale-up reaction and further modification of the obtained products.

Fluorinated and Non-Fluorinated 1,4-Diarylpyrazoles via MnO2-Mediated Mechanochemical Deacylative Oxidation of 5-Acylpyrazolines

A solvent-free two-step synthesis of polyfunctionalized pyrazoles under ball-milling mechanochemical conditions was developed. The protocol comprises (3 + 2)-cycloaddition of in situ generated nitrile imines and chalcones, followed by oxidation of the initially formed 5-acylpyrazolines with activated MnO2. The second step proceeds via an exclusive deacylative pathway, to give a series of 1,4-diarylpyrazoles functionalized with a fluorinated (CF3) or non-fluorinated (Ph, COOEt, Ac) substituent at C(3) of the heterocyclic ring. In contrast, MnO2-mediated oxidation of a model isomeric 4-acylpyrazoline proceeded with low chemoselectivity, leading to fully substituted pyrazole as a major product formed via dehydrogenative aromatization. The presented approach extends the scope of the known methods carried out in organic solvents and enables the preparation of polyfunctionalized pyrazoles, which are of general interest in medicine and material sciences.

Additive-Free Synthesis of 3H-1,2,4-Triazol-3-ones via a Formal [3+2] Cycloaddition Reaction of Hydrazonoyl Chlorides with KOCN

A direct and speedy approach for the synthesis of 1,5-disubstitued-3H-1,2,4-triazol-3-ones via a formal [3+2] cycloaddition reaction of hydrazonoyl chlorides with KOCN is described. The reaction proceeds in EtOH at room temperature with no need for any base and catalyst. KCl is the sole byproduct of this efficient synthetic procedure which can be isolated after reaction completion using water in which the products precipitated.

Method for Preparing N-Tosylhydrazonyl Chlorides

A facile and efficient method for preparing N-tosylhydrazonyl chlorides was developed. The reaction was general for a variety of substrates and displayed wonderful compatibility to diverse substituents. A range of N-tosylhydrazonyl chlorides was prepared for the first time.

Amide Bond Formation via the Rearrangement of Nitrile Imines Derived from N-2-Nitrophenyl Hydrazonyl Bromides

We report how the rearrangement of highly reactive nitrile imines derived from N-2-nitrophenyl hydrazonyl bromides can be harnessed for the facile construction of amide bonds. This amidation reaction was found to be widely applicable to the synthesis of primary, secondary, and tertiary amides and was used as the key step in the synthesis of the lipid-lowering agent bezafibrate. The orthogonality and functional group tolerance of this approach was exemplified by the N-acylation of unprotected amino acids.

TFBen (Benzene-1,3,5-triyl triformate): A Powerful and Versatile CO Surrogate

Carbonylative reactions by the using of CO surrogates constitute a facile avenue for the assembly of valuable carbonyl-containing compounds due to the colorless, toxic, flammable, and not easy-handing character of carbon monoxide gas. Recent advances in the carbonylative transformations with TFBen (benzene-1,3,5-triyl triformate) as a safe and convenient CO precursor are systematically summarized and discussed, which can be divided into three parts based on the patterns of the obtained products. This Review focuses on the discussion of the application of TFBen in carbonylative synthesis of various carbonyl-containing compounds.

Metal-free oxidative cyclization of trifluoroacetimidohydrazides with methylhetarenes: a facile access to 3-hetaryl-5-trifluoromethyl-1,2,4-triazoles

A metal-free oxidative cyclization of trifluoroacetimidohydrazides with methylhetarenes for the efficient synthesis of 3-hetaryl-5-trifluoromethyl-1,2,4-triazoles has been developed.