Alumina-promoted synthesis of N-aryl-1,2,4-triazoles from substituted hydrazines and imides

From (-)-sclareol to Norlabdane Heterocyclic Hybrid Compounds

This review relates to chemistry of the well-known biologically active natural labdane diterpenoid (-)-sclareol easily available from Clary sage (Salvia sclarea L.). It is mainly used in industry, especially for synthesis of fragrance compounds and natural analogs. The paper covers achievements on the synthesis, structure determination and biological activity of molecular hybrid compounds bearing hydrazide and thiosemicarbazone fragments or diazine, 1,2,4-triazole, carbazole, 1,3-thiazole, 1,3,4-oxadiazole, 1,3,4-thiadiazole units prepared based on it.

Metal- and Oxidant-Free Green Three-Component Desulfurization and Deamination Condensation Approach to Fully Substituted 1H-1,2,4-Triazol-3-amines and Their Photophysical Properties

A metal- and oxidant-free three-component desulfurization and deamination condensation of amidines, isothiocyanates, and hydrazines for the synthesis of structurally diverse fully substituted 1H-1,2,4-triazol-3-amines is described. The reaction proceeds without the requirement of any external catalysts, metals, ligands, or oxidants. This [2 + 1 + 2] cyclization strategy involves C-N and C-S bond cleavage and the formation of new C-N bonds in one pot. This transformation provides a series of full substituted 1H-1,2,4-triazol-3-amines with advantages of a broad substrates scope, mild reaction conditions, environmental friendliness, and easy gram-scale applications. The fluorescence and aggregation-induced emission (AIE) properties of selected products were further tested. These synthesized 1H-1,2,4-triazol-3-amines may be worth investigating for further applications in the fields of organic chemistry, medicinal chemistry, and optical materials.

From Heterocycles to Carbacycles: Synthesis of Carbocyclic Nucleoside Analogues from Enals and Hydroxylamines

Substituted and stereochemically dense carbacycles can be prepared by sequential dipolar cycloaddition and reductive cleavage from enals and hydroxylamines. The reaction sequence proceeds with high efficiency for a wide variety of enals and hydroxylamines. The reaction is regio- and diastereoselective for the initial formation of a bridged bisisoxazolidine intermediate, which then undergoes quantitative double N-O cleavage to produce carbacycles as single diastereomers.

Synthesis of Chromenoisoxazolidines from Substituted Salicylic Nitrones via Visible-Light Photocatalysis

This effort reports the first redox-neutral visible-light photocatalytic intramolecular dipolar cycloaddition for the diastereoselective synthesis of chromenoisoxazolidines. The authors have found that alkenylphenyl nitrones with a diverse substitution pattern on the aromatic ring and the alkenyl substituent undergo visible-light-promoted cycloadditions in the presence of catalytic amounts of Ru(bpy)₃Cl₂ in high yields and selectivities. Evidence indicates that the proposed redox-neutral pathway is the predominant photoredox mechanism for this transformation.

Visible light-induced cyclization reactions for the synthesis of 1,2,4-triazolines and 1,2,4-triazoles

1,2,4-Triazolines and 1,2,4-triazoles can be synthesized under visible light in one step without additional operations, which can be also scaled up to a gram-level.

Recent Developments on Ultrasound-Assisted Synthesis of Bioactive N-Heterocycles at Ambient Temperature

N-Heterocycles represent privileged structural subunits well distributed in naturally occurring compounds with immense biological activities. The last decade has seen a tremendous practice to carry out reactions at ambient temperature avoiding harsh reaction conditions. By applying ultrasonic radiation in organic synthesis we can make synthetic protocols more sustainable and can carry out reactions at room temperature avoiding the traditional thermal harsh reaction conditions. Therefore the synthesis of biologically relevant N-heterocycles at room temperature under the influence of ultrasonic irradiation is one of the advancing areas in the 21st century among organic chemists. The present review summarises the latest developments on ultrasound-assisted synthesis of biologically relevant N-heterocycles at ambient temperature.