A Route to Triazole-Fused Sultams via Metal-Free Base-Mediated Cyclization of Sulfonamide-Tethered 5-Iodotriazoles

Access to Bicyclo[3.1.0]hexane and Cyclopenta[c]pyrazole Scaffolds via Solvent-Directed Divergent Reactivity of 5-Iodotriazoles

Divergent access to bicyclo[3.1.0]hexane and cyclopenta[c]pyrazole scaffolds bearing azole and azine units has been developed. The approach involves intramolecular cyclization of 5-iodo-1,2,3-triazoles acting as stable diazoimine precursors with concomitant noncatalytic (3 + 2)-cycloaddition. The choice of solvent allows control of the outcome of the cascade transformation. The developed procedure is simple and cost-efficient and allowed important heterocycles to be obtained in one-pot with various functional groups.

Novel convenient 2-step synthesis of pyrido[1,2-a]indoles from pyrylium salts and o-bromoanilines

A novel convenient 2-step synthesis of substituted pyrido[1,2-a]indoles is developed starting from easily available pyrylium tetrafluoroborates and ortho-bromoanilines. A conversion of the pyrylium tetrafluoroborates to pyridinium ones followed by their palladium catalyzed intramolecular cyclization allows the formation of 24 examples of N-fused heterocycles. A one-pot two-stage cyclization procedure was developed. The utility of the methodology was demonstrated with the synthesis of new pyrido[1,2-a]indoles bearing different alkyl, aryl, chlorine, fluorine and methoxy substituents.

Facile preparation of polycyclic halogen-substituted 1,2,3-triazoles by using intramolecular Huisgen cycloaddition

When 1-(ω-azidoalkyl)-2-(2,2-dihalovinyl)arenes were heated in DMF, the intramolecular Huisgen cycloaddition of an azido group with a 1,1-dihalovinyl group afforded 5-halo-1,2,3-triazole-fused tricyclic benzo compounds. Based on the remaining bromo groups, carbon elongation by the Mizoroki-Heck or Suzuki-Miyaura coupling reactions, followed by an intramolecular Friedel-Crafts reaction, afforded polycyclic compounds with fused triazole rings. Thereafter, the bromo groups were converted into 2-nitrophenyl groups via the Suzuki-Miyaura coupling reaction, which was followed by the Cadogan reaction; a fluorescent pentacyclic compound was obtained.

A Copper-Catalyzed Interrupted Domino Reaction for the Synthesis of Fused Triazolyl Benzothiadiazine-1-oxides

Copper(I)-catalyzed domino reactions of 2-azido sulfoximines with 1-iodoalkynes yield fused triazolyl-containing benzothiadiazine-1-oxides. The protocol features the synthesis of two fused heterocyclic rings in one step with good to excellent yields and a broad functional group tolerance. Detailed mechanistic investigations indicate that a copper π-complex initiates a cycloaddition and oxidative C-N coupling reaction sequence. The results suggest an interrupted domino process involving an iodinated triazole as a key intermediate.

Domino assembly of dithiocarbamates via Cu-catalyzed denitrogenative thiolation of iodotriazole-based diazo precursors

An efficient domino approach to assemble benzoxazoles and anthranilamides bearing dithiocarbamate moieties has been developed. The proposed route represents a Cu-catalyzed three-component reaction between readily available 5-iodo-1,2,3-triazoles, amines, and CS₂. The cascade transformation is based on a denitrogenative coupling of in situ formed dithiocarbamic acids with diazo intermediates, generated via annulation-triggered triazole ring-opening. This method is applicable to nucleophilic secondary amines and features good functional group compatibility.

Annulation-Triggered Denitrogenative Transformations of 2-(5-Iodo-1,2,3-triazolyl)benzoic Acids

The ability of [1,2,3]triazolobenzoxazinones to act as a source of "hidden" diazo group was discovered. These diazo precursors can be easily prepared by the intramolecular cyclization of 2-(5-iodo-1,2,3-triazolyl)benzoic acids. The Cu-catalyzed capture of the hidden diazo group allows for further functionalization through the denitrogenative pathway. The transformations proceed via the formation of either diazoimine or diazoamide intermediates. Novel routes to various anthranilamides as well as thiolated benzoxazinones were developed using the one-pot cyclization/diazo capture procedure.

Facile Access to Triazole-Fused 3,1-Benzoxazines Enabled by Metal-Free Base-Promoted Intramolecular C–O Coupling

A convenient approach to assemble 1,2,3-triazole-fused 4H-3,1-benzoxazines has been developed. Diverse alcohol-tethered 5-iodotriazoles, readily accessible by a modified protocol of Cu-catalyzed (3+2)-cycloaddition, were utilized as precursors of the target fused heterocycles. The intramolecular C–O coupling proceeded efficiently under base-mediated transition-metal-free conditions, furnishing cyclization products in yields up to 96%. Suppression of the competing reductive cleavage of the C–I bond was achieved by the use of Na2CO3 in acetonitrile at 100 °C. This practical and cost-effective procedure features a broad substrate scope and valuable functional group tolerance.

A recent overview on the synthesis of 1,4,5-trisubstituted 1,2,3-triazoles

Diverse strategies for the efficient and attractive synthesis of a wide variety of relevant 1,4,5-trisubstituted 1,2,3-triazole molecules are reported. The synthesis of this category of diverse fully functionalized 1,2,3-triazoles has become a necessary and unique research subject in modern synthetic organic key transformations in academia, pharmacy, and industry. The current review aims to cover a wide literature survey of numerous synthetic strategies. Recent reports (2017–2021) in the field of 1,4,5-trisubstituted 1,2,3-triazoles are emphasized in this current review.

Domino Construction of Benzoxazole-Derived Sulfonamides via Metal-Free Denitrogenation of 5-Iodo-1,2,3-triazoles in the Presence of SO2 and Amines

A straightforward domino approach to assemble benzoxazole-derived sulfonamides has been developed. The method is based on annulation-induced in situ generation of diazo compounds from readily available 2-(5-iodo-1,2,3-triazolyl)phenols, followed by metal-free denitrogenative transformation upon the action of 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) (DABSO) and amines. The protocol is operationally simple and features a broad substrate scope, furnishing a library of target compounds in generally good yields.

Assembly of Thiosubstituted Benzoxazoles via Copper-Catalyzed Coupling of Thiols with 5-Iodotriazoles Serving as Diazo Surrogates

An efficient cascade approach to thiosubstituted benzoxazoles has been developed. The transformation starts with in situ generation of a diazo compound via annulation-triggered electrocyclic opening of the 1,2,3-triazole ring. The subsequent Cu-catalyzed trapping of diazo intermediates by various thiols affords the desired heterocycles in generally good yields of up to 91%. The protocol features very good functional group tolerance and is applicable to substrates with different electronic properties.