C−H Bond Functionalization in the Synthesis of Fused 1,2,3-Triazoles

Entropy-Induced Selectivity Switch in Gold Catalysis: Fast Access to Indolo[1,2-a]quinolines

New N-heterocyclic compounds for organic functional materials and their efficient syntheses are highly demanded. A surprising entropy-induced selectivity switch in the gold-catalyzed intramolecular hydroarylation of 2-ethynyl N-aryl indoles was found and its exploitation led to straightforward syntheses of indolo[1,2-a]quinolines. Experimental and computational mechanistic investigations gave insight into this uncommon selectivity phenomenon and into the special reactivity of the indolo[1,2-a]quinolines. The high functional group tolerance of this methodology enabled access to a diverse scope with high yields. In addition, bidirectional approaches, post-functionalization reactions, and π-extension of the core structure were feasible. An in-depth study of the photophysical properties explored the structure-effect relationship for different derivatives and revealed a high potential of these compounds for future applications as functional materials.

Stitching Triazoles to Arenes via a Transition Metal-Free Aryne Diels-Alder/1,3-Prototropic Shift/Dehydrobromination Cascade

The 1,2,3-triazole-fused polyaromatic frameworks are traditionally obtained through transition metal-catalyzed C-H/C-X arylation of the preinstalled triazoles at a very high temperature. Herein, a transition metal-free direct synthesis via an aryne Diels-Alder/1,3-prototropic shift/dehydrobromination cascade is reported. This method gives access to triazole-fused aromatics as well as the corresponding dihydrocarbocycles under mild reaction conditions.

Fused benzo[1,3]thiazine-1,2,3-triazole hybrids: Microwave-assisted one-pot synthesis, in vitro antibacterial, antibiofilm, and in silico ADME studies

In this paper, we report an efficient one-pot three-component reaction sequences comprising Cu(I)-catalyzed 1,3-dipolar cycloaddition (CuAAC) followed by Cu-catalyzed arylation of resulting 1,2,3-triazole in the presence of ionic liquid [Emim]BF₄ under microwave conditions involving. The newly synthesized derivatives were screened for in vitro antibacterial inhibition potency against both gram +ve and gram -ve strains. Among the tested compounds, 4f exhibited significant inhibition activity with MIC value 3.12 µg/mL against B. subtilis and S. epidermidis which is two-fold higher than the standard ciprofloxacin (6.25 µg/mL) and also displayed equipotent activity to that of the positive control against S. aureus with MIC value 6.25 µg/mL. Conjugates of the series viz. 3f and 4b against S. aureus, and 4e against E. coli have also displayed promising results with MIC values 6.25 µg/mL which is comparable to the ciprofloxacin. Also we report the anti-biofilm profiles for the potent compounds and it was observed from the results that the active derivatives 4b and 4f were not only potent antibacterial agents but also efficient inhibitors of B. subtilis and S. aureus biofilm growth. Furthermore, in silico-ADME and pharmacokinetic profiles demonstrated the druggability of the hybrids.

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

An efficient direct approach to triazole-fused sultams has been developed. The key step of the proposed strategy is base-mediated cyclization of sulfonamide-tethered 5-iodo-1,2,3-triazoles which are readily available via an improved protocol for Cu-catalyzed 1,3-dipolar cycloaddition. The annulation of the sultam fragment to the triazole ring proceeds smoothly under transition-metal-free conditions in the presence of Cs₂CO₃ in dioxane at 100 °C and affords fused heterocycles in high yields up to 99%. The favorability of an S_NAr-like mechanism for the cyclization was supported by DFT calculations. The applicability of the developed procedure to modification of natural compounds was demonstrated by preparation of a deoxycholic acid derivative.

Catalyst-free facile synthesis of polycyclic indole/pyrrole substituted-1,2,3-triazoles

A general and catalyst-free access to the fused polycyclic N-heterocycles via an intramolecular azide-alkene cascade reaction under mild reaction conditions has been developed. The reaction is applicable to both indole and pyrrole substrates, and a variety of substituents are tolerated. The entire sequence can be carried out in a one-pot operation. This methodology provides a sustainable and efficient access to a variety of novel polycyclic indole/pyrrole substituted-1,2,3-triazoles.

1-Iodobuta-1,3-diynes in Copper-Catalyzed Azide-Alkyne Cycloaddition: A One-Step Route to 4-Ethynyl-5-iodo-1,2,3-triazoles

Cu-catalyzed 1,3-dipolar cycloaddition of iododiacetylenes with organic azides using iodotris(triphenylphosphine)copper(I) as a catalyst was found to be an efficient one-step synthetic route to 5-iodo-4-ethynyltriazoles. The reaction is tolerant to various functional groups in both butadiyne and azide moieties. The synthetic application of 5-iodo-4-ethynyl triazoles obtained was also evaluated: the Sonogashira coupling with alkynes resulted in unsymmetrically substituted triazole-fused enediyne systems, while the Suzuki reaction yielded the corresponding 5-aryl-4-ethynyl triazoles.

Metal-free sulfonyl radical-initiated cascade cyclization to access sulfonated indolo[1,2-a]quinolines

A metal-free cascade reaction was developed for the synthesis of indolo[1,2-a]quinoline derivatives from arylsulfonyl hydrazides and 1-(2-(arylethynyl)phenyl)indoles in the presence of TBAI/TBHP.

Regioselective synthesis of multisubstituted 1,2,3-triazoles: moving beyond the copper-catalyzed azide-alkyne cycloaddition

Copper(i)-catalyzed azide-alkyne cycloaddition (CuAAC) is an essential "click chemistry" reaction that is widely used in chemical biology, medicinal chemistry and materials science. The CuAAC reaction of terminal alkynes provides a mild and efficient synthesis of 1,4-disubstituted 1,2,3-triazoles. However, the click reaction of internal alkynes with azides, giving trisubstituted triazoles, is very challenging. This feature article highlights the recent progress addressing this fundamental problem. Particular emphasis is on the current and emerging strategies to introduce functional groups to the C-5 position of triazoles in a regioselective manner.

Chemoselective and stereospecific iodination of alkynes using sulfonium iodate(i) salt

The sulfonium iodate(i) electrophilc reagent efficiently promoted the stereodivergent iodination of alkynes. The chemoselective iodination was effectively realized by switching the solvent system to access the 1-iodoalkyne and (E)-vicinal-diiodoalkenes.

A facile synthesis of diverse 5-arylated triazoles via a Cu-catalyzed oxidative interrupted click reaction with arylboronic acids in air

A Cu-catalyzed synthesis of 5-arylsubstituted 1,2,3-triazoles via an oxidative interrupted click reaction with arylboronic acids in air at room temperature is disclosed.

Using gene expression database to uncover biology functions of 1,4-disubstituted 1,2,3-triazole analogues synthesized via a copper (I)-catalyzed reaction

We have synthesized bioactive 1,4-disubstituted 1,2,3-triazole analogues containing 2H-1,4-benzoxazin-3-(4H)-one derivatives via 1,3-dipolar cycloaddition in the presence of CuI. All the reactions proceeded smoothly and afforded its desired products in excellent yields. Among these analogues, 3y exhibited a better cytotoxic effect on human hepatocellular carcinoma (HCC) Hep 3B cells and displayed less cytotoxicity on normal human umbilical vein endothelial cells, compared with Sorafenib, a targeted therapy for advanced HCC. 3y also induced stronger apoptosis and autophagy. Addition of curcumin enhanced 3y-induced cytotoxicity by further induction of autophagy. Using gene expression signatures of 3y to query Connectivity Map, a glycogen synthase kinase-3 inhibitor (AR-A014418) was predicted to display similar molecular action of 3y. Experiments further demonstrate that AR-A014418 acted like 3y, and vice versa. Overall, our data suggest the chemotherapeutic potential of 3y on HCC.

One-pot synthesis of fused benzoxazino[1,2,3]triazolyl[4,5-c]quinolinone derivatives and their anticancer activity

Cu/Pd catalyzed one pot synthesis of fused benzoxazino[1,2,3]triazolyl[4,5-c]quinolinone hybrids and their cytotoxic activity against human cancer cell lines MCF-7, HeLa and A-549 is described.

Sequential decarboxylative azide-alkyne cycloaddition and dehydrogenative coupling reactions: one-pot synthesis of polycyclic fused triazoles

Herein, we describe a one-pot protocol for the synthesis of a novel series of polycyclic triazole derivatives. Transition metal-catalyzed decarboxylative CuAAC and dehydrogenative cross coupling reactions are combined in a single flask and achieved good yields of the respective triazoles (up to 97% yield). This methodology is more convenient to produce the complex polycyclic molecules in a simple way.

One-pot three-component synthesis of 1,4,5-trisubstituted 5-iodo-1,2,3-triazoles from 1-copper(i) alkyne, azide and molecular iodine

The desired 5-iodo-1,2,3-triazoles were synthesized conveniently without using the pre-made 1-iodoalkynes as substrates.

Copper(I)-catalyzed cycloaddition of bismuth(III) acetylides with organic azides: synthesis of stable triazole anion equivalents

Fully loaded: Readily accessible and shelf-stable 1-bismuth(III) acetylides react rapidly and regiospecifically with organic azides in the presence of a copper(I) catalyst. The reaction tolerates many functional groups and gives excellent yields of the previously unreported 5-bismuth triazolides. This uniquely reactive intermediate is functionalized under mild reaction conditions to give fully substituted 1,2,3-triazoles.

Tandem reaction of 1-copper(I) alkynes for the synthesis of 1,4,5-trisubstituted 5-chloro-1,2,3-triazoles

A novel tandem reaction of 1-copper(I) alkynes with azides (cycloaddition) and then NCS (electrophilic substitution) was developed as an efficient method for the synthesis of 1,4,5-trisubstituted 5-chloro-1,2,3-triazoles. The method offers a rare example that a tandem reaction of an organometallic substrate does not involve in the reactivity of the metal-carbon bond in the first step.