A three-component approach to isoxazolines and isoxazoles under metal-free conditions

Lewis acid-promoted direct synthesis of isoxazole derivatives

Isoxazole derivatives were synthesized via a one-pot method utilizing 2-methylquinoline derivatives as template substrates, sodium nitrite as a nitrogen-oxygen source, and solely using aluminum trichloride as the additive. This approach circumvents the need for costly or highly toxic transition metals and presents a novel pathway for the synthesis of isoxazole derivatives.

Three-Component Tandem Amidosulfenylation of Alkenes for the Synthesis of β-Succinimide Sulfides

An environmentally benign multicomponent strategy for the amidosulfenylation of alkenes for the synthesis of β-succinimide sulfides is disclosed. In this process, common disulfides smoothly act as a sulfur-based source, and N-iodosuccinimide (NIS) is used not only as a free radical initiator but also as an N-nucleophile. A broad range of functional groups are tolerated in this reaction system.

Synthesis of fused 3-trifluoromethyl-1,2,4-triazoles via base-promoted [3 + 2] cycloaddition of nitrile imines and 1H-benzo[d]imidazole-2-thiols

Here we report a strategy for the facile assembly of fused 3-trifluoromethyl-1,2,4-triazoles, which are difficult to synthesize using traditional strategies, in 50-96% yields through a triethylamine-promoted intermolecular [3 + 2] cycloaddition pathway. This protocol features high efficiency, good functional group tolerance, mild conditions, and easy operation. Furthermore, a gram-scale reaction and product derivatizations were carried out smoothly to illustrate the practicability of this method.

One-Pot Synthesis of Isoxazole-Fused Tricyclic Quinazoline Alkaloid Derivatives via Intramolecular Cycloaddition of Propargyl-Substituted Methyl Azaarenes under Metal-Free Conditions

A practical method was developed for the convenient synthesis of isoxazole-fused tricyclic quinazoline alkaloids. This procedure accesses diverse isoxazole-fused tricyclic quinazoline alkaloids and their derivatives via intramolecular cycloaddition of methyl azaarenes with tert-butyl nitrite (TBN). In this method, TBN acts as the radical initiator and the source of N-O. Moreover, this protocol forms new C-N, C-C, and C-O bonds via sequence nitration and annulation in a one-pot process with broad substrate scope and functionalization of natural products.

Direct Transformation of Nitrogen-Containing Methylheteroarenes to Heteroaryl Nitrile by Sodium Nitrite

The cyanation reaction of methylheteroarenes with acetyl chloride and sodium nitrite via the radical process in high yields is reported. According to the control experiments, the reaction mechanism underwent radical progress. It is very useful in the pharmacy industry due to its metal-free and easy treatment conditions.

Solvent-free synthesis of 3,5-isoxazoles via 1,3-dipolar cycloaddition of terminal alkynes and hydroxyimidoyl chlorides over Cu/Al2O3 surface under ball-milling conditions

Scalable, solvent-free synthesis of 3,5-isoxazoles under ball-milling conditions has been developed. The proposed methodology allows the synthesis of 3,5-isoxazoles in moderate to excellent yields from terminal alkynes and hydroxyimidoyl chlorides, using a recyclable Cu/Al₂O₃ nanocomposite catalyst. Furthermore, the proposed conditions are reproducible to a 1.0-gram scale without further milling time variations.

A practical and scalable mechanochemical 1,3-dipolar cycloaddition between hydroxyimidoyl chlorides and terminal alkynes catalyzed by Cu/Al₂O₃ allows a quick access to 3,5-isoxazole derivatives.

Generation of azaarene nitrile oxides from methyl azaarenes and t-BuONO enabling the synthesis of furoxans and 1,2,4-oxadiazoles

A high-efficiency strategy for the synthesis of furoxans and 1,2,4-oxadiazoles has been developed, using tert-butyl nitrite (TBN) as the nitrogen source. Azaarene nitrile oxides were generated in situ via methyl azaarenes functionalization.

[2 + 2 + 1] Heteroannulation of Alkenes with Enynyl Benziodoxolones and Silver Nitrite Involving C≡C bond Oxidative Cleavage: Entry to 3-Aryl-Δ2-isoxazolines

A copper-catalyzed [2 + 2 + 1] heteroannulation of alkenes with enynyl benziodoxolones and AgNO₂ involving oxidative cleavage of the C≡C bond promoted by cooperative Zn(OTf)₂, KOAc, and 4 Å MS for producing 3-aryl Δ²-isoxazolines is reported. Mechanistic studies indicate that AgNO₂ serves as the N/O two-atom unit source, enabling the formation of three bonds through NO₂ addition across the C≡C bond, NO-transfer, C≡C bond cleavage, and annulation cascades.

Recent advances in metal catalyzed or mediated cyclization/functionalization of alkynes to construct isoxazoles

This review summarized the recent developments in metal catalyzed or mediated cyclization/functionalization of alkynes to construct isoxazoles.

Recent synthetic efforts in the preparation of 2-(3,4)-alkenyl (aryl) quinoline molecules towards anti-kinetoplastid agents

Leishmaniasis, Chagas disease and African sleeping sickness have been considered some of the most important tropical protozoan afflictions. As the number of drugs currently available to treat these human illnesses is severely limited and the majority has poor safety profiles and complicated administration schedules, actually there is an urgent need to develop new effective, safe and cost-effective drugs. Because quinoline alkaloids with antiprotozoal activity (quinine, chimanine, cryptolepine or huperzine groups) were historically and are still essential models for drug research to combat these parasitic infections, synthetic or semi-synthetic quinoline-based molecules are important for anti-kinetoplastid drug design approaches and synthetic methods of their preparation become a key task that is the central subject of this review. Its goal is to highlight the advances in the conventional and current syntheses of new 2-(3,4)-alkenyl (aryl) quinoline derivatives, which kill the most important kinetoplastid protozoa, – Leishmania and Trypanosoma and could be useful models for antileishmanial and antitrypanosomal research. An attempt has been made to present and discuss the more recent contributions in this field over the period 2015–2019, paying special attention to molecular design, synthetic efforts to new green reaction conditions for classical methods such as Skraup synthesis, Friedländer synthesis, Conrad–Limpach, Doebner–Miller, as well as contemporary methods like Gould–Jacobs, Meth–Cohn and Povarov reactions. This review includes brief general information on these neglected tropical diseases, their current chemotherapies, and primary natural models (quinoline alkaloids), suitable for development of anti-kinetoplastid quinoline-based agents. The main part of the review comprises critical discussion on the synthesis and chemistry of new quinolines diversely substituted by alkyl (alkenyl, aryl) fragments on the pyridine part of the quinoline skeleton, which could be considered interesting analogues of chimanine alkaloids. The methods described in this review were developed with the aim of overcoming the drawbacks of the traditional protocols using revolutionary precursors and strategies.

Leishmaniasis, Chagas disease and African sleeping sickness have been considered some of the most important tropical protozoan afflictions.

Enantioselective dearomative [3+2] annulation of 5-amino-isoxazoles with quinone monoimines

Enantioselective dearomative [3+2] annulation of 5-amino-isoxazoles with quinone monoimines provided various (bridged) isoxazolines fused dihydrobenzofurans with moderate to good yields in moderate to good enantioselectivities.