A thorough study on the reaction of DMAD with 1-arylaminoimidazole-2-thiones. Expeditious synthesis of imidazo[2,1-b][1,3]thiazoles through a novel arylamino rearrangement

Organocatalytic Activation of Alkynes Enabled Remote Control of Atroposelectivity via Vinylidene para-Quinone Methides

Axially chiral o-VQMs have been extensively investigated as key intermediates to approach miscellaneous chiral structures. By sharp contrast, their structural isomers p-VQMs have not been previously documented. The major reason, which results in the significant delay, may ascribe to the inherent challenges in the enantioselective activation of alkynes in a remote manner. Herein, we demonstrate that the remote activation mechanism of para-hydroxyl-substituted arylacetylenes enables significant stereochemical induction, resulting in axially chiral aryl-alkenes with excellent enantiopurities. A series of control experiments are performed to elucidate the insights of this asymmetric transformation and to verify the involvement of multimolecular CPAs in the reaction process. These findings are expected to unlock a new feature for VQM chemistry and inspire investigation into the organocatalytic remote control of stereoselectivity.

The vital use of isocyanide-based multicomponent reactions (MCR) in chemical synthesis

Multicomponent (MCRs) reactions are classified as one-pot reaction where more than two starting materials are employed to form a single product that contains the building blocks of the starting components. MCRs are considered a convenient approach in synthetic chemistry and have many advantages over the traditional one or two-component reaction, by reducing the number of sequential multiple steps required and often producing better yields. This chapter dissects the use of isocyanide-based MCRs and the elegant chemistry that they offer to build useful scaffolds in the chemical synthetic field. In addition MCRs are considered as one of the recognisable options for increasing “greenness” during the synthesis of pharmaceutical and industrial products.

Metal-free synthesis of quinoline-2,4-dicarboxylate derivatives using aryl amines and acetylenedicarboxylates through a pseudo three-component reaction

An efficient, useful and one-pot protocol for the synthesis of quinoline-2,4-dicarboxylate scaffolds is accomplished from aryl amines and dimethyl/diethyl acetylenedicarboxylates using 20 mol% molecular iodine as a catalyst in acetonitrile at 80 °C. In addition, the mechanistic explanation for the formation of the desired products is disclosed. The pivotal role of molecular iodine in the formation of the major products, diester quinoline derivatives, and the minor product, triesters, in two cases is described in the mechanism. The notable advantages of this method are non-involvement of a metal catalyst, avoiding of metal contamination in the final product as well as waste generation, use of a low cost and eco-friendly catalyst, ease of handling, high regioselectivity, shorter reaction time, the formation of one C-N and two C-C bonds and a broad substrate scope with good yields.

Site-selectivity control in hetero-Diels-Alder reactions of methylidene derivatives of lawsone through modification of the reactive carbonyl group: an experimental and theoretical study

A new perspective on the reactivity of hydroxyquinones was revealed as an acetal derivative of lawsone was synthesized, isolated, and used in tandem Knoevenagel/hetero-Diels-Alder reactions catalyzed by S-proline. The intermediate alkylidene-1,3-diones that were formed in situ reacted with electron rich alkenes to predominantly afford pyrano-1,2-naphthoquinone (β-lapachone) derivatives along with the isomeric pyrano-1,4-naphthoquinone (α-lapachone) derivatives in high to excellent total yields. Interestingly, the highly reactive arylidene-1,3-dione derivatives were found to be stable and isolable. DFT calculations suggest that these hetero-Diels-Alder reactions have a high polar character, taking place through a two-stage one-step mechanism. An analysis of the conceptual DFT indices allows explaining the remarkable site-selectivity observed.

Functionality of 4-amino-5-hydrazinyl-4H-1,2,4-triazole-3-thiol in synthesis of new fused triazolotriazines and triazolotriazepines of potential gram negative antibacterial activity

4-Amino-5-hydrazinyl-4 H-1,2,4-triazole-3-thiol reacted with dimethyl acetylene-dicarboxylate, ethyl propiolate, ( E)-1,2-dibenzoylethylene, 2-(1,3-dioxo-1 H-inden-2(3 H)-ylidene)malononitrile, 2,3-dichloro-1,4-naphthoquinone, 2,3,5,6-tetrachloro-1,4-benzoquinone and 3,4,5,6-tetrachloro-1,2-benzoquinone to give various novel heterocylic compounds. Seven chemically synthesised compounds were screened for their in vitro antimicrobial activity against different strains of microorganisms. Most of the tested compounds exhibited an excellent antibacterial activity against Gram negative bacteria including Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa compared to the activity of ciprofloxacin.