Alkynoates as Versatile and Powerful Chemical Tools for the Rapid Assembly of Diverse Heterocycles under Transition-Metal Catalysis: Recent Developments and Challenges

Heterocycles, heteroaromatics and spirocyclic entities are ubiquitous components of a wide plethora of synthetic drugs, biologically active natural products, marketed pharmaceuticals and agrochemical targets. Recognizing their high proportion in drugs and rich pharmacological potential, these invaluable structural motifs have garnered significant interest, thus enabling the development of efficient catalytic methodologies providing access to architecturally complex and diverse molecules with high atom-economy and low cost. These chemical processes not only allow the formation of diverse heterocycles but also utilize a range of flexible and easily accessible building units in a single operation to discover diversity-oriented synthetic approaches. Alkynoates are significantly important, diverse and powerful building blocks in organic chemistry due to their unique and inherent properties such as the electronic bias on carbon-carbon triple bonds posed by electron-withdrawing groups or the metallic coordination site provided by carbonyl groups. The present review highlights the comprehensive picture of the utility of alkynoates (2007-2019) for the synthesis of various heterocycles (> 50 types) using transition-metal catalysts (Ru, Rh, Pd, Ir, Ag, Au, Pt, Cu, Mn, Fe) in various forms. The valuable function of versatile alkynoates (bearing multifunctional groups) as simple and useful starting materials is explored, thus cyclizing with an array of coupling partners to deliver a broad range of oxygen-, nitrogen-, sulfur-containing heterocycles alongside fused-, and spiro-heterocyclic compounds. In addition, these examples will also focus the scope and reaction limitations, as well as mechanistic investigations into the synthesis of these heterocycles. The biological significance will also be discussed, citing relevant examples of drug molecules highlighting each class of heterocycles. This review summarizes the recent developments in the synthetic methods for the synthesis of various heterocycles using alkynoates as readily available starting materials under transition-metal catalysis.

Microwave Assisted Surfactant-Thermal Synthesis of Metal-Organic Framework Materials

This research explores the application of surfactants as green solvents for the rapid microwave synthesis of metal-organic framework (MOF) materials. Lead, copper, and iron metal-organic framework materials were synthesized using surfactant-thermal microwave synthesis. The MOF materials were characterized by powder X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. With the exception of the iron MOF, which was expected to be amorphous, the MOF materials are crystalline, though generally exhibiting smaller crystals than those achieved with traditional solvothermal synthesis. This green synthetic method reduced synthesis time and reduced the use of traditional organic solvents as the reaction media.

Cascade Rh(ii) and Yb(iii) catalyzed synthesis of substituted naphthofurans via transannulation of N-sulfonyl-1,2,3-triazoles with β-naphthols

Synthesis of substituted naphthofurans has been achieved via an efficient cascade Rh(ii)/Yb(iii) catalyzed transannulation of N-sulfonyl-1,2,3-triazoles with β-naphthols.

Solubility of Some Mineral Salts in Polyethylene Glycol and Related Surfactants

The ambient solubility of the mineral salts NaCl, KCl, CsCl, KBr, K2SO4 and CuSO4 is reported as a function of composition of mixed binary solvents consisting of water with polyethylene glycol (PEG 200), ethoxylated C9–11 alcohols (C10E6) and ethoxylated, or propoxylated C10–12 alcohols (C11E6P1). Solubility gradually decreases with decreasing water content and follows the order PEG 200 > C10E6 > C11E6P1. Solubility of CsCl and KBr was found to be surprisingly high in neat PEG 200, on the order of 1 mol kg−1, and in neat C10E6, on the order of 0.1 mol · kg−1. The observed solubility trends are explained by the theory of hard and soft acids and bases under the consideration of the polarity of the surfactants.

A simple green protocol for the synthesis of ethyl 3-amino-1-aryl-1H-benzo[f] chromene-2-carboxylates in aqueous media

An eco-friendly and efficient straightforward method has been developed for the synthesis of ethyl 3-amino-1-aryl-1 H-benzo[ f]chromene-2-carboxylate derivatives via 1,4-diazabicyclo[2.2.2]octane (DABCO)-catalysed cyclisation of β-naphthol and 3-aryl-2-cyanoacrylates using water as a green solvent. All products precipitated from the reaction mixture and were isolated by simple filtration. No further work-up nor purification was necessary. The structure of ethyl 3-amino-1-aryl-1 H-benzo[ f]chromene-2-carboxylate was further confirmed by X-ray single crystal analysis.

Green Suzuki Coupling Reaction for Synthesis of Abiraterone Acetate and its Analogues

An eco-friendly efficient method was developed for the synthesis of abiraterone acetate and analogues in water-PEG-400 (6:1; v/v) at 75°C from various arylboronic acids and 17-(trifluoromethanesulfonyl)oxy-3β-acetoxylandrosta-5,16-diene obtained from the 3-acetate of dehydroepiandrosterone.

Three-component reaction between substituted 2-(2-nitrovinyl)-phenols, acetylenedicarboxylate and amines: diversity-oriented synthesis of novel pyrrolo[3,4-c]coumarins

The diversity-oriented synthesis of pyrrolo[3,4-c]coumarins via FeCl₃-promoted three component reaction between substituted 2-(2-nitrovinyl)phenols, acetylenedicarboxylate and amines has been developed.

One-pot synthesis of 2,4,6-triarylpyridines from β-nitrostyrenes, substituted salicylic aldehydes and ammonium acetate

The diversity-oriented synthesis of 2,4,6-trisubstituted pyridines via K₂CO₃-promoted multicomponent reactions of the β-nitrostyrenes, available substituted salicylic aldehydes and ammonium acetate have been developed.

Expedient synthesis of nitrovinyl substituted bicyclo[2.2.2]octenone scaffolds

A simple and rapid oxidative acetalization and Diels–Alder protocol of nitrovinyl substituted guaiacols has been developed to synthesize nitrovinyl-bearing bicyclo[2.2.2]octenone derivatives.