Fabrication of Heterogeneous-based Lacunary Polyoxometalates as Efficient Catalysts for the Multicomponent and Clean Synthesis of Pyrazolopyranopyrimidines

Novel pyromellitic diamide–diacid bridged mesoporous organosilica nanospheres with controllable morphologies and acidic centers were designed and prepared through a convenient method by altering the addition sequence of precursors, solvent, and aging time. 

Pyromellitic diamide–diacid bridged mesoporous organosilica nanospheres with controllable morphologies: a novel PMO for the facile and expeditious synthesis of imidazole derivatives

In this work, novel pyromellitic diamide–diacid bridged mesoporous organosilica (PMAMOS) nanospheres with controllable morphologies and Bronsted acid catalytic centers were designed and prepared through a convenient method by altering the addition sequence of precursors, solvent, and aging time. The obtained PMAMOSs demonstrate high surface areas and uniform pore sizes. FESEM, HRTEM, BET, EDX, XRD, FTIR and TGA analyses were performed to characterize and examine the effective factors for the preparation of PMAMOS nanospheres. Due to the appropriate physicochemical properties including Bronsted acid centers, suitable surface area and thermal stability of the PMAMOS nanosphere material, it was explored in the three-component reaction of benzyl or benzoin, ammonium acetate, and different aldehyde derivatives as a case study of multicomponent reactions. Corresponding imidazole derivatives were obtained in EtOH under reflux conditions in high to quantitative yields and short reaction times. It was also shown that the heterogeneous solid acid can be reused at least five times with negligible loss of its catalytic activity, indicating the appropriate stability and high activity of the newly introduced mesoporous organosilica.

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The simultaneous binding/dissociation of multiple bonds in a one-pot manner by multicomponent reactions provide an important approach for developing novel and sustainable pathway in the drug discovery process. Herein we develop an electrocatalytic three-component reaction to construct multifunctional and valuable isothiourea compounds, which uses thiols, isocyanides and amines as substrates. Compared with the previous work, the organic electrosynthesis technique can avoid the requirement of heavy metal catalysts and stoichiometric oxidants. In addition, using thiol as a substrate to participate in the three-component reaction broadens the source of sulfur, which can also construct more abundant isothiourea derivatives. 

Electrochemically mediated three-component synthesis of isothioureas using thiols as sulfur source

Multicomponent reactions (MCRs) have been gaining significance and attention over the past decade because of their ability to furnish complex products by using readily available and simple starting materials while simultaneously eliminating the need to separate and purify any intermediates. More so, most of these products have been found to exhibit diverse biological activities. Another paradigm shift which has occurred contemporarily is the switch to heterogeneous catalysis, which results in additional benefits such as the reduction of waste and an increase in the safety of the process. More importantly, it allows the user to recover and reuse the catalyst for multiple runs. In summary, both methodologies adhere to the principles of green chemistry, a philosophy which needs to become overarchingly enshrined. The plethora of reactions and catalysts which have been developed gives hope that chemists are slowly changing their ideology. As a result, this review attempts to discuss multicomponent reactions catalysed by operationally heterogeneous catalysts in the past 10 years. In this review, a further distinction is made between the MCRs which lead to the formation of heterocycles and those which do not.

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Recent Advances in Multicomponent Reactions Catalysed under Operationally Heterogeneous Conditions

Multi-component reactions (MCRs) are considered to be an important methodological arsenal in synthetic and medicinal chemistry. These reactions have been strategically employed in various synthetic transformations where classical methods usually involve many steps with tedious procedures. The MCR approach provides high yields, atom-/step economy, reduced reaction time, is eco-friendly, and acts as an amenable tool for the generation of a library of new chemical entities (NCEs), especially in the drug discovery process. Extensive research has led to copious developments in the field of MCRs. The developments have emerged with different synthetic approaches, including C–H activation, coupling, and cycloaddition, and eventually, such an amalgamation has enabled access to a broad spectrum of organic frameworks. The present review summarizes recent advancements in MCRs and their mechanistic insights from the last triennium (2017–2020).

Recent advances in multi-component reactions and their mechanistic insights: a triennium review

Microwave-assisted (MWA) multicomponent reactions (MCRs) have successfully emerged as one of the useful tools in the synthesis of biologically relevant heterocycles. These reactions are strategically employed for the generation of a variety of heterocycles along with multiple point diversifications. Over the last few decades classical MCRs such as Ugi, Biginelli, etc. have witnessed enhanced yield and efficiency with microwave assistance. The highlights of MWA-MCRs are high yields, reduced reaction time, selectivity, atom economy and simpler purification techniques, such an approach can accelerate the drug discovery process. The present review focuses on the recent advances in MWA-MCRs and their mechanistic insights over the past decade and shed light on its advantage over the conventional approach.

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Shivani Gulati

Papers

Recent advances in multi-component reactions and their mechanistic insights: a triennium review

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects.