Pyridinium Ylide-Mediated Diastereoselective Synthesis of Spirocyclopropanyl-pyrazolones via Cascade Michael/Substitution Reaction

We have devised a highly diastereoselective formal [2 + 1] annulation reaction of arylidene/alkylidine-pyrazolones with in situ-generated supported as well as standard pyridinium ylides to construct spirocyclopropanyl-pyrazolones. The cascade approach exhibits a wide range of functional group tolerance, gram-scale capability, and substrate versatility. A diverse range of spirocyclic cyclopropanes was synthesized extensively with both mediators, and the supported pyridine was reused in subsequent cycles. Density functional theory calculations confirmed the formation of spirocyclopropane as the lower energy pathway.

Organocatalyzed Heterocyclic Transformations In Green Media: A Review

Background:

Since the discovery of metal-free catalysts or organocatalysts about twenty years ago, a number of small molecules with different structures have been used to accelerate organic transformations. With the development of environmental awareness, to obtain highly efficient scaffolds, scientists have directed their studies towards synthetic methodologies that minimize or preferably eliminate the formation of waste, avoid toxic solvents and reagents and use renewable starting materials as far as possible.

Methods:

In this connection, the organocatalytic reactions providing efficiency and selectivity for most of the transformations have become an endless topic in organic chemistry since several advantages from both practical and environmental standpoints. Organocatalysts contributing to the transformation of reactants into products with the least possible waste production, have been serving the concept of green chemistry.

Results and Conclusion:

Organocatalysts have been classified based on their binding capacity to the substrate with covalent or noncovalent interactions involving hydrogen bonding and electrostatic interaction. Diverse types of small organic compounds including proline and its derivatives, phase-transfer catalysts, (thio)urease, phosphoric acids, sulfones, N-oxides, guanidines, cinchona derivatives, aminoindanol, and amino acids have been utilized as hydrogen bonding organocatalysts in different chemical transformations.

On the Exceptionally High Loading of L-Proline on Multi-Wall Carbon Nanotubes

L-proline is directly loaded on the multi-wall carbon nanotubes (MWCNTs) with exceptionally high loading content of 67 wt.%. The obtained L-proline/MWCNTs catalyst is on par with the catalytic activity of free L-proline, even after 7 rounds of recycling and reusing. The excellent activity of L-proline/MWCNTs in typical Aldol reaction, Mannich reaction, Michael reaction, α-oxyamination reaction, and Knoevenagel condensation shows a broad applicability of the composite catalyst in different reactions and solvent systems. We believe that the unusual loading mode may open a window for designing heterogenized organo-catalysts.

Polymer-Bound Triphenylphosphine and 4,4'-Dinitroazobenzene as a Coupling Reagents for Chromatography-Free Esterification Reaction

AIM AND OBJECTIVE

Sustainable production of fine chemicals both in industries and pharmaceuticals heavily depends on the application of solid-phase synthesis route coupled with microwave technologies due to their environmentally benign nature. In this report, a microwave-assisted esterification reaction using polymer-bound triphenylphosphine and 4,4'-dinitroazobenzene reagent system was investigated.

MATERIALS AND METHODS

The solvents were obtained from Merck India. Polymer-bound triphenylphosphine (~3 mmol triphenylphosphine moiety/g) was acquired from Sigma-Aldrich. The progress of the reaction was observed by thin-layer chromatography. All the reactions were performed in Milestones StartSYNTH microwave. The NMR spectra were recorded on Bruker Avance III 300, 400, and 500 MHz FT NMR Spectrometers. Using azo compound and polymer-bound triphenyl phosphine as a coupling reagent, esterification of different carboxylic acids with alcohols was performed under microwave irradiation.

RESULTS

Esterification of benzoic acid with 1-propanol under microwave irradiation gave a high yield of 92% propyl benzoate in 60 minutes only. Isolation of the ester products was relatively simple as both the byproducts polymer-bound triphenylphosphine oxide and hydrazine could be removed by simple filtration. The rates of reactions were found to be directly proportional to the pKa of the benzoic acids.

CONCLUSION

4,4'-Dinitroazobenzene was introduced as a novel coupling reagent, in conjugation with polymer-bound triphenylphosphine, for esterification reactions under microwave irradiation. The low moisture sensitivity of the reaction system, easy separation of the byproducts, and column chromatographyfree isolation of esters help our methods with application significance, particularly from the 'Sustainable Chemistry' perspective.

Minimizing solvent waste in catalytic reactions in highly recyclable hydrocarbon solvents

This paper describes chemistry using organocatalysts in hydrocarbon solvents that minimizes solvent waste by using inexpensive, non-volatile, relatively inflammable, and easily recyclable poly(α-olefin)s (PAOs) as hydrocarbon solvents. These studies show that when substrates have limited solubility in PAO solvents, this issue can be addressed by adding a small amount of a cosolvent. Kinetic studies were also carried out and show that reactions carried out in PAOs are kinetically comparable to reactions in conventional non-recyclable hydrocarbon solvents. A range of strategies that separate and isolate products from reactions in PAOs using a polyisobutylene (PIB)-supported DMAP catalyst have been studied using four different catalytic reactions. In the most general procedure, the PAO phase containing a PIB-bound catalyst is separated from products by low energy liquid/liquid gravity separation. This can be accomplished using a minimal amount of a polar solvent. In another example, the product's low solubility leads to it precipitating during the reaction. In this case, a simple filtration recycles the PAO and a PIB-bound DMAP catalyst. We have demonstrated that the PAO phase containing a PIB bound DMAP catalyst can be recycled for at least 10 cycles without loss of activity. Our studies further showed that leaching of the PAO phase into polar solvents was orders of magnitude less than conventional hydrocarbon solvents such as heptane. The result is that the overall solvent waste generation is lower than for the same reaction carried out in conventional solvents.

Wealth from waste: M. acuminata peel waste-derived magnetic nanoparticles as a solid catalyst for the Henry reaction

Biosynthesis of nanoparticles by exploiting different plant materials has become a matter of great interest in recent years and is considered as a green technology as it does not involve any harmful and toxic chemicals in the synthetic procedure. In this paper, we report a novel one-pot M. acuminata peel ash extract mediated bio-synthesis of basic iron oxide nanoparticles (MAPAE@Fe₃O₄). The nanoparticles were fully characterized by different analytical techniques such as XRF, IR, XRD, XPS, SEM, TEM, VSM and TGA. The synthesized nanoparticles exhibited high basicity due to the presence of metal oxides, primarily basic K₂O in the outer layer of Fe₃O₄ surfaces, and showed good catalytic activity for the synthesis of β-nitroalcohol via the Henry reaction at room temperature under solvent-free conditions. The catalyst was separated from the reaction medium by simply applying an external bar magnet making the process economical and less labor intensive. Furthermore, the catalyst can be reused up to the 4^th cycle without much loss of its activity.

Waste-to-useful: a biowaste-derived heterogeneous catalyst for a green and sustainable Henry reaction

Owing to the depletion of resources coupled with increasing waste generation, the conversion of waste biomass to value-added materials has gained interest.