Pinacol Rearrangement and Direct Nucleophilic Substitution of Allylic Alcohols Promoted by Graphene Oxide and Graphene Oxide CO2H

Metal-Free Construction of Multisubstituted Indolizines via Intramolecular Amination of Allylic Alcohols

An intramolecular amination of allylic alcohols is developed as an efficient and general access to biologically important multisubstituted indolizines and their variants. Two metal-free synthetic platforms including using aqueous hydrochloric acid solution as the solvent and p-toluenesulfonic acid as the catalyst have been established, enabling the divergent synthesis of these valuable compounds in high yields.

Carbocatalysis: a metal free green avenue towards carbon–carbon/heteroatom bond construction

Indeed, all the heterocycles comprises of either “C–C, C–N, C–S or C–O” bonds in their skeleton and construction of these bonds has laid the foundation stone of organic chemistry. The present researchers are continually attempting to develop new strategies for synthesizing miscellaneous structurally divergent molecular entities and these bond forming reactions are the fundamental tools. As a consequence, a colossal upheaval is witnessed in development of benign and sustainable synthetic routes for green bond-forming reactions envisaging carbon–carbon/heteroatom. This chapter is aimed towards highlighting the recent developments perceived in “C–C, C–N, C–S or C–O” bondconstruction especially emphasising greener perspectives i.e. carbocatalysis.

Boron-catalyzed dehydrative allylation of 1,3-diketones and β-ketone esters with 1,3-diarylallyl alcohols in water

A metal-free catalytic allylation with atom economy and green environment friendly was developed. Allylic alcohols could be directly dehydrated in water by B(C6F5)3, without using any base additives. The reaction can afford the corresponding monoallylated product in moderate to high yield and has been performed on a gram-scale, and a quaternary carbon center can be constructed for the active methine compounds of 1,3-diketones or β-ketone esters in this process. The product can be further converted, such as the synthesis of tetra-substituted pyrazole compounds, or 1,4-dienes and functionalized dihydropyrans.

Graphene Oxide as a Mediator in Organic Synthesis: a Mechanistic Focus

Graphene oxide (GO) is experiencing growing interest by synthetic organic chemists as a promoter of chemical transformations. The synergistic role of the multiple functionalities featuring the nanostructured carbon materials and their π-domains enables the interplay of specific activation modes towards organic compounds that can explore unprecedented chemical modifications. A detailed comprehension of the mechanistic details that govern the transformations guided by GO is a not fully solved task in the field. In this direction, more sophisticated and diversified techniques are employed, providing insights towards intriguing activation modes exerted by the π-matrix and the oxygenated/sulfonate groups decorating the functionalized nano-carbon material. The present Minireview accounts for a critical survey of the most recent developments in the area of GO-mediated organic transformations with a specific focus on mechanist aspects.

Dehydration in water: frustrated Lewis pairs directly catalyzed allylization of electron-rich arenes and allyl alcohols

A frustrated Lewis pair (FLP)-catalyzed allylation of allyl alcohols with electron-rich arenes has been developed. Interestingly, in this reaction, the electron-rich arenes and allyl alcohols are dehydrated in water. What's more, water was the sole byproduct of the reaction. In this protocol, various allyl alcohols can be converted into allyl cations and attacked by the electron-rich arenes to form aryl cation intermediates. Finally, the aryl cation intermediates are deprotonated to give the 1,3-diarylpropenes. In this protocol, indole allyl alcohols can undergo a bimolecular ring closure reaction, and structurally diverse tetrahydroindolo[3,2-b]carbazoles could be smoothly obtained. The reaction is not sensitive to oxygen and has been performed on a gram-scale.

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

β-Hydroxyalkylphosphine sulfides undergo [1,3]- or [1,4]-sulfur atom phosphorus-to-carbon migration in the presence of Lewis or Brønsted acids. The direction of sulfur atom migration depends on the type of acid used for the reaction. In the presence of a Brønsted acid, mainly [1,3]-rearrangement is observed, whereas a Lewis acid catalyzes the [1,4]-sulfur migration. To gain insight into the mechanism of these transformations, the stereochemistry of these rearrangements have been tested, along with the conduction of some control experiments and DFT calculations.

Heterogeneous graphene oxide as recyclable catalyst for azomethine ylide mediated 1,3 dipolar cycloaddition reaction in aqueous medium

Graphene oxide (GO) catalyzed regio and diastereoselective synthesis of spiro-indenoquinoxaline pyrrolizidines and spiro-oxindoles pyrrolizidines is described with good substrate scope and yield using azomethine ylide under aq. EtOH condition at RT.

Sulfonated reduced graphene oxide catalyzed cyclization of hydrazides and carbon dioxide to 1,3,4-oxadiazoles under sonication

Acid catalysts facilitate many chemical reactions. Sulfonated reduced grapheneoxide (rGOPhSO₃H) has shown to be an encouraging solid acid catalyst because of its efficiency, cost-effectiveness and safety of use. In this study, we prepared the rGOPhSO₃H nano acid catalyst, with the introduction of aromatic sulfonic acid radicals onto GO by fractional removal of oxygenated functions. It was thoroughly characterized by FT-IR, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, energy dispersive spectroscopy (EDS) and solid state ¹³C MAS NMR (SSNMR). Here we report the conversion of CO₂ (1.0 atm pressure, at = 50 °C, the source of C₁ carbon feed stock) with hydrazides and a catalytic amount rGOPhSO₃H, which through a cyclization reaction results in a new strategy for the synthesis of 5-substituted-3H-[1,3,4]-oxadiazol-2-ones (SOxdOs) under ultrasonic irradiation. Hence this concept of cyclization opens up for new insights

Recent advances in organic reactions catalyzed by graphene oxide and sulfonated graphene as heterogeneous nanocatalysts: a review

Over the past decade, the application of carbocatalyst systems has been preferred over that of homogeneous catalytic systems because of their advantages such as physical and thermal stability of the catalysts in successive reaction runs and reusability.