Current Organic Chemistry - Volume 24, Issue 19, 2020

Decarboxylative addition reactions are well known as an effective approach to C–C bonds formation due to the availability of starting reagents, ease of handling, and low environmental impact. This approach clearly demonstrated its potential for the synthesis of the variety of acyclic and heterocyclic compounds, including optically active ones. The significant amount of articles devoted to this topic published in recent years proves the importance of this approach in modern organic synthesis. In this review, the recent achievements in decarboxylative addition to C=C, C=N, and C=O bonds have been summarized and discussed over the last 6 years.

In the last decade, the use of heterogeneous catalysts based on Metal Nanoparticles (MNPs) has attracted increasing attention due to their prominence as nanocatalysts in several key chemical transformations. Notably, it is well identified that supporting Metal Nanoparticles (MNPs) with suitable solid surfaces can protect the MNPs from leaching, deactivation, and also increasing its ease of separation and possible reusability. Graphene oxide (GO) as a conductive surface could have non-covalent bonding interactions like hydrogen bonding, electrostatic and π –π* stacking interactions with substrate leading to activation of the substrate. Remarkably, it is recognized that bimetallic nanoparticles supported on graphene oxide often show novel properties that are not present on either of the parent metal or surfaces. In this review, we tried to reveal the potential advantages of bimetallic and trimetallic nanoparticles supported on graphene oxide in organic transformations, including the reduction of nitroarenes, Suzuki-Miyaura and Sonogashira coupling reactions.

C-N coupling reactions were found to be attractive among researchers owing to the importance of C-N bond formation in heterocyclic synthesis. Hence C-N bond formation via amination reaction with the assistance of microwave radiations gained significant attraction recently. Microwave-assisted reactions are greener, faster and generally efficient compared to the conventional thermal reactions offering better purity of the product with enhancement in the yield. It was surprisingly revealed that several new advancements in amination reactions were highly influenced by this greener technology. This first review on microwave-assisted amination reaction focuses on the novel amination strategies that emerged with the help of microwave methodology, and covers literature up to 2019.

Benzo[b]thiophenes are aromatic heterocyclic compounds containing benzene and thiophene rings. This class of heterocycles is present in a large number of natural and non-natural compounds. Benzo[b]thiophene derivatives have a broad range of applications in medicinal chemistry such as antimicrobial, anticancer, antioxidant, anti-HIV and antiinflammatory activities. The use of benzo[b]thiophene derivatives in other fields has also been reported. Various benzo[b]thiophenes compounds have been employed as organic photoelectric materials, while several benzo[b]thiophenes have been used as organic semiconductors. Benzo[b]thiophenes have also been used as building blocks or intermediates for the synthesis of pharmaceutically important molecules. Due to such a wide range of applicability, the synthesis of benzo[b]thiophene derivatives has attracted intensive research. Numerous mild and efficient approaches for the synthesis of benzo[b]thiophenes have been developed over the years. Different catalysts and substrates have been applied for benzo[b]thiophene synthesis. This review will focus on the studies in the construction of benzo[b]thiophene skeleton, which date back from 2012.

Several 6- and 7-alkoxy-2-oxo-2H-chromene-4-carbaldehydes were prepared from corresponding alkyl ethers of 6- and 7-hydroxy-4-methyl-2-oxo-2H-chromen-2-ones by oxidation using selenium dioxide. 6- and 7-Alkoxy-4-methyl-2H-chromenes were obtained with yields of 57-85%. Corresponding 4-carbaldehyde derivatives were prepared with yields of 41-67%. Thiosemicarbazones of these aldehydes with D-galactose moiety were synthesized by reaction of these aldehydes with N-(2,3,4,6-tetra-O-acetyl-β-Dgalactopyranosyl) thiosemicarbazide with yields of 62-74%. These thiosemicarbazones were screened for their antibacterial and antifungal activities in vitro against bacteria, such as Staphylococcus aureus, Escherichia coli, and fungi, such as Aspergillus niger, Candida albicans. Several compounds exhibited strong inhibitory activity with MIC values of 0.78- 1.56 μM, including 8a (against S. aureus, E. coli, and C. albicans), 8d (against E. coli and A. niger), 9a (against S. aureus), and 9c (against S. aureus and C. albicans).

A simple, efficient, and cheap strategy has been developed for N-arylation of indoles with hexafloro benzene (1) via incorporating sulfolane as an eco-friendly solvent. NMonopentafluoroarylindole (3) at ambient conditions and N, N-bistetrafluoroaryl indole (4) at elevated temperatures were conveniently obtained by simple nucleophilic substitution using NaOH as the base and sulfolane as a reaction medium to obtain in moderately good yields, respectively. Subsequently, 3-chloro, 3-bromo, and 3-iodomono-pentafluoroarylindoles and 3, 3’-dichloro, 3, 3’-dibromo and 3, 3’-diIodobistetrafluoroaryl indoles were prepared in good yields by using respective halogenating reagents and solvents. All the chemical transformations were confirmed by analytical tools such as 1HNMR, FR-IR and HRMS analysis.