Derivatization of an especially electron-rich diborane

Starting with electron-rich ditriflato-diborane B2(hpp)2(OTf)2 (hpp = 1,3,4,6,7,8 hexahydro-2H-pyrimido[1,2-α]pyrimidinate), novel symmetric and unsymmetric diboranes B2(hpp)2X2 and B2(hpp)2XY with X,Y = Br, NCS, N3 or OTf are synthesized by substitution reactions...

Theoretical Prediction and Explanation of Reaction Site Selectivity in the Addition of a Phenoxy Group to Perfluoropyrimidine, Perfluoropyridazine, and Perfluoropyrazine

Perfluoroaromatics, such as perfluoropyridine and perfluorobenzene, are privileged synthetic scaffolds in organofluorine methodology, undergoing a series of regioselective substitution reactions with a variety of nucleophiles. This unique chemical behavior allows for the synthesis of many perfluoroaromatic derived molecules with unique and diverse architectures. Recently, it has been demonstrated that perfluoropyridine and perfluorobenzene can be utilized as precursors for a variety of materials, ranging from high performance polyaryl ethers to promising drug scaffolds. In this work, using density functional theory, we investigate the possibility of perfluoropyrimidine, perfluoropyridazine, and perfluoropyrazine participating in similar substitution reactions. We have found that the first nucleophilic addition of a phenoxide group substitution on perfluoropyrimidine and on perfluoropyridazine would happen at a site para to one of the nitrogen atoms. While previous literature points to mesomeric effects as the primary cause of this phenomenon, our work demonstrates that this effect is enhanced by the fact that the transition states for these reactions result in bond angles that allow the phenoxide to π-complex with the electron-deficient diazine ring. The second substitution on perfluoropyrimidine and on perfluoropyridazine is most likely to happen at the site para to the other nitrogen. The second substitution on perfluoropyrazine is most likely to happen at the site para to the first substitution. The activation energies for these reactions are in line with those reported for perfluoropyridine and suggest that these platforms may also be worth investigation in the lab as possible monomers for high performance polymers.

A convenient approach for the electrochemical bromination and iodination of pyrazoles

Electrochemical bromination and iodination of some pyrazoles were investigated under constant-current (CC) electrolysis in an undivided electrochemical cell. Anodic oxidation of KX salt produces X2 in-situ which can be consumed as an expedient electrophile in pyrazoles aromatic electrophilic substitution reactions or may participate in an X–N coupling reaction with electrochemically catalyzed pyrazolesox to form the halogenated pyrazoles. All reactions proceeded without the need to use any hazardous reagents or catalysts. The reaction conditions are mild and environmentally compatible.

Asymmetric Rhodium-Catalyzed Allylic Substitution Reactions with Nitrile-Stabilized Carbanions

This Account summarizes our recent work on rhodium-catalyzed allylic alkylation reactions with nitrile-stabilized carbanions. Despite the challenges associated with employing nitrile stabilized nucleophiles in transition-metal-catalyzed reactions, we recently developed both enantiospecific and enantioselective allylic alkylation reactions. Notably, these novel reactions permit the expedient and selective access to an array of acyclic ternary and quaternary stereogenic centers that are present in important biologically active molecules. 1 Introduction 2 Enantiospecific Reactions of Nitrile-Stabilized Anions 3 Enantioselective Reactions of Nitrile-Stabilized Anions 4 Conclusion

Antiviral Activities of Halogenated Emodin Derivatives against Human Coronavirus NL63

The current COVID-19 outbreak has highlighted the need for the development of new vaccines and drugs to combat Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2). Recently, various drugs have been proposed as potentially effective against COVID-19, such as remdesivir, infliximab and imatinib. Natural plants have been used as an alternative source of drugs for thousands of years, and some of them are effective for the treatment of various viral diseases. Emodin (1,3,8-trihydroxy-6-methylanthracene-9,10-dione) is a biologically active anthraquinone with antiviral activity that is found in various plants. We studied the selectivity of electrophilic aromatic substitution reactions on an emodin core (halogenation, nitration and sulfonation), which resulted in a library of emodin derivatives. The main aim of this work was to carry out an initial evaluation of the potential to improve the activity of emodin against human coronavirus NL63 (HCoV-NL63) and also to generate a set of initial SAR guidelines. We have prepared emodin derivatives which displayed significant anti-HCoV-NL63 activity. We observed that halogenation of emodin can improve its antiviral activity. The most active compound in this study was the iodinated emodin analogue E_3I, whose anti-HCoV-NL63 activity was comparable to that of remdesivir. Evaluation of the emodin analogues also revealed some unwanted toxicity to Vero cells. Since new synthetic routes are now available that allow modification of the emodin structure, it is reasonable to expect that analogues with significantly improved anti-HCoV-NL63 activity and lowered toxicity may thus be generated.

Regioselective Amination or Alkoxylation of Halogenated Amino-, Thio- or Alkoxypyridines via Pyridyne Intermediates

The treatment of 3-halopyridines (Cl, Br) bearing an R-substituent in position 2 (R = OEt, NEt2, N-piperidyl, or SEt) or in position 5 (R = OMe, OEt, SEt, NMe2, NEt2, or aryl) with KHMDS and an amine at 25 °C for 12 hours in THF provided regioselectively 3- and 4-aminated pyridines in 56–90% yields. The reaction of 3-bromo-2-diethylaminopyridine with various alcohols in the presence of t-BuOK/18-crown-6 in THF at 80 °C for 20–60 hours gave various 4-alkoxy-2-diethylaminopyridines in 61–81% yields. These substitution reactions were proposed to proceed via pyridyne intermediates.

Synthesis of Triazine based Dendrimers: A Mini-Review

: Synthesizing s-triazine dendrimers are interesting as they can be synthesized easily, contain diversity in composition, and have a basic potential for molecular recognition. Triazine trichloride is the molecule of choice for synthesizing a novel class of dendrimers as it possesses certain remarkable characteristics like the potential to expand the chemical functionality by nucleophilic aromatic substitution reactions at various temperatures to give the desired dendrimer.