Hydrazide- and Diazole-Linked Covalent Organic Frameworks and Their Water Harvesting Properties

We report a retrosynthetic strategy and its implementation to making covalent organic frameworks (COFs) with irreversible hydrazide and diazole (oxadiazole and thiadiozole) linkages. This involved the synthesis of a series of 2D and 3D hydrazine-linked frameworks, followed by their oxidation and dehydrative cyclization. Each linkage synthesis and functional group transformation—hydrazine, hydrazide, oxadiazole, and thiadia-zole—was evidenced by 15N multi-CP-MAS NMR. In addition, the isothermal water uptake profiles of these frameworks were studied, leading to the discovery that one hydrazide-linked COF is suitable for water harvest-ing from air in arid conditions. These COFs displayed characteristic S-shaped water sorption profiles, a steep pore-filling step below 18% relative humidity at 25 °C, and a total uptake capacity of 0.45 g g–1 at P/Psat = 0.95. In addition, a total of ten 2D and 3D structures with various such linkages were studies for their affinity to water. We found that even small changes made on the molecular level can lead to major differences in the water isotherm profiles and therefore pointing to the utility of water sorption analysis as a complementary analytical tool to study linkage transformations.

Functional Group Transformation in Naphthoquinones: Strategies for the Synthesis of Mono- and Bis(Amino-1,4-naphthoquinones)

: 1,4-Naphthoquinones are a group of natural and synthetic substances that participate in various biochemical functions in most plants and animals, being involved in energy production, electron transport, blood coagulation and generation of reactive oxygen species (ROS), among others. The performance of such biochemical functions is directly related to the functional groups linked to the 1,4-naphthoquinone scaffold, and the introduction of nitrogen-containing groups into this nucleus may amplify its biological activity against numerous targets. Therefore, several methods have been developed in the last decades for preparing these compounds, especially from 1,4-naphthoquinone derivatives. Considering these concepts, in this review we aim to provide insights into the chemistry, chemical synthesis, semi-synthesis, pharmacological effects, and reactivity of low molecular weight mono- and bis(aminonaphthoquinones); we start by discussing the use of some of the most important 1,4-naphthoquinones as starting materials for the synthesis of amino-1,4-naphthoquinones (ANQs), go thought the modification of ANQ derivatives, and conclude by providing an outlook on this field.

Selective electrocatalytic hydroboration of aryl alkenes

A CH3CN-involved electrochemical mono- or di-functional borylation reaction with alkenes and HBpin as substrates was reported. Functional group transformation and gram-scale synthesis demonstrated the utility of this method and showed great potential application.

A CO2-Mediated Conjugate Cyanide Addition to Chalcones

Carbon dioxide is an intrinsically stable molecule; however, it can readily react with various nucleophilic reagents. In the presence of a cyanide source, CO2 was proven to be useful to promote addition reactions. Here we report the use of CO2 to facilitate 1,4-conjugate cyanide addition reaction to chalcones to generate organonitriles. Nitriles are key component in organic synthesis due to their utility in numerous functional group transformation, however, conjugation addition of cyanide has been a challenge in this substrate class due to side reactions. To mitigate this, we employed simple ammonium and metal cyanide sources as nucleophiles under carbon dioxide atmosphere where high selectivity toward the desired product was obtained. The presented reaction is not feasible under inert atmosphere, which highlights the important role of CO2, as a Lewis and Brøndsted acidic catalyst. Further derivatization of organonitriles compounds were performed to showcase the utility of the reaction, while an unprecedented dimerization reaction was identified and characterized, affording a cyclopentanone scaffold.

Natural Products Containing Olefinic Bond: Important Substrates for Semi-synthetic Modification Towards Value Addition

: Semi-synthesis, the way of preparing novel bioactive molecules via modification of compounds isolated from natural sources is very much useful nowadays in the drug discovery process. The modification is based on the reaction of functional group(s) present in a natural compound. Among the examples of functional group transformation, double bond modification is also common in the literature. Several reactions like hydrogenation, cyclopropanation, epoxidation, addition reaction (halogenations, hydroxylation), Michael addition, Heck reaction, cycloaddition, dipolar cycloaddition, etc. are employed for this purpose. In this review, we have tried to gather the reactions performed with several double bond containing classes of natural products like diterpenes, xanthones, sesquiterpene exomethylene lactones, diaryl heptanoids, steroidal lactones, triterpenoids, limonoids, and alkamides. Where available, the effects of transformations on the biological activities of the molecules are also mentioned.

A Concise Total Synthesis of (±)-Camptothecin

A total synthesis of racemic camptothecin, characterized by a concise construction of the ring systems and easy functional group transformation, is described. A domino reaction consisting of a Heck reaction and an aza-intramolecular Michael addition to form the C ring serves as the first key step in the synthesis. The D ring was constructed by a simple Wittig–Horner reaction followed by removal of the protective groups. Hydroxymethylation, demethylation, and lactone formation reactions were performed in one-pot to construct the E ring under hydrobromic acid conditions. This work provides an efficient scheme for further synthetic exploration of camptothecin and its analogues.