Flow-Integrated Preparation of Norbornadiene Precursors for Solar Thermal Energy Storage

Molecular solar thermal (MOST) energy storage systems are getting increased attention related to renewable energy storage applications. Particularly, 2,3-difunctionalized norbornadiene-quadricyclane (NBD-QC) switches bearing a nitrile (CN) group as one of the two substituents are investigated as promising MOST candidates thanks to their high energy storage densities and their red-shifted absorbance. Moreover, such NBD systems can be prepared in large quantities (a requirement for MOST-device applications) in flow through Diels-Alder reaction between cyclopentadiene and appropriately functionalized propynenitriles. However, these acetylene precursors are traditionally prepared in batch from their corresponding acetophenones using reactive chemicals potentially leading to health and physical hazards, especially when working on a several-grams scale. Here, we develop a multistep flow-chemistry route to enhance the production of these crucial precursors. Furthermore, we assess the atom economy (AE) and the E-factor showing improved green metrics compared to classical batch methods. Our results pave the way for a complete flow synthesis of NBDs with a positive impact on green chemistry aspects.

Novel benzenesulfonamide-bearing pyrazoles and 1,2,4-thiadiazoles as selective carbonic anhydrase inhibitors

Two series comprising 20 novel benzenesulfonamides bearing thioureido-linked pyrazole 8 and amino-1,2,4-thiadiazole 10 were synthesized and assayed as human carbonic anhydrase (hCA) inhibitors against isoforms I and II as well as the tumor-associated isoforms IX and XII. Molecular modeling studies of some potent derivatives (8a, 8c, 10a, and 10c) were also performed against isoforms hCA I, II, and XII. Both the promising series of compounds were synthesized by using commercially available mtethyl ketones and sulfanilamide as the starting materials. Interestingly, this paper also reports a novel methodology for the synthesis of amino-1,2,4-thiadiazoles 10 using 3-amino isoxazoles and 4-isothiocyanatobenzenesulfonamide as reactants. The activity profile of all the newly synthesized compounds reveals that amino-linked 1,2,4-thiadiazoles 10 were better inhibitors of the cytosolic isoform, hCA I, as compared to thioureido-linked pyrazoles 8. Further, hCA II was strongly inhibited by nearly all the newly synthesized sulfonamides, while all the compounds were less effective as hCA IX and XII inhibitors compared to the standard drug acetazolamide. However, in terms of selectivity, compound 8e was found to be the most selective inhibitor of hCA II, which is the isoform associated with glaucoma, edema, altitude sickness, and epilepsy.

Molecular solar thermal energy storage in photoswitch oligomers increases energy densities and storage times

Molecular photoswitches can be used for solar thermal energy storage by photoisomerization into high-energy, meta-stable isomers; we present a molecular design strategy leading to photoswitches with high energy densities and long storage times. High measured energy densities of up to 559 kJ kg⁻¹ (155 Wh kg⁻¹), long storage lifetimes up to 48.5 days, and high quantum yields of conversion of up to 94% per subunit are demonstrated in norbornadiene/quadricyclane (NBD/QC) photo-/thermoswitch couples incorporated into dimeric and trimeric structures. By changing the linker unit between the NBD units, we can at the same time fine-tune light-harvesting and energy densities of the dimers and trimers so that they exceed those of their monomeric analogs. These new oligomers thereby meet several of the criteria to be met for an optimum molecule to ultimately enter actual devices being able to undergo closed cycles of solar light-harvesting, energy storage, and heat release.

Molecular solar thermal systems are promising for storing solar energy but achieving high energy storage densities and absorption characteristics matching the solar spectrum is challenging. Here the authors present a design strategy for electronically coupled photoswitches which allow for high energy density storage for solar energy storage applications.

Regio- and Stereoselective Chlorocyanation of Alkynes

A variety of terminal and internal alkynes were converted regio- and stereoselectively into (Z)-3-chloroacrylonitriles by treatment with BCl₃ in the presence of stoichiometric amounts of imidazolium thiocyanates. These products could be readily functionalized to provide useful building blocks, thus demonstrating the synthetic value of the method. Preliminary mechanistic studies suggest initial activation of the cationic thiocyanate by the Lewis acid, followed by electrophilic attack of the alkyne. The syn addition of a chloride to the vinyl cation intermediate and final elimination of the thiourea unit afford the desired chloroacrylonitriles.