Structural Reevaluation of the Electrophilic Hypervalent Iodine Reagent for Trifluoromethylthiolation Supported by the Crystalline Sponge Method for X-ray Analysis

Design and Use of Electrophilic Thiocyanating and Selenocyanating Reagents: An Interesting Trend for the Construction of SCN- and SeCN-Containing Compounds

Organothiocyanate and organoselenocyanate compounds are of paramount importance in organic chemistry as they are key intermediates to access sulfur- and selenium-containing compounds. Therefore, among the different synthetic pathways to get SCN- and SeCN-containing molecules, original methodologies using electrophilic reagents have recently been explored. This Minireview will showcase the recent advances that have been made. In particular, the design of several electrophilic sources and their applications for the thiocyanation and the selenocyanation of various classes of compounds will be highlighted and discussed.

Synthesis and Reactivity of α-Cumyl Bromodifluoromethanesulfenate: Application to the Radiosynthesis of [18 F]ArylSCF3

A highly reactive electrophilic bromodifluoromethylthiolating reagent, α-cumyl bromodifluoro-methanesulfenate 1, was prepared to allow for direct bromodifluoromethylthiolation of aryl boron reagents. This coupling reaction takes place under copper catalysis, and affords a large range of bromodifluoromethylthiolated arenes. These compounds are amenable to various transformations including halogen exchange with [18 F]KF/K222  , a process giving access to [18 F]arylSCF3 in two steps from the corresponding aryl boronic pinacol esters.

Crystallography of encapsulated molecules

The crystallography of supramolecular host-guest complexes is reviewed and discussed as a part of small molecule crystallography. In these complexes, the host binds the guests through weak supramolecular interactions, such as hydrogen and halogen bonding, cation-π, anion-π, C-H-π, π-π, C-H-anion interactions and the hydrophobic effect. As the guest often shows severe disorder, large thermal motion and low occupancies, the reliable crystallographic determination of the guest can be very demanding. The analysis of host-guest interactions using tools such as Hirshfeld and cavity volume surface analysis will help to look closely at the most important host-guest interactions. The jewel in the crown of utilizing host-guest interactions in the solid-state is the recently developed Crystalline Sponge Method (CSM) by Makoto Fujita. This method, when successful, gives an accurate and unambiguous 3-D structure of the structurally unknown guest molecule from only micro- or nanogram amounts of the guest molecule. In the case of an optically pure enantiomer, its absolute configuration can be determined.

Direct Monofluoromethylthiolation with S-(Fluoromethyl) Benzenesulfonothioate

An electrophilic shelf-stable monofluoromethylthiolating reagent S-(fluoromethyl) benezenesulfonothioate (1) was developed. In the presence of a copper catalyst, reagent 1 coupled with a variety of aryl boronic acids to give the corresponding monofluoromethylthiolated arenes in high yields. In addition, addition of reagent 1 to alkyl alkenes in the presence of a silver catalyst gave alkyl monofluoromethylthioethers in high yields.

An Iodine-Vapor-Induced Cyclization in a Crystalline Molecular Flask

A vapor-induced cyclization has been observed in the host environment of a crystalline molecular flask (CMF), within which 1,8-bis(2-phenylethynyl)naphthalene (bpen), a diarenynyl system primed for cyclization, was exposed to iodine vapor to yield the corresponding indeno[2,1-α]phenalene species. The cyclization process, unique in its vapor-induced, solvent-free nature, was followed spectroscopically, and found to occur concurrently with the displacement of lattice solvent for molecular iodine in CMF⋅0.75 bpen⋅2.25 CHCl3 ⋅H2 O. The cyclization occurred under mild conditions and without the need to suspend the crystals in solvent. The ability of CMFs to host purely gas-induced reactions is further highlighted by the subsequent sequential oxidation reaction of cyclized 7-iodo-12-phenylindeno[2,1-α]phenalene (ipp) with molecular oxygen derived from air, yielding 12-hydroxy-7-iodo-2-phenylindeno[2,1-α]phenalen-1(12H)-one (hipp).

In Situ Observation of Thiol Michael Addition to a Reversible Covalent Drug in a Crystalline Sponge

A reversible Michael addition reaction between thiol nucleophiles and cyanoenones has been previously postulated to be the mechanism-of-action of a new family of reversible covalent drugs. However, the hypothetical Michael adducts in this mechanism have only been detected by spectroscopic methods in solution. Herein, the crystallographic observation of reversible Michael addition with a potent cyanoenone drug candidate by means of the crystalline-sponge method is reported. After inclusion of the cyanoenone substrate, the sponge crystal was treated with a thiol solution. Subsequent crystallographic analysis confirmed the single-crystal-to-single-crystal transformation of the substrate into the impermanent Michael adduct.

Structure determination of microbial metabolites by the crystalline sponge method

The structures of metabolites produced in microgram quantities by enzymatic reductions with baker's yeast were analyzed using the crystalline sponge method. The X-ray data provided reliable structures for trace metabolites including their relative and absolute stereochemistries that are not fully addressed by conventional NMR and LC-MS analyses. Technically, combining two or more chromatographic purification techniques is essential because, unlike abundant synthetic compounds, extracted metabolites contain many low level UV-silent impurities. The crystalline sponge method coupled with HPLC purification (LC-SCD) would thus be a useful method for metabolic analysis and drug discovery.

Visible Light-Promoted Decarboxylative Di- and Trifluoromethylthiolation of Alkyl Carboxylic Acids

Described herein is a new and straightforward decarboxylative di- and trifluoromethylthiolation of alkyl carboxylic acids promoted by visible light. This approach enables the synthesis of biologically relevant alkyl SCF2H and SCF3 compounds from cheap and abundant carboxylic acids. The method is operationally simple, using irradiation from household light sources, and its mild reaction conditions make it tolerant of a range of functional groups. The strategy employs electrophilic phthalimide-derived di- and trifluoromethylthiolation reagents and exploits the ability of the imidyl radical to carry a radical chain.

A saccharide-based crystalline sponge for hydrophilic guests

A mannose-based crystalline sponge was designed and synthesized for the crystalline sponge analysis of rather hydrophilic guests.

Recent progress in direct introduction of fluorinated groups on alkenes and alkynes by means of C-H bond functionalization

The direct introduction of fluorine and fluorinated building blocks has recently attracted a lot of attention and particularly the direct functionalization of alkenes and alkynes. This review will highlight the major progress recently made in that field, with a focus on photocatalyzed transformations, base-promoted processes, and transition metal-catalyzed functionalization of alkenes and alkynes. Special attention will be paid to explanations of the reaction mechanisms.

Capturing snapshots of post-synthetic metallation chemistry in metal-organic frameworks

Post-synthetic metallation is employed strategically to imbue metal-organic frameworks (MOFs) with enhanced performance characteristics. However, obtaining precise structural information for metal-centred reactions that take place within the pores of these materials has remained an elusive goal, because of issues with high symmetry in certain MOFs, lower initial crystallinity for some chemically robust MOFs, and the reduction in crystallinity that can result from carrying out post-synthetic reactions on parent crystals. Here, we report a new three-dimensional MOF possessing pore cavities that are lined with vacant di-pyrazole groups poised for post-synthetic metallation. These metallations occur quantitatively without appreciable loss of crystallinity, thereby enabling examination of the products by single-crystal X-ray diffraction. To illustrate the potential of this platform to garner fundamental insight into metal-catalysed reactions in porous solids we use single-crystal X-ray diffraction studies to structurally elucidate the reaction products of consecutive oxidative addition and methyl migration steps that occur within the pores of the Rh-metallated MOF, 1·[Rh(CO)2][Rh(CO)2Cl2].