Acyliminium ions and related species are potent electrophiles that can be quite valuable in the synthesis of nitrogen-containing molecules. This manuscript describes a protocol to form these intermediates through hydride abstractions of easily accessible allylic carbamates, amides, and sulfonamides that avoids the reversibility that is possible in classical condensation-based routes. These intermediates are used in the preparation of a range of nitrogen-containing heterocycles, and in many cases high levels of sterocontrol are observed. Specifically areas of investigation include the impact of chemical structure on oxidation efficiency, the geometry of the intermediate iminium ions, the impact of a substrate stereocenter on stereocontrol, and an examination of transition state geometry.

Storing solar energy is a key challenge in modern science. MOlecular Solar Thermal (MOST) systems, in particular those based on azobenzene switches, have received great interest in the last decades. The energy storage properties of azobenzene (t1/2 < 4 days; DH~270 kJ/kg) must be improved for future applications. Herein, we introduce peptoids as programmable supramolecular scaffolds to improve the energy storage properties of azobenzene-based MOST systems. We demonstrate with 3-unit peptoids bearing a single azobenzene chromophore that dynamics of the MOST systems can be tuned depending on the anchoring position of the photochromic unit on the macromolecular backbone. We measured a remarkable increase of the half-life of the metastable form up to 14 days at 20 °C for a specific anchoring site, significantly higher than the isolated azobenzene moiety, thus opening new perspectives for MOST development. We also highlight that liquid chromatography coupled to mass spectrometry does not only enable to monitor the different stereoisomers during the photoisomerization process as traditionnaly done, but also allows to determine the thermal back-isomerization kinetics.

Carbon-centered radicals stabilized by adjacent boron atoms are underexplored reaction intermediates in organic synthesis. We report the development of vinyl cyclopropyl diborons (VCPDBs) as a versatile source of previously unknown homoallylic α,α-diboryl radicals via thiyl radical catalyzed diboron-directed ring opening. These diboryl stabilized radicals underwent smooth [3+2] cycloaddition with a variety of olefins to provide diboryl cyclopentanes in good to excellent diastereoselectivity. In contrast to the trans-diastereoselectivity observed with most of the dicarbonyl activated VCPs, the cycloaddition of VCPDBs showed a remarkable preference for formation of cis-cyclopentane diastereomer which was confirmed by quantitative NOE and 2D NOESY studies. The cis-stereochemistry of cyclopentane products enabled a concise intramolecular Heck reaction approach to rare tricyclic cyclopentanoid framework containing the diboron group. The mild reaction conditions also allowed a one-pot VCP ring-opening, cycloaddition-oxidation sequence to afford disubstituted cyclopentanones. Control experiments and DFT analysis of reaction mechanism support a radical mediated pathway and provide a rationale for the observed diastereoselectivity. To our knowledge, these are the first examples of the use of geminal diboryl group as an activator of VCP ring opening and cycloaddition reaction of α-boryl radicals.

The anion recognition and electrochemical anion sensing properties of halogen bonding (XB) tripodal zinc (II)-receptors strategically designed and constructed for tetrahedral anion guest binding are described. The XB tris(iodotriazole)-containing hosts exhibit high affinities and selectivities for inorganic phosphate over other more basic, mono-charged oxoanions such as acetate and the halides in a competitive CH3CN/ D2O 9:1 v/v aqueous solvent mixture. 1H NMR anion binding and electrochemical voltammetric anion sensing studies with redox-active ferrocene functionalised metallo-tripodal receptor analogues, reveal each of the XB tripods as superior anion complexants when compared to their tris(prototriazole)-containing, hydrogen bonding (HB) counterparts, not only exemplifying the halogen bond as a strong alternative interaction to the traditional hydrogen bond for molecular recognition but also providing rare evidence of the ability of XB receptors to preferentially bind the ‘harder’ phosphate oxoanion over the ‘softer’ and less hydrated halides in aqueous containing media.

While many dye binding aptamers have been reported, most of them were for light-up aptamers that can significantly enhance the quantum yield of fluorophores. Sulforhodamine B (SRhB) was used as a target previously to select both DNA and RNA aptamers, and the DNA aptamer was a G-quadruplex that can bind to a number of rhodamine analogs. In addition, the previous selections were performed by immobilizing the target molecules. In this work, we used the library immobilization method to respectively select aptamers for SRhB and fluorescein. The SRhB aptamer has a non-G-quadruplex structure with a Kd of 1.0 µM measured from isothermal titration calorimetry. Upon titration of the aptamer, the fluorescence of SRhB increased 2.5-fold, and this aptamer does not require Mg2+ for binding. Rhodamine B has even tighter binding suggesting binding through the xanthene moiety of the dyes. No binding was detected for fluorescein. For the fluorescein selection, a dominant aptamer sequence with a Kd of 147 µM was obtained. This study provides two new aptamers for two important fluorophores that can be used to study aptamer-based separation, dye detection and catalysis. Comparison of these aptamers also provide insights into the effect of functional groups on aptamer binding.

The synthesis and characterization of novel N-heterocyclic carbene (NHC) stabilized dialanes Al2Mes4 as well as first investigations concerning the reactivity of these compounds are reported. The synthesis of these compounds proceeds via the Mesityl-substituted alanes (NHC)·AlHMes2 (NHC = IMeMe3, IiPrMe4) and iodo-alanes (NHC)·AlIMes2 (NHC = IMeMe5, IiPrMe6). Metallic reduction of 5 and 6 afforded the new NHC-stabilized dialanes (NHC)2·Al2Mes4 (NHC = IMeMe7, IiPrMe8). The NHC-ligated dialanes are thermally robust and storable synthons for the dialane Al2Mes4. First reactivity studies on (IMeMe)2·Al2Mes47 towards small molecules confirm this, as 7 shows controlled and selective reactions with several substrates. Reaction with CuCl leads to oxidation of the dialane and formation of (IMeMe)·AlClMes210, reactions with pyridine N-oxide and tBu-N=C=S, respectively, gave the chalcogenide-bridged dimers ((IMeMe)·AlMes2)2-μ-E (E= O 11, S 12), and reaction with acetylene afforded the dimetallaacetylide ((IMeMe)·AlMes2)2-μ-(C≡C) 13.

Studies of the supramolecular chemistry of iso-tellurazole N-oxides have been confined to non-polar media until now. To overcome that limitation, an iso-tellurazole N-oxide was derivatized with a primary alcohol group; the compound is soluble in polar solvents and stable in acidic to neutral aqueous media. Nickel (II) and iron (II) form macrocyclic complexes with six molecules of that isotellurazole N-oxide in a hitherto not-observed macrocyclic arrangement defined by CTe…O chalcogen bonds and κ6-O bound to the metal ion. This behaviour is in sharp contrast with the κn-Te (n = 1,2,4) complexes formed by soft metal ions.

Transition-metal-catalyzed coupling reactions that involve the direct functionalization of insert C-H bond represent one of the most efficient strategies for forming carbon-carbon bonds. Herein, a palladium-catalyzed intramolecular C-H bond arylation of triaryl phosphates is reported to access seven-membered cyclic biarylphosphonate targets. The reaction is achieved via a unique eight-membered palladacyclic intermediate and shows good functional group compatibility. Meanwhile, the product can be readily converted into other valuable phosphate compounds.

Hybrid organic-inorganic molecules have recently received great interest due to their unique properties, which give access to their implementation in biological and material sciences. Herein, a new synthetic approach for the direct-linkage of the purely inorganic dodecaborate cluster to organic building blocks through B-C bond is established, using boronic acids as functional groups on the organic moiety, reacting under Suzuki-Miyaura coupling conditions with iodo-undecahydridododecaborate. The choices of ligand (DavePhos) and solvent (N-methylpyrrolidone for electron-poor, CD3CN for electron-rich groups) are essential for the successful coupling. Ultimately, the newly described methodology is found to be functional-group tolerant covering a wide spectrum of substrates including electron-poor arenes.

“We aimed to push the absolute configuration capacity of X-ray diffraction to its limit.” This and more about the story behind the front cover can be found in the article at 10.1002/chem.202302217).

Abstract

Invited for the cover of this issue is the group of Bo Wang at Biogen. The image depicts the sectored chiral domains of urea inclusion compounds. Read the full text of the article at 10.1002/chem.202302217.