Lawesson's reagent is one of the most common thionating reagents that has found use for several decades on a variety of carbonyl systems. Herein, we report the transformation of the 2‐λ5‐phosphaquinolin‐2‐one structure to its respective 2‐λ5‐phosphaquinolin‐2‐thione derivative. Solution‐state characterization of both P−OPh and P−Ph thio analogues, as well as solid‐state structures for the latter system, are reported.
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Abstract We examine the effects of fusing two benzofurans to
s ‐indacene (indacenodibenzofurans, IDBFs) and dicyclopenta[b,g ]naphthalene (indenoindenodibenzofurans, IIDBFs) to control the strong antiaromaticity and diradical character of these core units. Synthesis via 3‐functionalized benzofuran yieldssyn ‐IDBF andsyn ‐IIDBF.syn ‐IDBF possesses a high degree of paratropicity, exceeding that of the parent hydrocarbon, which in turn results in strong diradical character forsyn ‐IIDBF. In the case of theanti ‐isomers, synthesized via 2‐substituted benzofurans, these effects are decreased; however, both derivatives undergo an unexpected ring‐opening reaction during the final dearomatization step. All the results are compared to the benzothiophene‐fused analogues and show that the increased electronegativity of oxygen in thesyn ‐fused derivatives leads to enhancement of the antiaromatic core causing greater paratropicity. Forsyn ‐IIDBF increased diradical character results from rearomati‐zation of the core naphthalene unit in order to relieve this paratropicity. -
Abstract Cyclophanes are a venerable class of macrocyclic and cage compounds that often contain unusual conformations, high strain, and unusual properties. However, synthesis of complex, functional derivatives remains difficult due to low functional group tolerance, high dilution, extreme reaction conditions, and sometimes low yields using traditional stepwise synthetic methods. “Design of experiments” (DOE) is a method employed for the optimization of reaction conditions, and we showcase this approach to generate a dramatic increase in the yield of specific targets from two different self‐assembling systems. These examples demonstrate that DOE provides an additional tool in tuning self‐assembling, dynamic covalent systems.
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Abstract We describe two novel hybrid receptors combining a phosphorus‐/nitrogen‐containing (PN) phosphonamidate heterocycle with urea recognition units in an arylethynyl backbone. Structural, spectroscopic and computational studies reveal that the origin of superior binding for hydrogen sulfate (HSO4−) anion is correlated with the formation of strong hetero‐complementary hydrogen bonds with the phosphonamidate motif. We further demonstrate that the hybrid host system is capable of capturing/transporting the HSO4−anion from an aqueous, biphasic system.
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Abstract A new class of macrocyclic angle‐strained alkynes whose size and reactivity can be precisely tuned by modular organic synthesis is disclosed. Detailed analysis of the size‐dependent structural and electronic properties provides evidence for considerable distortion of the alkyne units incorporated into the cycloparaphenylene (CPP)‐derived macrocycles. The remarkable increase of the alkyne reactivity with decreasing macrocycle size in [2+2]cycloaddition–retrocyclization was investigated by joint experimental and theoretical studies and the thermodynamic and kinetic parameters that govern this reaction were unraveled. Additionally, even the largest, least strained macrocycle in this series was found to undergo strain‐promoted azide–alkyne cycloaddition (SPAAC) efficiently under mild conditions, thereby paving the way to the application of alkyne‐containing CPPs as fluorescent “clickable” macrocyclic architectures.
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Abstract Hydrogen sulfide (H2S) is a biologically active molecule that exhibits protective effects in a variety of physiological and pathological processes. Although several H2S‐related biological effects have been discovered by using H2S donors, knowing how much H2S has been released from donors under different conditions remains challenging. Now, a series of γ‐ketothiocarbamate (γ‐KetoTCM) compounds that provide the first examples of colorimetric H2S donors and enable direct quantification of H2S release, were reported. These compounds are activated through a pH‐dependent deprotonation/β‐elimination sequence to release carbonyl sulfide (COS), which is quickly converted into H2S by carbonic anhydrase. The
p ‐nitroaniline released upon donor activation provides an optical readout that correlates directly to COS/H2S release, thus enabling colorimetric measurement of H2S donation. -
Abstract A set of fully‐conjugated indenofluorenes has been synthesized and confirmed by solid‐state structure analysis. The indeno[2,1‐
c ]fluorenes and their benzo‐fused analogues all contain the antiaromaticas ‐indacene core. The molecules possess high electron affinities and show a broad absorption that reaches into the near‐IR region of the electromagnetic spectrum. All of the featured compounds reversibly accept up to two electrons as revealed by cyclic voltammetry. Analysis of molecule tropicity using NICS‐XY scan calculations shows that, while theas ‐indacene core is less paratropic thans ‐indacene, benz[a]‐annulation further reduces the antiaromaticity of the core. Antiaromatic strength of theas ‐indacene core can also be tuned by the position of fusion of additional arenes on the outer rings. -
Abstract Cyclophanes are an admirable class of macrocyclic and cage compounds that often display unusual properties due to their high strain and unusual conformations. However, the exploration of new, complex cyclophanes has been encumbered by syntheses that can be low yielding, require harsh reaction conditions, and arduous purification steps. Herein, we discuss our work using metalloid-directed self-assembly and dynamic covalent chemistry to form cryptands. These were then subjected to mild conditions to produce discrete disulfide, thioether and hydrocarbon macrocycles in high yields. ‘Design of Experiments’ was then used to selectively synthesize targeted macrocycles from complex mixtures. 1 Introduction 2 Cryptands to Cyclophanes 3 Functionalizable Macrocycles 4 ‘Design of Experiments’ Targeted Synthesis 5 Conclusions and Outlookmore » « less