Photocatalytic Difunctionalization of Vinyl Ureas by Radical Addition Polar Truce–Smiles Rearrangement Cascades

We report tandem alkyl‐arylations and phosphonyl‐arylations of vinyl ureas by way of a photocatalytic radical‐polar crossover mechanism. Addition of photoredox‐generated radicals to the alkene forms a new C?C or C?P bond and generates a product radical adjacent to the urea function. Reductive termination of the photocatalytic cycle generates an anion that undergoes a polar Truce–Smiles rearrangement, forming a C?C bond. The reaction is successful with a range of α‐fluorinated alkyl sodium sulfinate salts and diarylphosphine oxides as radical precursors, and the conformationally accelerated Truce–Smiles rearrangement is not restricted by the electronic nature of the migrating aromatic ring. Formally the reaction constitutes an α,β‐difuctionalisation of a carbon–carbon double bond, and proceeds under mild conditions with visible light and a readily available organic photocatalyst. The products are α,α‐diaryl alkylureas typically functionalized with F or P substituents that may be readily converted into α,α‐diaryl alkylamines.     

Chromatographic behavior of benzimidazole derivatives on hypercrosslinked polystyrene by reverse-phase HPLC

Abstract

An important part in the research of separation of various compound classes is the study of relationship between structure and property by describing the effect of structure on compounds’ chromatographic retention. The aim of this work was to study the chromatographic retention of the firstly synthesized benzimidazoles from water-acetonitrile and water-methanol solutions on hypercrosslinked polystyrene (HCP) by high-performance liquid chromatography (HPLC). The effect of water-methanol and water-acetonitrile solutions’ composition on the benzimidazole derivative retention factors on HCP was studied. The thermodynamic characteristics of sorption of benzimidazoles’ transition from water-organic solutions onto the surface of HCP phase were obtained. The thermodynamic compensation effects were studied. It has been shown that the benzimidazole nitro derivative realizes additional specific interactions with the aromatic network of HCP. The slope ratio of the Soczewiński–Wachtmeister equation was calculated. It was shown that 1-hydroxymethylbenzimidazole and 2-aminobenzimidazole characterized by small volumes and containing hydrophilic substituents do not subordinate Soczewiński–Wachtmeister model under ranging from 75 to 85% concentrations of acetonitrile.     

Electronic Structures and Chiroptical Properties of Post‐functionalized Helicene Quinones

The synthesis of redox‐active p‐ and o‐quinones 2‐phenylamino‐4‐phenylimino[6]helicene‐1‐one 1 , 2‐phenylamino[6]‐helicene‐1,4‐dione 2 , and 4‐phenyl[6]helicene‐1,2‐dione 3 in their enantiopure forms by post‐functionalization of (P)‐ and (M)‐1,2‐dimethoxy[6]helicene is presented. Structural characterization in solution and in the solid state was accomplished by 2D NMR spectroscopy methods and X‐ray diffraction analysis, respectively. Interpretation of electrochemical redox data was accompanied by a detailed orbital picture, derived from DFT calculations. The electronic structures of compounds 1 – 3 were investigated by UV/Vis and electronic circular dichroism (ECD) spectroscopy, complemented by TD‐DFT calculations. Quinones 1 – 3 were chemically reduced to study the EPR signatures of their respective radical anions. DFT methods were used for the atom assignment of the hyperfine coupling constants. The results are discussed within the context of electrochromic chiral switches and molecular recognition.     

Introducing a Hydrogen‐Bond Donor into a Weakly Nucleophilic Brønsted Base: Alkali Metal Hexamethyldisilazides (MHMDS,M=Li,Na, K,Rb and Cs) with Ammonia

Alkali metal 1,1,1,3,3,3‐hexamethyldisilazide (MHMDSs) are one of the most utilised weakly nucleophilic Brønsted bases in synthetic chemistry and especially in natural product synthesis. Like lithium organics, they aggregate depending on the employed donor solvents. Thus, they show different reactivity and selectivity as a function of their aggregation and solvation state. To date, monomeric LiHMDS with monodentate donor bases was only characterised in solution. Since the first preparation of LiHMDS in 1959 by Wannagat and Niederprüm, all efforts to crystallise monomeric LiHMDS in the absence of chelating ligands failed. Herein, we present ammonia adducts of LiHMDS, NaHMDS, KHMDS, RbHMDS and CsHMDS with unprecedented aggregation motifs: 1) The hitherto missing monomeric key compound in the LiHMDS aggregation architectures. Monomeric crystal structures of trisolvated LiHMDS ( 1 ) and NaHMDS ( 2 ), showing unique intermolecular hydrogen bonds, 2) the unprecedented tetrasolvated KHMDS ( 3 ) and RbHMDS ( 4 ) dimers and 3) the disolvated CsHMDS ( 5 ) dimer with very close intermolecular Si?CH₃???Cs s‐block “agostic” interactions have been prepared and characterised by single‐crystal X‐ray structure analysis.     

Stibinidene and Bismuthinidene as Two‐Electron Donors for Transition Metals (Co and Mn)

The reaction of stibinidene and bismuthinidene ArM [where Ar=C₆H₃‐2,6‐(CH=NtBu)₂; M=Sb ( 1 ), Bi ( 2 )] with transition metal (TM) carbonyls Co₂(CO)₈ and Mn₂(CO)₁₀ produced unprecedented ionic complexes [(ArM)₂Co(CO)₃]⁺[Co(CO)₄]^? and [(ArM)₂Mn(CO)₄]⁺[Mn(CO)₅]^? [where M=Sb ( 3 , 5 ), Bi ( 4 , 6 )]. The pnictinidenes 1 and 2 behaved as two‐electron donors in this set of compounds. Besides the M→TM bonds, the topological analysis also revealed a number of secondary interactions contributing to the stabilization of cationic parts of titled complexes.     

SnS and SnS2 thin films deposited using a spin‐coating technique from intramolecularly coordinated organotin sulfides

Synthesis and applications of organotin(II) sulfide ({2,6‐(Me₂NCH₂)₂C₆H₃}Sn)₂(μ‐S) ( 1 ), organotin(II) thiophenolate {2,6‐(Me₂NCH₂)₂C₆H₃}Sn(SPh) ( 2 ) and organotin(IV) heptasulfide {2,6‐(Me₂NCH₂)₂C₆H₃}₂Sn₂S₇ ( 3 ) as potential single‐source precursors (SSPs) for the deposition of SnS or SnS₂ thin films using a spin‐coating method are reported. Compounds 1 , 2 and 3 differ either by tin oxidation state or by Sn:S ratio (Sn:S = 2:1 in 1 , 1:1 in 2 and 2:7 in 3 ). It is shown that compound 1 is not a suitable SSP for thin‐film fabrication using the spin‐coating process because of its incomplete decomposition at annealing temperature. However, compounds 2 and 3 seem to be promising SSPs for spin‐coating of amorphous semiconducting thin films of SnS and SnS₂, respectively. Copyright © 2015 John Wiley & Sons, Ltd.