Radical amination with sulfonyl azides: a powerful method for the formation of C-N bonds

A novel reaction for the introduction of an azide moiety by means of a mild radical process is currently under development. Sulfonyl azides are suitable azidating agents for nucleophilic radicals, such as secondary and tertiary alkyl radicals. More electrophilic radicals, such as enolate radicals, do not react with sulfonyl azides. This feature allowed the development of efficient intra- and intermolecular carboazidations of olefins. Due to the versatility of the azido group, this reaction has an important synthetic potential, as already demonstrated by the preparation of the core of several alkaloids, particularly those containing an amino-substituted quaternary carbon center, such as FR901483.     

Synthesis and stereochemical studies of di and tetra 9,9′-spirobifluorene porphyrins: new building blocks for catalytic material

We report the synthesis and stereochemical properties of a new class of molecules containing a covalently-linked porphyrin and spiro-9,9′-bifluorene derivatives. The large spiro substituents hinder rotation about the meso position to give atropisomers which can be detected by ¹H NMR after phosphine or isocyanide complexation to the ruthenium spiroporphyrins.     

Factors affecting the reactivity of thiol-functionalized mesoporous silica adsorbents toward mercury(II)

Numerous mercaptopropyl-functionalized silica spheres have been prepared by either post-synthesis grafting of MCM-41 and MCM-48 or self-assembly co-condensation of mercaptopropyltrimethoxysilane (MPTMS) or mercaptopropyltriethoxysilane (MPTES) and tetraethoxysilane (TEOS) precursors in hydroalcoholic medium in the presence of a cationic surfactant as templating agent and ammonia as catalyst. These materials of approximately the same particle size and morphology featured different functionalization levels, various degrees of structural order, and variable distribution of thiol groups in the mesopores. Their reactivity in solution has been studied using Hg(II) as model analyte. Total accessibility (on a 1:1 S:Hg stoichiometry basis) was demonstrated and quantified for well-ordered materials whereas less open and less organized structures with high degrees of functionalization were subject to less-than-complete loadings. Capacities measured at pH 2 were lower than at pH 4 because of distinct mercury-binding mechanisms. Kinetics associated to the uptake process were studied by in situ electrochemical monitoring of Hg(II) consumption from aqueous suspensions containing the various adsorbents. They indicate only little difference between materials of the MCM-41 and MCM-48 series at similar functionalization levels, fast mass transport in well-ordered mesostructures in comparison to the poorly or non-ordered ones (except at pH 2 where charge formation induced some restriction in materials characterized by long-range structural order), and even faster processes in the wormlike frameworks (characterized by shorter range structural order). Hg(II) binding to thiol-functionalized materials obtained by post-synthesis grafting was found to occur more rapidly in the early beginning of the uptake process as a result of a higher concentration of binding sites at the pore entrance in comparison to the more homogeneous distribution of these groups in the mesochannels of materials obtained by co-condensation.     

Synthesis of 5-aryl-5′-formyl-2,2′-bithiophenes as new precursors for nonlinear optical (NLO) materials

A series of formyl-substituted 5-aryl-2,2′-bithiophenes 5 were synthesized using two different methods: Vilsmeier-Haack-Arnold reaction (VHA) or through Suzuki coupling. The synthesis of compounds 5 through the Vilsmeier-Haack-Arnold reaction, starting from inexpensive and easily available precursors such as acetophenones, gave the title compounds in low yields after four reaction steps. On the other hand Suzuki coupling of functionalized arylboronic acids 7 and the 5-bromo-5′-formyl-2,2′-bithiophene 6 gave compounds 5 in good yields in only one step.     

Synthesis and biological evaluation of potent glycosidase inhibitors: 4-deoxy-4,4-difluoroisofagomine and analogues

A series of 4,4-difluoroisofagomine analogues were synthesized. These compounds were tested for inhibition of eight glycosidases. The 3R,5R isomer 1 is a new and potent inhibitor against β-glucosidase from almonds with K_i value of 1.2 μM. The influence of the gem-difluoromethylene group (CF₂) on binding to glycosidases is discussed. It is concluded that only non-essential hydroxyl groups can be replaced by the gem-difluoro group and that in such a case (β-glycosidase) the change in inhibition is, interestingly, a result of the change in base strength.     

Tosylated glycerol carbonate, a versatile bis-electrophile to access new functionalized glycidol derivatives

The reactivity of tosylated glycerol carbonate 2 toward nucleophiles has been exploited to generate glycidol analogues protected with carbonate or carbamate groups. The activated glycerol 2 is a reasonable linking agent with thiol and alcohol nucleophiles and an excellent and selective one with primary amines, allowing efficient bis-functionalizations of glycerol.     

Modular access to heterocycles: methyl 3-aminobenzo[<Emphasis Type="Italic">b</Emphasis>]thiophene-2-carboxylate–thiourea linkage or pyrimidine-4-one-2-thione formation

Abstract  Modular conditions for the formation of thioureas or pyrimidine-4-one-2-thiones connected to the benzo[b]thiophene, benzene and indole structures were performed. A benzo[b]thiophene isothiocyanate derivative was used as a model to study the condensation with simple aromatic amines and amino-l-sorbose derivative. The construction of pyrimidine-4-one-2-thiones using basic conditions afforded efficiently new heterocyclic aromatics, which were further transformed using the alkylated sulfur as a leaving group in palladium-catalyzed cross-coupling reactions. Graphical abstract        

Oligothiophene Self‐Assembly on the Surface of ZnO Nanorods: Toward Coaxial p–n Hybrid Heterojunctions

We describe herein the design, synthesis and detailed structural characterization of hybrid 1D nanostructures. They are prepared by supramolecular self‐assembly of oligothiophene molecules on the surface of zinc oxide nanorods in solution at room temperature. Electronic absorption spectroscopy and X‐ray diffraction show that both organic and inorganic components in the coaxial p–n heterojunctions are crystalline. Especially, it is demonstrated that the organic compounds form a self‐assembled monolayer at the surface of the nanorods, which is not the case when zinc oxide quantum dots are instead used. As a result of their hybrid nature, the 1D nanostructures lead to ambipolar semiconducting nanostructured materials as active layers in field‐effect transistors.     

Intramolecular Homolytic Substitution of Sulfinates and Sulfinamides

A general and efficient method for the synthesis of cyclic sulfinates and sulfinamides based on intramolecular homolytic substitution (S_Hi) at the sulfur atom by aryl or alkyl radicals is described. Both alkyl and benzofused compounds can be accessed directly from easily prepared acyclic precursors. Enantiomerically enriched sulfur‐based heterocycles were formed through an S_Hi process with inversion of configuration at the sulfur atom. Cyclization of prochiral radicals proceeded with varying stereochemical outcomes, depending on the size of the incoming radical. 2‐Pyridyl and 2‐quinolyl radicals led to biaryl compounds, which result from attack onto the ortho position of the arylsulfinate rather than a thiophilic substitution.