We report a new family of hexa‐peri‐hexabenzocoronene (HBC)‐based helical nanographenes incorporating π‐extended carbo[5]helicenes bearing an octagonal carbocycle. This family represents a new kind of highly distorted saddle‐helix hybrid nanographenes. For the first time, the eight‐membered ring becomes a constituent of both a carbo[5]helicene and a HBC and thus, the negative curvature is responsible for twisting both units. This novel chiral motif, namely, oct‐[5]helicene results in the largest torsion angle recorded so far for a carbo[5]helicene (θ=79.5°), as it has been suggested by DFT‐calculations and confirmed by X‐ray crystallography. Consequently, the barriers of isomerization become exceptionally high for a [5]helicene unsubstituted in the fjord region since neither racemization nor decomposition were observed at 200 °C for 1 or 3 during 5 h. Therefore, racemic resolutions allowed subsequent chiroptical studies showing the ECD and CPL responses of this novel family of chiral nanographenes.

Abstract:Simple Brønsted acids such as p-toluenesulfonic acid monohydrate (PTS) or polymer-bound p-toluenesulfonic acid efficiently catalyze the direct nucleophilic substitution of the hydroxy group of allylic and benzylic alcohols with a large variety of carbon-and heteroatom-centered nucleophiles. Reaction conditions are mild, the process is conducted under an atmosphere of air without the need for dried solvents, and water is the only side product of the reaction.Keywords: alcohols; C À C coupling; nucleophilic substitution; supported catalysts; synthetic methodsThe construction of C À C bonds is a fundamental reaction in organic synthesis and coupling reactions between reactive nucleophiles (NuH) and halides (RX) or related species are one of the most used strategies. In this context, direct substitution of the hydroxy group in alcohols by nucleophiles could be considered as an ideal process because of the wide availability of the starting materials and the generation of H 2 O as the only side product. However, the main limitation of this strategy is that an excess of sulfuric acid, polyphosphoric acid, [1] or a stoichiometric amount of a Lewis acid [2] is required, and so the range of possible nucleophiles is limited. Therefore, the development of catalytic versions of this reaction remains as a major objective of the modern organic chemistry (Scheme 1). Recent advances in this field are based on the use of transition metal complexes as catalysts. Remarkable are the Ru-, [3] Re-, [4] and Au-catalyzed [5] propargylation of nucleophiles with propargylic alcohols, the Tsuji-Trost reaction of allylic alcohols with active methylene compounds, [6] the reaction of secondary benzylic alcohols with different nucleophiles catalyzed by La, Sc, or Hf salts, [7] and the Fe-, or Au-catalyzed arylation of benzylic alcohols.[8] In addition, InCl 3 has emerged as a powerful catalyst to perform direct nucleophilic substitution of allylic and benzylic alcohols. [9] Although the catalytic activation of alcohols is thought to be difficult due to the poor leaving ability of the OH group, we have recently found that simple Brønsted acids like p-toluenesulfonic acid monohydrate (PTS) catalyze the direct nucleophilic substitution of propargylic alcohols.[10] Herein we report a strategy involving simple Brønsted acid-catalyzed activation of allylic and benzylic alcohols as a method for the direct formation of new C À C and C À heteroatom bonds from carbon (active methylene compounds, aromatic and heteroaromatic compounds), nitrogen, sulfur, and oxygen nucleophiles and alcohols. Surprisingly, the Brønsted acid-catalyzed direct substitution of allylic alcohols has not been reported in the literature and so no systematic study has so far been performed. Moreover, in some recent papers this reaction has been reported not to proceed at all. [9b] Despite all these negative forewarnings, we decided to investigate the reaction of allylic alcohol 1a as a model substrate with selected nucleophiles 2-8 under PTS-catalyzed conditions (Sche...

In this paper, we have systematically studied how the replacement of a benzene ring by a heterocyclic compound in oligo(phenyleneethynylene) (OPE) derivatives affects the conductance of a molecular wire using the scanning tunneling microscope-based break junction technique. We describe for the first time how OPE derivatives with a central pyrimidine ring can efficiently link to the gold electrode by two pathways presenting two different conductance G values. We have demonstrated that this effect is associated with the presence of two efficient conductive pathways of different length: the conventional end-to-end configuration, and another with one of the electrodes linked directly to the central ring. This represents one of the few examples in which two defined conductive states can be set up in a single molecule without the aid of an external stimulus. Moreover, we have observed that the conductance through the full length of the heterocycle-based OPEs is basically unaffected by the presence of the heterocycle. All these results and the simplicity of the proposed molecules push forward the development of compounds with multiple conductance pathways, which would be a breakthrough in the field of molecular electronics.

Novel iron nanoparticles-based supramolecular hydrogels are described. These materials present enhanced mechanical strength keeping a water-like diffusion behaviour.

This tutorial review highlights the development of radical-based bioinspired synthesis of terpenes from the initial proposal to the development of modern catalytic methods for performing such processes. The power of the radical approach is demonstrated by the straightforward syntheses of many natural products from readily available starting materials. The efficiency of these processes nicely complements the described cationic polyolefin cyclisations and even suggests that modern radical methods provide means to improve upon nature's synthetic pathways.