AT-CuAAC Synthesis of Mechanically Interlocked Oligonucleotides.

We present a simple strategy for the synthesis of main chain oligonucleotide rotaxanes with precise control over the position of the macrocycle. The novel DNA-based rotaxanes were analyzed to assess the effect of the mechanical bond on their properties.

Stereoselective Synthesis of Mechanically Planar Chiral Rotaxanes.

Chiral interlocked molecules in which the mechanical bond provides the sole stereogenic unit are typically produced with no control over the mechanical stereochemistry. Here we report a stereoselective approach to mechanically planar chiral rotaxanes in up to 98:2 d.r. using a readily available α-amino acid-derived azide. Symmetrization of the covalent stereocenter yields a rotaxane in which the mechanical bond provides the only stereogenic element.

Properties and emerging applications of mechanically interlocked ligands.

Mechanically interlocked molecules have a long and rich history as ligands thanks to the key role coordination chemistry has played in the development of high yielding passive template syntheses of rotaxanes and catenanes. In this Feature Article, we highlight the effect of the mechanical bond on the properties of metal ions bound within the sterically hindered environment of the macrocycle cavity, and discuss the emerging applications of interlocked ligands in catalysis, sensing and supramolecular materials.

Scalable anti-Markovnikov hydrobromination of aliphatic and aromatic olefins.

To improve access to a key synthetic intermediate we targeted a direct hydrobromination-Negishi route. Unsurprisingly, the anti-Markovnikov addition of HBr to estragole in the presence of AIBN proved successful. However, even in the absence of an added initiator, anti-Markovnikov addition was observed. Re-examination of early reports revealed that selective Markovnikov addition, often simply termed "normal" addition, is not always observed with HBr unless air is excluded, leading to the rediscovery of a reproducible and scalable initiator-free protocol.

Engaging Copper(III) Corrole as an Electron Acceptor: Photoinduced Charge Separation in Zinc Porphyrin-Copper Corrole Donor-Acceptor Conjugates.

An electron-deficient copper(III) corrole was utilized for the construction of donor-acceptor conjugates with zinc(II) porphyrin (ZnP) as a singlet excited state electron donor, and the occurrence of photoinduced charge separation was demonstrated by using transient pump-probe spectroscopic techniques. In these conjugates, the number of copper corrole units was varied from 1 to 2 or 4 units while maintaining a single ZnP entity to observe the effect of corrole multiplicity in facilitating the charge-separation process. The conjugates and control compounds were electrochemically and spectroelectrochemically characterized. Computational studies revealed ground state geometries of the compounds and the electron-deficient nature of the copper(III) corrole. An energy level diagram was established to predict the photochemical events by using optical, emission, electrochemical, and computational data. The occurrence of charge separation from singlet excited zinc porphyrin and charge recombination to yield directly the ground state species were evident from the diagram. Femtosecond transient absorption spectroscopy studies provided spectral evidence of charge separation in the form of the zinc porphyrin radical cation and copper(II) corrole species as products. Rates of charge separation in the conjugates were found to be of the order of 10(10)  s(-1) and increased with increasing multiplicity of copper(III) corrole entities. The present study demonstrates the importance of copper(III) corrole as an electron acceptor in building model photosynthetic systems.

A Stimuli-Responsive Rotaxane-Gold Catalyst: Regulation of Activity and Diastereoselectivity.

A rotaxane-based Au catalyst was developed and the effect of the mechanical bond on its behavior was studied. Unlike the non-interlocked thread, the rotaxane requires a catalytically innocent cofactor, the identity of which significantly influences both the yield and diastereoselectivity of the reaction. Under optimized conditions, Au(I) (the catalyst), Ag(I) (to abstract the Cl(-) ligand), and Cu(I) (the cofactor) combine to produce a catalyst with excellent activity and selectivity.

Solvent switchable cycloaddition: a (one-pot) metal-free approach towards N-substituted benzo[e]- or [f]isoindolones via C(sp(2))-H functionalization.

The tuning of selective ring closure is a nontrivial challenge in synthetic organic chemistry. Herein we report a solvent switchable metal-free [4 + 2] cycloaddition approach via Csp(2)-H functionalization. The protocol is highly atom economical with water being the only by-product, delivering N-substituted benzo[e]- or [f]isoindolones in high yields.

Synthesis of (spiro)cyclopentapyridinones via C(sp3)-H functionalization: a post-Ugi gold-catalyzed regioselective tandem cyclization.

A gold-catalyzed regioselective tandem cyclization of N-propynylbutynamide via Csp(3)-H functionalization has been described, providing a distinctive methodology for the architecture of cyclopentapyridinones as well as spirocyclopentapyridinones.

Highly efficient intramolecular Cannizzaro reaction between 1,3-distal formyl groups at the upper rim of a cone-calix[4]arene.

The 1,3-distal cone-calix[4]arene dialdehyde 1 undergoes Cannizzaro disproportionation in the presence of strong base, but its 1,2-vicinal regioisomer 3 and the analogous monoaldehyde 2 are unreactive under the same conditions. The high intramolecular reactivity of the 1,3-distal regioisomer 1 is measured and discussed in terms of Effective Molarity (EM).